does neem oil work on house plants?

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I think neem oil does work, and I don’t care if you think that I’m deluded.

Pest control is a bit of a contentious issue in house plant circles because what works for some people doesn’t for others.

A couple of years ago, neem oil was what we all used. There wasn’t really much else that didn’t require you to wear a mask or could only be used five times before it killed your plants.

And then systemic pesticides came about. You could pour then into the soil, the plants would take them up, and pests would be poisoned when they ate them

I’m sure they’re all very good, but YOU CAN’T GET THEM IN THE UK.

There is a couple of brands, but I’ve tried them and they, er, don’t work. At least, they didn’t for me.

The most upsetting thing in this whole debacle is that now a lot of people are not only claiming that systemic granules are better than neem oil (I can’t get them! I don’t want to hear it!) but also that neem oil is snake oil and it doesn’t work!

Arguments like this always pique my interest because I advocate for neem oil on this blog.

I recently saw a reddit thread where people were laughing at people for using neem oil.

I immediately made up a spray bottle of it, and sprayed down the Plague Plants*

*The Plague Plants are the ones that live in the bathroom that are constantly infested with thrips. Most plants cycle in and out of the infectious diseases unit, but there are a few that can’t shift em.

I diligently sprayed down my Phildeondron Pink Princess every five-ish days with neem oil, and wiped off any adults/larvae as I saw them. After about three weeks, the thrips were gone.

NEEM OIL WORKS.

Even on thrips, which become resistant to almost every other pesticide in general.

How does neem oil work?

Neem oil can’t kill on contact (unless you make up a really thick solution), but over time it messes up the hormones of bugs and makes them behave in ways that…don’t benefit the pest population.

  • They forget to eat
  • The females don’t lay eggs
  • Eggs don’t develop properly
  • Adults are sterilised
  • Disrupts sexual communication

Neem affects different bugs in different ways. It doesn’t, for example, have that much of an effect on adults BUT it inhibits the development of the larvae. If you’re treating thrips with neem, check your plant thoroughly and squish any adults yourself.

How to use neem oil

Neem oil needs to be made up fresh every time, or at least re-emulsified. It’s solid at room temperature, so you need to add it to warm water, or add more warm water to liquify it again.

I use a 300ml spray bottle, add in a pea-sized (ish) dollop of neem oil and top with warm water. I sometimes add in a drop of washing up liquid (dish soap) if I’m feeling fancy.

Another benefit of using warm water is that it’s less likely to leave white marks on the leaves than cold water. I have no idea why that’s the case, but that’s what some dude on the internet told me.

Before spraying, check the plant over and remove any bugs you can see. Then simply spray the plant down with the neem oil spray. If your plant sits in a sunny spot, keep it out of the sun until the plant dries off, otherwise, the combo of oil and water can make it more susceptible to burning.

Repeat weekly. You could probably go as frequently as every four days, but if you over neem, you can end up damaging leaves.

How long does it take for neem oil to work?

This will vary from plant to plant, and depend on how bad the infestation is.

If you’re consistent, you should see results in a month or so, but some plants may need ‘neeming’ for a lot longer.

I feel like I’ve mentioned thrips a lot (here’s a full guide to the little buggers), but that’s because I’ve found that they’re the most tenacious and difficult to get rid of. Sometimes they simply WON’T GO.

I can only assume they’re hiding the soil, so if I’m finding them especially tough to shift, I put diatomaceous earth on top of the soil so they can’t creep back onto the plant.

I have a post on diatomaceous earth here, but you simply sprinkle a layer on top of the soil. It has to be dry to work, so add it after you’ve neemed.

How often should you apply neem oil?

If you have a plant that’s infested with pests, spray it down with neem weekly. If you remove as many as you can before you spray it the first time, you shouldn’t need to apply more than that.

What plants should you not use neem oil on?

There aren’t any specific plants (that I know of) that can’t tolerate neem. A lot of people recommend not using it on plants with velvet leaves, but I’ve sprayed my Calathea velvet touch a LOT and she’s fine.

If you’re worried that neem will damage a plant (it’s never happened to me, but be cautious with pricey plants) then try it out on an inconspicuous leaf first.

Just make sure not to spray it on a plant and then leave that plant in direct sunlight, because sun and neem can causing burning.

Also, don’t use neem on outdoor plants, because it can harm beneficial pollinators.

Can you use too much neem oil?

You can definitely treat your plants too frequently. There’s not much benefit to spraying them more than every week – spraying them thoroughly less often is better than half-assing it every day.

The damage you can do will vary from plant to plant, but you can end up with brown spots on the leaves.

Don’t use more than a pea-sized amount of neem. If it’s too thick you’ll end up with an oily film over the leaf which can block the light and stomata, which would…not be good.

In conclusion

I think neem oil works. It’s not the fastest or the most effective treatment BUT it’s easy, relatively cheap, and it’s not as toxic as a lot of other big sprays.

My favourite type of pest control is using predatory bugs, but there aren’t that many available in the UK that aren’t extortionately priced. Neem oil works well if you’re consistent with treatment.

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