Episode 177: biological controls part two

Yellow sticky traps can help to catch adult fungus gnats while nematodes deal with the larvae. Photograph: Andermatt UK.

Transcript

Episode 177

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Jane: Hello and welcome to On The Ledge podcast, bringing you planty information and fun since February 2017. I'm your host, Jane Perrone, and in this week's show it's part two of our pest control special. I'm talking about biological controls with Tessa Cobley and Andy Brown, plus I answer a question about Oxalis bulbs and we hear from listener, Tate.

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Jane: Thanks to my new Patreons this week: Amanda became a Crazy Plant Person, Esther and Tari became Ledge-ends and Simon became a SuperFan, while Jane left a payment on ko-fi.com. So whether you want to just make a one-off act of kindness by supporting the show, you can do that via ko-fi or straight through PayPal or if you want to become a Patreon and make a monthly contribution and unlock extra benefits like twice monthly episodes of An Extra Leaf, my bonus podcast, it's up to you. All the details are in the show notes at janeperrone.com

A special request now. I am finally putting together my episode on The Houseplant Expert, the book that has inspired me and many other people to get into houseplants from a young age, and I would love to have your input. So, if you've got a copy of The Houseplant Expert, if you perhaps bought one on my recommendation or you've had one for years, I would love you to record a quick voice memo on your phone, telling me what the book means to you and what you love about it. It can be as little as ten seconds long! It'll be great to have your voices in the show, so just record a voice memo on your phone, send that in to ontheledgepodcast@gmail.com and you might be hearing yourself in the show. Remember to include your name and where you are in the world. Don't be shy! Remember we had Susie, who is only seven, taking part in Meet the Listener, so you can do it! I believe in you!

ScottishPlantDad on Instagram got in touch with a great recommendation for listener Rachel, who was looking for some plant that would grow in a window above a panel heater, and we were discussing ways that you can keep your plants elevated away from the heater while still in the window. ScottishPlantDad's idea is brilliant! It is a radiator washing dry rail. If you don't know exactly what I mean, it's a piece of metal with white plastic coating on it, like you get dryers made out of, but this one has hooks on it that hook onto the window ledge, or indeed onto the window itself, and allow the plants to sit there and then you can hang things off it. If you're really struggling to envisage my poor description of this item I will put a link in the show notes so you can see exactly what I'm talking about.

ScottishPlantDad has also hung them from the window blinds, so there's different options. That's a great addition to our chat about window aesthetics and what you can put there in order to cram in more plants, so thank you ScottishPlantDad!

It's also time for an On The Ledge sowalong update! I haven't had a chance to sow anything more yet and, to be totally honest, if you have not sown a thing yet, do not panic! You have plenty of time! So that's a little message if you are starting to worry that you haven't got your seeds in yet, there is loads of time, so do not be disturbed about that. I've got lots more things I'm going to be sowing in the next few weeks, when I get a chance, which will probably be, I hope, over the Easter holidays, when I've stopped painting everything in sight. I've been painting my fence, my shed, my front room, random pieces of shelving! It's all been happening with the paintbrush here and I've probably still got some paint in my hair right now but, hopefully, once that's all over, I can get on with some sowing, which is far more fun.

What have you been up to? Well, Joan in Geneva, in Switzerland, has posted on Instagram showing off some Morning Glories, lovely flowers, very beautiful, trumpet-shaped blooms which can grow outside and some people do grow them inside as well, so well done Joan. SpicyTerracotta in Pennsylvania has been sowing seeds with third graders, well done SpicyTerracotta, and lots of things have been popping up, including Monstera deliciosa and Marigold. Bot9Girl in Maryland in the US has been sowing Gesneriad Society seeds. That's very exciting! I hope you know, if you're a regular listener, that if you join the Genseriad Society you can be part of their seed scheme and get some excellent seeds to try. Jonathan in Pennsylvania has been sowing Coleus and basil and more. Yes, I need to sow my Coleus. That's my top sowing item at the moment. ProperPropagule, what a great name, has baby Sinningia leucotricha seedlings. Awesome! BareTomatoes on Instagram has an impressive array of seedlings. I'm feeling slightly intimidated, BareTomatoes, and over on Facebook in the Houseplant Fans of On The Ledge group, John has been posting about a Joshua Tree, that's Yucca brevifolia. The seeds are all germinated and getting settled into soil. John's been wondering about the questing radicals that bend down to find the soil and make a hairpin turn in the first root, "Apparently, it's typical of the species but it sure looks weird," John writes. Anyone got any insight into that? I'd love to know and so would John.

