Episode 102: spider mites

Red spider mites suck the sap from the undersides of leaves. Photograph:  Gilles San Martin  on  Flickr .

Red spider mites suck the sap from the undersides of leaves. Photograph: Gilles San Martin on Flickr.

Red spider mites may not be visible with the naked eye, but they damage they can do to our houseplants is considerable. I get an insight into the world of the spider mite with entomologists Jules Howard, who is the author of books including Death on Earth; and Andrew Salisbury, who is principal entomologist for the RHS, and look into the various options to keep mites under control. And I answer a question about easy trailing plants that are non-toxic to cats.

Check out the notes below as you listen to find out more about the fascinating world of mites, and how to control the red spider mite.

Spider mite specifics

  • The red spider mite, Tetranychus urticae, is also known as the two spotted spider mite.

  • its lifecycle lasts only up to a month: check out this video for a look at the spider mite all stages. The RHS has an excellent information page on red spider mite that is worth checking out too.

  • The red spider mite is the main mite that will attack houseplants, although the mite family is enormous. (Patreon subscribers of $5 a month or more can hear more mite insights from Jules Howard in An Extra Leaf 30).

  • It seems to favour papery-leaved plants of the Maranta group but can attack just about any houseplant.

Spider mite symptoms

  • The first signs of an infestation are the plant starting to droop and generally look miserable.

  • The leaves will develop pale mottling as the mites begin to suck sap from the plant cells.

  • The undersides of the leaves will display a grainy white substance, and more severe infestations may exhibit webbing.

  • The leaves will eventually turn yellow and die off, leading to total plant collapse.

Treating spider mite

  • Prevention is better than cure: making sure your plants are in good health will help prevent pests from taking hold. Pests tend to target specimens that are already undergoing stress: they love hot, dry conditions so are a particular problem in summer.

  • When it comes to pesticides to treat red spider mites, Acetamiprid is a systemic pesticide that is suitable for use on houseplants, although I don’t use it because I take an organic approach. Acetamiprid contains neonicotinoids which have been linked to bee decline.

  • Neem oil is a popular treatment for spider mites and other houseplant pests: however it is not licensed for use as a pesticide in the UK so I don’t use it. It is meant to be effective, but if you use it, please don’t assume that because it’s “natural” (it is extracted from the neem tree, Azadirachta indica) can be sprayed indiscriminately: you still need to follow the instructions closely.

  • There are a number of pesticides available that are based on plant oils or fatty acids: they work really well, but may need repeated treatments to work fully.

  • There are a number of ‘plant invigorator sprays’ on the market which contain a mix of nutrients and surfactants, such as SB Plant Invigorator, Neudorff Plant Invigorator and Ecofective Houseplant Defender.

  • When you first see spider mite symptoms, isolate your plant, and start treating it immediately. Washing or wiping down with a damp cloth daily will help remove mites and eggs: focus on the underside of the leaves.

  • Biological controls such as the predatory mite Phytoseiulus persimilis are best used early on in infestations, and for larger collections.

My Pilea libanensis, as mentioned in episode 99. Photograph: Jane Perrone

Question of the week

Charlotte wanted some recommendations for trailing plants that are easy to grow, not too common, but non-toxic to cats. There’s a great list of cat-safe plants here, but trying to find ones that are easy and yet not common is a bit trickier.

I suggest foxtail fern, aka Asparagus densiflorus 'Myers', which isn’t actually a fern but is easy to grow and very elegant; the old school yet wonderful Cissus rhombifolia aka grape ivy, trailing members of the Pilea and Peperomia genera including Pilea libanensis and Peperomia quadrangularis, and (if there’s plenty of sun, burro’s tail aka Sedum morganianum.

For more information on cats and plants, check out On The Ledge episode 40.

Want to ask me a question? Tweet @janeperrone, leave a message on my Facebook page or email ontheledgepodcast@gmail.com.


If you are in the Glasgow area, listener Steve tee is planning a meetup! Join the Facebook group or contact me to get involved.

There’s a London Plant Crawl happening on July 28 - details here.

Join me at Lullingstone Castle in Kent in the UK on September 21 and 22 2019 for Cactusworld Live where I’ll be doing a live recording of On The Ledge and holding a listener meetup.

The following weekend I’ll be at the Garden Museum on Sunday September 29 for their Houseplant Festival: I’ll be helping out with the houseplant clinic, and there’s also the chance to take part in workshops and browse an awesome range of stalls from some of my favourite houseplant shops!



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Beet ‘Red Detroit’ microgreens seeds from  True Leaf Market.

Beet ‘Red Detroit’ microgreens seeds from True Leaf Market.


Thanks so much to True Leaf Market for backing On The Ledge for three whole months. This Utah-based seed company has been helping gardeners grow since 1974, so what they don’t know about sowing and raising healthy plants - well, it’s probably not worth knowing!

if you’re growing herbs - whether on the ledge or in the garden - true leaf market makes it easy as ABC to find the seeds you’re looking for - that’s anise, basil and cilantro of course. 

Their easy to use website features everything from LED growlights to wheatgrass kits, plus a great range of flower and veg seeds and microgreens seeds, like these ‘Detroit Dark Red’ beet seeds. You’ll enjoy lightning-fast shipping and a 30 day satisfaction guarantee.

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This week's show featured the tracks Roll Jordan Roll by the Joy Drops, InsectifEYE by KidNNasty and Lonely Spider by Cullah. Ad music is by the Heftone Banjo Orchestra:  Dill Pickles and Whistling Rufus. All tracks licensed under Creative Commons.

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