Lindsay has cactus and succulent seeds for the sowalong. Well done for getting hold of those, Lindsay. I put a link in your post to a great leaflet from the British Cactus and Succulent Society on how to sow cactus and succulent seeds which I'll link in the show notes as well. Alina is looking for tips on chilli seed sowing. Do go back and listen to the chilli episode, Alina, and what I would say about chillies is they need loads of light and lots of warmth, so if you can put them on a heat mat - Public service announcement, always use a thermostat with a heat mat otherwise they can be dangerous - or a special propagator, then you will give them that heat they need. Once they're germinated, you can turn it off. It's just for the germination process but make sure they're in a nice sheltered spot and that you don't let them dry out and, hopefully, you'll have some success.

Emma has been posting on Facebook and her daughter has been getting in on the seed sowing and sowing Mimosa pudica. What a cool plant that is! I must do an episode on that sometime because it's so popular! So many people grow it for the sowalong and it's really cool. So maybe I'll add that to my list of episode ideas, which is admittedly huge, but I do love all your recommendations for episodes, so if you do want to hear me talk about something, then do let me know. I am in search of a Sinningia expert because somebody has requested an episode on those and, as a Gesneriadfan, I'm not going to say no to that! So if you know any Sinningia experts, put them in touch!

So, it's not too late to get involved in the sowalong. If you haven't listened to those sowalong episodes, I will put a link in the show notes so you can listen to them all and catch up. Keep on sowing people! It's great fun. It doesn't always work - my Clivia seeds have not germinated, boo! - but I've had lots of success. I've also not had my Agave seedlings germinate either, but I have had success with my Selenicereus and my Astrophytum and the wonderful Hoya serpensseeds that I've got, so, you win some, you lose some. That's life, isn't it?

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Jane: If you haven't listened to episode 176, the episode preceding this one, then stop! Go and have a listen to that first because in this episode I'm running the second part of my interview on biological controls with Tessa Cobley, of Ladybird Plantcare, and Andy Brown, of Andermatt UK. In this second part of the interview we get into the matter of treatments for thrips, mealybugs and scale, why Bti counts as a biological control and what the colours of different sticky traps mean.

Jane: Let's just talk a little bit about mealybugs. When I did a mealybug episode, there seemed to be some doubt over whether there was an effective biological control for mealybugs. Is that still the case or is there anything on the horizon that can tackle this very annoying pest of our cacti and succulents?

Tessa: The Brown Australian Ladybirds are the predator that I sell for mealybug, but I do put a lot of caveats and talk to people carefully about how they're growing, the conditions that they're growing in, where the plants are, because being a crawling, then flying, creature, you're going to have to try and keep them on the plant and giving them enough light and warmth to do their job. I think, as your expert said on that episode, they need a lot of mealybug to encourage them to stick around, which is why they don't work as well as other biologicals for other pests. I think it's best to put it that way, really.

Jane: This is the thing, if you've got a big greenhouse full of cacti and succulents, it might be effective, but possibly not if you've just got a couple of mealybugs on a succulent on the windowsill.

Tessa: If anyone wants to look it up, the University of Exeter had a problem with mealybugs in their beautiful glass atrium and they got some trees with mealybug. They introduced the Brown Australian Ladybirds and they covered the trees in horticultural fleece, so the trees look like these big clouds while the ladybirds are doing their job and that's to keep that biological control in place.

Jane: I see. Well, I went to Exeter and I don't remember trees in an atrium! I think they must have fancied it up since I was there. Wow!

Tessa: It's a bit fancier now, yes! Have a look on their Instagram - it's really interesting. They only did one post on it but there's a bit of commentary underneath and I think there's a place where you can have a look for more information. I've seen it in other countries, trees covered in fleece or mesh to keep biologicals in place but that's the first time I'd really seen it being used properly in the UK.

Jane: With these ladybirds, obviously they're not UK natives. Is there a concern about them escaping into the environment, or would they just not survive outside because it's not Australia?

Tessa: As Andy said, everything that's being used in the UK is perfectly safe and it does pose no threat to the indigenous populations.

Jane: Well, that's good to hear. One of the other things that I'm confused about is Bti-based products, like Mosquito Dunks and bits. Is that classed as a biological control to start with and do they actually work against fungus gnats? I would really love to know the answer to that, as somebody who's spent a lot of money on a tub of these things and hasn't had much success with them, so far. Do they count as a biological control?

Andy: They do. There are four categories of biological control. There's semiochemicals, they're chemicals that are typically released by insects for communicating with each other. There are microbials, so things like bacteria and fungi, and Bti Bacillus thuringiensis israelensis is a microbial, or classified as a microbial. Then we have macrobiologicals, things you tend to be able to see, the insects, the mites, the nematodes that we've been talking about mostly. Then there are natural substances, so they would be things like your plant extracts. So, yes, Bti is a biological control.

Jane: How come it's widely available in the US but really hard to get hold of in the UK? Is it just not licensed here for use by home growers?

Andy: Correct. The products available vary from country to country and part of that is the registration requirements in different countries and Bti is not approved for use in the UK.

Jane: Is that because it's not safe or just because it hasn't gone through the hurdles for being approved?

Andy: It hasn't gone through the hurdles of being approved for the home and garden market, Bt is an incredibly safe product with a very long history of use. And Bti for controlling fly larvae, Dipteras or Btks you can use against Lepidoptera (caterpillars) and there are a couple of other Bts in other parts of the world, as well.

Jane: Do you have to soak it in water and then apply the water onto the plants? Is that the best method?

Andy: It doesn't need soaking before use but, yes, you're looking to put it into the compost, then you're looking for the fly larvae to consume it and what Bt has in it, it has a toxin that breaks down the gut of the insect. So you're looking to put it into the soil and then for the fly larvae to consume it.

Jane: Okay, so I need to mix it in when I'm repotting?

Andy: Yes, or spraying it onto the top of the soil should work and depending on how moist your soil is, the fly larvae tend to live near the top of the soil surface. So, as long as you get into contact with the flies, either by spraying the surface or by incorporating it as you are potting.

Jane: Right, okay, that makes sense. Well I'll give it another go. I've got a big tub of the stuff. It's interesting that I did manage to get hold of some when it's not licensed in the UK. I can't quite remember where I got it from but I guess that's the wild west of the internet for you. I guess the same applies to here in the UK where Neem Oil is not licensed for pesticide use but people manage to get hold of it and use it anyway, so I guess it's the same thing in terms of the differences between different markets and different regulatory systems? One of the other things that people wanted to know was whether you could combine a biological control such as, say, something you're treating for spider mites with a spray, like a soap spray that you might be using, or something like SB Plant Invigorator. Can you combine the two, or is that spray going to also kill your biological control?

Tessa: I tend to tell people to use the spray up until they receive their biological control. Partly because using the spray before they arrive is a really good idea to reduce pest numbers, so that when the biologicals arrive they don't have such a big task, but also because it's a bit of a wide question and it's not one-fits-all. Something like Phytoseilius for spider mite, you can use that with the SB. They're so fast moving, they're not going to be too affected by the SB Plant Invigorator. It's a contact insecticide, so it doesn't leave a residue that's going to last and get rid of any insects. You're killing them on contact, so the Phytoseilius doesn't bother them. They're so fast they just keep moving. Because you don't want to add too much confusion when people are using biologicals, and potentially using biologicals for the first time, I tend to say to people to stop using their home-made, shop-bought, non-chemical insecticide the night before their biologicals are due to arrive just to avoid any confusion and to make sure that you're not getting rid of any of your biologicals that you've ordered, you're not reducing those in numbers as you're reducing the pests in numbers.

Jane: Sure, that makes total sense. One of the other pests that people seem to have real problems with, I have to say I'm touching wood now, I have never suffered from this particular pest, but thrips seem to be a real issue for many people. Sara got in touch because she was confused about the different types of predatory mites that you can get for thrips and has been told there's a preventative one and one to use when there's presence. Can you go through that, to just explain the differences for thrip treatments cucumeris and swirskii. Is that right?

Tessa: Yes, cucumeris is the slow-release product that I mentioned. It's predominantly sold in sachets with the breeding colony that crawl out over four to six weeks and eat the larval stage of the thrips. The other product that she mentions isn't licensed for home growers in the UK. It requires slightly warmer temperatures as well, so it's not something that is sold in the houseplant arena in this country anyway. The other products, you can use nematodes as well, and if you've really got a big thrip problem there's a brilliant bug called Aureus and they are super-fast and they eat all stages of the thrips, so they're obviously much more effective because they're not just killing and eating the smaller thrips and the young thrips, they're eating the adults as well. So, if you've got a big thrip problem and you want to get it sorted once and for all, well, not necessarily for all, but want to get it properly sorted, then you'd go with the Aureus.

Jane: One other question on a different pest that we haven't mentioned yet: are there any biological controls for scale?

Tessa: Yes. Again, you can use nematodes for scale, as a foliar spray. It requires a little bit more attention to detail because you may need to use a product to break the surface tension on the leaf, just like a soft soap or something like that, and then you spray the nematodes solution onto the plant and you then need to mist the plant a few times afterwards to keep that level of moisture onto the foliage. Obviously, we've talked about the fact that nematodes are a swimming creature and that's part of the reason they work really well for scale because they can actually get underneath the scale, which nothing else can.

Jane: I get a strange satisfaction from scraping away at scale! I don't know...

Tessa: Yes, I saw someone using masking tape to, like, wax their plants.

Jane: Yes, there's all kinds of ways of dealing with it. I say that, then I did have it on one plant which had particularly corrugated leaves and that was a nightmare because that's where I could have really done with the biological control because it was just so difficult to get them off the leaves, especially the young ones without damaging the leaves. Yes, I can imagine that would work extremely well. Andy, are there any things on the horizon in the world of biological controls?

Andy: Very much so. For me it's a really exciting industry to be part of because it is moving so quickly. The biocontrol industry is growing at a rapid rate globally and the UK is the same as that. There are a range of new predators and parasitoids coming through. Where they tend to start, is they tend to start in commercial horticulture, high-value crops and protected crops and, similar to the fleecing around the trees in Exeter, keeping them where you want them to be is a challenge and so the technologies tend to start in greenhouses. Then they evolve and come to the home and garden market.

Jane: So what do we need to do to help domestic growers really get to grips with biological controls? What's the best thing people can do if they want to get into biological controls but they don't really know where to start? Is it just a question of doing your research first and figuring out what pest you've got. I always recommend that people get themselves a hand lens so they can really see their pests up close, Is that the best place to start?

Tessa: Yes, I think that's really important, when I speak to customers, is them really, really knowing what pest they have. If they're really not sure, they can send photographs, descriptions of the damage, pictures of the damage and get help with identifying what pests they've got in the first place because you can't really go anywhere without knowing what problem you're dealing with.

Andy: There's a mountain of information out there available online, either searching through Google or going onto YouTube. There are loads of people who post videos on common problems they have and what they've done about it. For us, as suppliers, it's important for us to educate and work with our customers and, as I said, the people who work in this industry are very passionate about it and we're always happy to talk to people about what it is they have and what they need to do.

Jane: I just worry sometimes about the poor advice that's out there on the internet, not specifically about biological controls, but about how to deal with pests. There's some weird concoctions that people are mixing up. That worries me.

Tessa: Yes, you mentioned Neem Oil and I worry that people are just liberally spraying Neem Oil on everything and hoping for the best and also then using Neem Oil, once their biologicals were in place, and potentially getting rid of the biologicals at the same time. Also, as I said at the beginning, people buying ladybirds for everything. There is a specific predator for most pests, and with nematodes, people don't realise, until they go to buy the nematode, that a lot of them are pest-specific. It's the same with the crawling saviours. They are pest-specific, on the whole, as well, and you can't just buy the one that worked for your friend's plants because your friend might have had a different pest.

Andy: Yes. Maybe I should qualify what I've said. There's a lot of information out there on the internet, some of it's good, some of it's bad and it's finding a good, reliable source of information that's important.

Tessa: Yes.

Andy: A brand or a retailer that's recognised and has a good reputation and using what they say, rather than just what Joe Bloggs did.

Jane: Yes, there's a lot of people who just freak out so hard when they find a pest that they just want to kill it with fire, basically. The number of times I see somebody wanting identification for a pest, indoor or outdoor, and there's always somebody who replies with "Kill it with fire". I find that a really strange mentality, that anything that's living that isn't exactly where you want it, you want to destroy it.

Tessa: They seem to be the same people that then when you suggest introducing a mite, "Oh, I don't want those in my house!"

Jane: Is that a fear then? People think they're going to take over? That does seem to be a fear that people have. I want to tell them, "You do realise you have mites living on your face!?"

Tessa: Yes.

Jane: But that might blow their minds.

Tessa: Yes, especially with the questions that came up when you asked. There was two camps; there was one camp of people that didn't want more bugs in their house and were worried about them over-producing out of control and then the other camp wanted to work out how they could get them to reproduce and almost build their own biological control factory inside their house.

Jane: Which presumably is not possible? They're there for a set amount of time unless you want the three-storey fermenting tube?

Tessa: Also, you'd have to keep introducing pests for them to eat. You're introducing them to get rid of the pest that's attacking your plant. You don't want to rear more pests to eat your plants so that you can keep the biologicals alive.

Jane: I can see the flaw in that argument! That's a good point. Leave it to the professionals because it all sounds like it's very high-tech and not something that we can do at home. I guess what we should be concentrating on doing, is making sure that we read the packet and apply them properly because that is the best way of getting the best out of them, right?

Tessa: Yes, and if you're not sure - ask! If you're not sure what you've got, ask. If you're not sure how to use it, pick up the phone. Don't worry, there's plenty of people that are happy to help you identify your pest and help you to get rid of it too.

Jane: Once you've seen spider mites wandering about on a leaf, it suddenly focuses your mind that you actually do have a problem.

Tessa: Unfortunately, a lot of people don't realise they've got spider mite until they see the webbing, at that point you're quite far down. And then outside, the creatures that are nocturnal, for example slugs and vine weevil, which are the two pests that are the most prolific, they have different ways in which they eat your leaves, so you can look for the pattern by which they're munching in your garden.

Jane: I know those signs very well for the vine weevil.

Tessa: They turn your leaves into little jigsaw pieces.

Jane: They do and they're horrible! I guess sometimes, occasionally, people do manage to bring those inside if they've left their plants outside, they are really a pest of outside, but I imagine there'll be a few listeners who've had...

Tessa: Yes and they're often in your pots on your patio, so they'll have a little trip indoors.

Jane: Yes and those c-shaped larvae... they're quite satisfying, I've had the experience of lifting up a Heuchera and, literally, it coming away in my hand because they've eaten all the roots and then you've got to dig down...

Tessa: And then you find them.

Jane: Yes.

Tessa: When we were talking about prevention earlier, I think, with something like slugs or vine weevil, you don't have to worry about there being any of those pests - they're there. So getting that treatment down early in the spring to avoid problems later on is really important.

Jane: And I know slugs are really outdoor pests but I did, yesterday, turn over an Oxalis triangularis pot and discovered slugs hiding underneath and I thought: "That's why these leaves have been damaged."

Tessa: People tell me that they find slug trails on their stairs, people talk about barrier methods for slugs and crushing eggshells and putting various things around their plants to try and save them. For our wedding, we had tiny cactus plants as our wedding favours and I transported them all in the boot of my car, I left them in overnight, and lo and behold in the morning there was a slug trail across the top of the cactus plants. Yes, some of them really don't care about sharp stuff!

Jane: I always just say, if you feel like you're enjoying doing it, then do it, but otherwise it's really not worth the time. They will slime over anything, won't they, they really will!? Well, I think we've covered all the questions that we had from listeners. Is there anything else that we haven't discussed, that we need to squeeze in here, that might offer up any expertise for listeners on the wonderful world of biological controls?

Tessa: Andy touched on it slightly, about traps. I think it might be worth just mentioning the technology behind traps? For my customers and the people that I speak to, traps are great to help people with identification. So having a few sticky traps in amongst your indoor jungle is a good idea because it will give you early signal that there is a pest present and help you to identify it with your hand lens as well.

Andy: If you're looking at controlling within a household, in a small area, the traps will help with that management of the pest because you're taking out adults from the population, so it has two benefits.

Tessa: Fungus gnats, I would go nematodes and yellow sticky trap.

Jane: The one thing I find with those sticky traps is I end up sticking them to myself, my hair, any tips for actually getting them into situ, into place without getting yourself trapped?

Tessa: I would put them in place first or some people cut them up smaller and put them in place and then and then take the protective paper off.

Jane: Andy, why are they yellow? Is there a reason for that?

Andy: Yes, again, it goes back to the science that goes into these sorts of things which you might not really consider. Yellow has been identified, certainly for Sciarid Fly, for fungus gnats, as the colour the adults are attracted to. So depending on the pest, you'll have different colour traps. Yellow is the one you commonly find for household plants because the fungus gnat is such a problem, but if you go out into horticulture you have blue, white, black patterned, unpatterned...

Tessa: Red ones now, as well, for leaf hopper, and for thrips it's blue, so if people have got a thrips problem, it's a blue sticky trap.

Jane: That's fascinating. I've learned something new there!

Tessa: You should have watched David Attenborough last night. Zebras don't get flies on them like horses do because the flies can't work out where to land because of the black and white stripes.

Jane: Okay, I'm going to tell my horse-owning friends immediately to paint their horses with stripes. That is an amazing fact to finish on! Thank you both for joining me and for answering all those many questions and, hopefully, that's given us all a bit of an insight into how to use these biological controls effectively and to get the best out of them because they can save us from all kinds of infestation problems that we face. I know my listeners get very upset when their houseplants get infested with pests and damage, so it's good to know that there are controls out there that will really help out with this problem without causing too much damage to the environment, so thank you very much, both of you, for joining me, Tessa and Andy.

Andy: Pleasure, thank you, Jane.

Tessa: Pleasure.

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Jane: Do check out the show notes at janeperrone.com where you'll find information about the stuff we talked about in that interview including Bti, treatments for thrips and links to the Exeter University mealybug treatment on their Atriumtrees.

Now it's time for Question of the Week and the question comes from Claire, who has a question about a beloved Purple Shamrock. Purple Shamrock, well, that's Oxalis triangularis, although most of the time we forget to add on the last bit, which is subspecies papilionacea, obviously 'papillon' meaning 'butterfly'. Claire has found that her plant has been thinned out over the winter by losing some leaves. Don't worry, Claire, this is totally, totally normal for Oxalis triangularis. They do tend to go dormant in winter, or at least lose a certain amount of leaves. Claire is worried because some of the base of the plant is exposed and not covered in soil and she's worried that the stems being exposed is going to damage the plant in some way and notes, "Typically, everything else in my collection gets more rooted in compost." This is a great question, Oxalis triangularis grows from corms, which are a bit like bulbs except they don't have lots of different layers, and the corms are what makes this Oxalis quite so good because, if it does die back in the winter as they are prone to do, or indeed if you keep it outside you can grow this as an outdoor plant it will die back in winter and then revive itself, the plant is able to store resources in that corm and regrow, which is a pretty neat trick, I think you'll agree.

So how deep should these corms be buried in the soil? Oxalis is very, very easy going, so in many respects I'd say don't worry too much. I have planted them as much as five centimetres below the soil and not had a problem with them sprouting. I have also got some plants where the corms are right on the surface;‹ equally no problem. Generally, the rule with planting bulbs and corms is that the bulb or corm should be at least three times the depth of the diameter of the bulb. What that means is if you measure your bulb across, and it's a centimetre across, then it should be at least three centimetres under the surface, if not more. Why? Well, this helps the plant to be stable for the plant to develop a good root system, and for the corm or bulb not to dry out too quickly. In the outside world anyway, it would not be dug up too easily by any creatures that might have an eye on them, such as squirrels. As I say, in the house, they can be grown on the surface or near to the surface without too much of a problem. The main problem you're going to come across is that those stems aren't very well anchored into the soil. If this is a problem for your plant it's easy enough to solve, you just need to take the plant out of its pot, carefully tease out those corms with their attached stems - and be careful because they are quite fragile - and just replant them with more soil around the stems and you'll find that the plant will be absolutely fine, especially if you do it at this time of year when the plant is really starting to motor away and put on new growth.

If you don't have any Oxalis triangularis in your life, do go and listen to my special episode on this plant. It's a wonderful one and you can pick up the corms quite cheaply from garden centres and on places like eBay and other platforms. They're sold in packs for outdoor growing and that really is the cheapest way of getting hold of them. The most expensive way is by buying an established plant and if you're really worried about starting something off from a corm, of course, you can go down this route but you get much more for your money if you go down the corm route and, yes, it can also count as part of the On The Ledge Sowalong. Somebody messaged me the other day saying "If I plant these . . ." - it was either Colocasia or Caladium tubers - "Does that count for the sowalong?" to which my answer was, "Of course it does! That's absolutely fine!" So, do get hold of this plant if you can. There are other species of Oxalisthat you can grow. I really like Oxalis tetraphylla which is the Iron Cross Oxalis, which is a popular outdoor plant. There's also Oxalis corymbosa aureo-reticulata, with the beautiful network of yellow veins, which is very fun too.

If you are starting these plants off, just put them somewhere warm and sunny and you should find that they sprout soon enough. If you are sowing Caladium tubers this spring, as so many listeners seem to do, warning from me having had experiences with this in the past, make sure that you give them plenty of heat. Caladiums, they're tropical plants, they like lots of heat as opposed to the Oxalis which is a bit more of a cool temperate plant and isn't so bothered. Those Caladium bulbs, they need lots of warmth and heat, so put them on your sunniest windowsill and use a propagator for those, if you can. Jolly old Oxalis triangularis, shove them in a pot and they'll pretty much grow!

I hope that's helpful, Claire, and if you've got a question for On The Ledge podcast, drop me a line ontheledgepodcast@gmail.com is the address and be like Claire, Claire put a nice couple of pictures of her plant in and gave me lots of information, and that's what makes my job nice and easy! Let's wrap up the show with Meet the Listener and our listener this week is Tate.

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Tate: Hi everybody! My name is Tate, I'm 28 and I live in Sioux Falls, South Dakota, which is located in the north-central part of the United States. We experience a huge temperature change throughout the year and keeping houseplants is a great way to offset the winter here. During the day, I'm a section grower for a large wholesale greenhouse, which is over 20 acres of covered greenhouse space. We're the largest greenhouse in South Dakota. We grow exclusively for a large, orange big-box store here in the mid-west, focusing on spring bedding plants and perennials that are hardy to our general area of the country. It's so much fun to see the greenhouses fill up as the spring progresses. When I get home, I enjoy pottering around my large houseplant collection and the challenge of sneaking another in without my girlfriend noticing. I'm a big fan of Hoya, I like Staghorn Fern, orchids, Aroids and I've also really been interested lately in Epiphytic Cacti and Ant Plants.

Jane: Question one. You've been selected to travel to Mars as part of the first human colony on the red planet. There's only room for one houseplant from your collection on board. Which plant do you choose?

Tate: In the off event that someone let me on a spaceship, I'd bring a Monstera adansonii. It has proved to be such a resilient plant for me and is quite tolerant of neglect. I'd like to think it would make a great plant trade with a martian. Then again, this is why I probably wouldn't be allowed on the spaceship.

Jane: Question two. What is your favourite episode of On The Ledge?

Tate: On The Ledge has provided many excellent episodes and my favourite is the one with Tyler Thrasher. Tyler's been such an eloquent voice to help guide people through the nonsense of the last year. Not only has he been a pivotal voice in the plant community in 2020, but he is also an expert in many of the things he pursues. It's always so impressive to see every new endeavour that Tyler is posting about on Instagram and the wisdom that he's always talking about in his plant rants.

Jane: Question three. Which Latin name do you say to impress people?

Tate: Scientific names have a reputation as being difficult to understand, but it's not the case, and I believe that one of the best things you can do in your journey of knowing your plants better is to learn and use the scientific names. These names allow you to communicate with other people about these specific plants all across the globe, whether you're speaking English, French, Japanese, it's always going to be the same and, usually, these Latin names are going to tell you something about the plant. Sometimes it describes the location the plant is from, a notable characteristic, the person who first described the plant. Personally, one of my favourites that I like to tell people about is Begonia Darthvaderiana! Maybe some day I'll be cool enough to have a plant named after me!

Jane: Question four. Crassulacean acid metabolism or guttation?

Tate: Guttation is cool to see in action but, overall, I think that CAM is just much more interesting. CAM is such a specialty adaptation to survive an extreme environment and really, as a grower, I just see guttation as a symptom of over-watering, plus CAM is practiced by a number of species of Hoya which really are my favourite plant.

Jane: Question five. Would you rather spend £200 on a variegated Monstera, or £200 on 20 interesting cacti?

Tate: With the current plant prices, I don't know that I would get much more than a hunk of stem if I bought a $200 variegated M**onstera. I could probably find 20 interesting cacti and lately I've been quite interested in Epiphytic Cacti. I grew out some Pseudorhipsalis ramulosa from seed for the On The Ledge Sowalong last year and I plan to grow out more this year. Right now, I'm on the hunt for a Soft Tail Monkey Cactus or Hildewintera colademononis**. I think that the Epiphytic Cacti are so cool and I find it super-fascinating how they challenge all the concepts that you have as a keeper of cacti but it grows in the trees.

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Jane: Thank you, Tate! What I love about Meet the Listener is the diversity of the people who love this show. So why not put yourself forward? Drop a line - ontheledgepodcast@gmail.com - and my oh-so-efficient assistant, Kelly, will be in touch with instructions.

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Jane: That is all for this week's show and if anyone's desperate to know the colour of the walls in my front room, it's called Mineral Mist. I'm not sure if I want a mist of minerals on my walls but the colour is quite nice. It's pale blue, basically! That's all for this week, I will see you in exactly seven days' time. Bye!

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Jane: The music you heard in this episode was Roll Jordan Roll by The Joy Drops, Rashem Pidity, Pokhara by Samuel Corwin, Chiefs by Jahzzar and Sundown by Josh Woodward. All tracks are licensed under Creative Commons. Visit janeperrone.com for details.

Subscribe to On The Ledge via Spotify, Apple Podcasts, Player FM, Stitcher, Overcast, RadioPublic and YouTube.

Listen to the second part of my interview on biological controls for pests, plus I answer a question about an Oxalis and give an update on the sowalong, and we hear from listener Tate.

If you haven’t heard episode 176 yet, hold off listening and head over to part one of my chat about biological controls, which is here.

(If you want to check out the dryer rack you can hang on a window to display plants, as suggested by Scottish Plant Dad, here’s a couple of examples from Argos and Amazon.com.)

Amblyseius andersoni are supplied in slow-release sachets to treat red spider mite. Photograph: Ladybird Plantcare.

This week’s guests

Tessa Cobley of Ladybird Plantcare sells biological controls to UK gardeners for pest control on plants inside and outside. She is on Instagram as @ladybirdplantcare.

Dr Andy Brown is managing director of Andermatt UK. a manufacturer and seller of biological controls. Follow Andermatt UK on Twitter here.

Check out the notes below as you listen…

Mealy bugs

Brown Australian ladybirds (Cryptolaemus montrouzieri) can be used to treat mealy bugs, but they are best used in large greenhouses full of plants rather than a couple of plants. They need good light levels and a temperature of more than 20C.
When these ladybirds are used on larger plants, they are often contained with fleece to stop them flying away. Check out the University of Exeter’s use of Australian ladybirds as biological controls on trees in their atrium here on the university’s blog and also on Instagram.
For more on mealy bugs check out my episode on these pests here.

BTI

BTI stands for Bacillus thuringiensis subspecies israelensis: this is a biological control made from a group of bacteria that produces toxins which kill the larval stage of flies in the order Diptera, which includes fungus gnats, aka sciarid flies as well as mosquitoes. They are usually sold in the North American domestic market as Mosquito Dunks or Mosquito Bits.
BTI is not licensed for use in the UK so is hard to get hold of in this country, but it is seen as being a very safe product.
For treating fungus gnats, you can add the Bits to potting mixes when potting up.

Thrips

Thrips are another common pest of houseplants - there’s a good RHS page about thrips here.
Cucumeris (Neoseiulus cucumeris) - these predators come in slow release sachets and eat the larval stage of thrips
Amblyseius swirskii requires higher temperatures (20C) to work and also come in sachets, but it ins’t licensed for domestic settings (ie non-professional growers) in the UK. (You can see the full list of biological controls that are licensed for home/professional use in the UK here.)
Nematodes such as Steinernema feltiae can work on thrips in their larval form.
Orius (Orius insidiosus), aka the minute pirate bug eat all stages of thrips and are the most effective treatment. You can watch a video showing orius at work here.

Sticky traps vary in colour as different pests are attracted to different colours. Photograph: Ladybird Plantcare.

Scale

Scale insects can also be controlled using a foliar spray of nematodes.
I treated scale on my Pellionia repens with frequent sprays of SB Plant Invigorator.
While waiting for your biological controls to arrive, if you’re planning on using horticultural soap sprays or a product such as SB Plant Invigorator Tessa recommends stopping using such sprays the night before the biological controls are applied to make sure you are not killing off beneficial insects.

Mites - on my face?!

Yes. There are mites that live on human skin. More here, if you dare.

Sticky traps

These are useful for early warning about pests in your home, and can also help in terms of controlling the adult population of things like fungus gnats. The grid markings on many traps allow growers to keep an eye on numbers of insects caught. Different colours work for different pests depending on what colour the adult pest is attracted to - here’s a guide. Yellow for fungus gnats, blue for thrips, yellow patterned for whitefly and red for leaf hoppers.

Sowalong update

Thanks to all of you who are sharing your sowing successes (and failures!) on social media. Remember to include #OTLsowalong so I can spot your post and give you a shoutout on the show! Join Houseplant Fans of On The Ledge on Facebook to chat with other listeners about your seed sowing - remember to add OTLsowalong as a topic when posting.

If you haven’t listened to all the episodes talking about the sowalong, there’s a complete list here: and if you want to grow chillies indoors, do listen to my chilli episode too.

If you want to check out the cactus and succulent sowing leaflet I mentioned, it’s here.

QUESTION OF THE WEEK

Clare emailed about her Oxalis triangularis subsp. papilionacea, aka purple falseleaf shamrock. She was worried because the plant’s corms are close to the surface, and she wonders whether they should be planted deeper. The wonderful thing about this plant is how adaptable it is: normally when planting corms or bulbs, the rule is that they should be planted at least 3 times as deep as the diameter of the bulb/corm. I have buried Oxalis corms deep and left them almost on the surface, and they grow either way, but planting deeper does help to anchor the fragile stems of the plants, and also prevents corms from drying out.

The other Oxalis I mention as worth growing are Oxalis corymbosa ‘Aureoreticulata’ and Oxalis tetraphylla 'Iron Cross'.

Do listen to my Oxalis episode for more on these wonderful plants!

Want to ask me a question? Email ontheledgepodcast@gmail.com. The more information you can include, the better - pictures of your plant, details of your location and how long you have had the plant are always useful to help solve your issue!

HOW TO SUPPORT ON THE LEDGE

Contributions from On The Ledge listeners help to pay for all the things that have made the show possible over the last few years: equipment, travel expenses, editing, admin support and transcription.

Want to make a one-off donation? You can do that through my ko-fi.com page, or via Paypal.

Want to make a regular donation? Join the On The Ledge community on Patreon! Whether you can only spare a dollar or a pound, or want to make a bigger commitment, there’s something for you: see all the tiers and sign up for Patreon here.

The Crazy Plant Person tier just gives you a warm fuzzy feeling of supporting the show you love.
The Ledge End tier gives you access to two extra episodes a month, known as An Extra Leaf, as well as ad-free versions of the main podcast on weeks where there’s a paid advertising spot, and access to occasional patron-only Zoom sessions.
My Superfan tier earns you a personal greeting from me in the mail including a limited edition postcard, as well as ad-free episodes.

If you like the idea of supporting On The Ledge on a regular basis but don't know what Patreon's all about, check out the FAQ here: if you still have questions, leave a comment or email me - ontheledgepodcast@gmail.com. If you're already supporting others via Patreon, just click here to set up your rewards!

If you prefer to support the show in other ways, please do go and rate and review On The Ledge on Apple Podcasts, Stitcher or wherever you listen. It's lovely to read your kind comments, and it really helps new listeners to find the show. You can also tweet or post about the show on social media - use #OnTheLedgePodcast so I’ll pick up on it!

CREDITS

This week's show featured the tracks Roll Jordan Roll by the Joy Drops, Chiefs by Jahzzar, Rashem Pidity, Pokhara by Samuel Corwin and Sundown by Josh Woodward.

Pests & diseasesJane PerroneMarch 19, 2021Oxalis, fungus gnatsComment