Usually, when you ask a plant person what to use to kill just about any kind of houseplant infestation, they’ll tell you to opt for neem oil. But rarely does this advice come with instructions or precautions. So, what is it, and how can it help your houseplants thrive?
The short answer is this: it’s an organic, biodegradable, plant-based pesticide and fungicide that’s safe to use indoors and can help keep your houseplants healthy. If you’re curious to learn more, though, read on to find out what exactly neem oil is and how you can use it to help your houseplants reach their full potential.
What is Neem Oil?
Neem oil isn’t another one of those diluted, spray-on, cure-all solutions to common houseplant pests and infestations. On the contrary; it’s a naturally occurring compound that is extracted from the Azadirachta indica plant, which is an ornamental tree that’s native to South Asia and India. It’s a fairly common plant and has been historically used in the preparation of everyday goods from waxes to old-world remedies.
More recently, neem oil is widely distributed and sold in large volumes all the way up the supply chain, from nurseries and big box stores to industrial suppliers. Typically sold in a plastic jug, neem oil is rather inexpensive, and is a great alternative to more synthetic chemical-based pesticides., as it’s both organic and biodegradable.
While it doesn’t directly kill ailments such as viral and bacterial plant diseases, it can absolutely help to prevent the vectors that carry them, such as flying pests and contaminated watering cans. Neem oil does kill many pests, however, by a variety of means that depend on which kind of bug you’re dealing with- and all without harming you or your pets.
Neem oil is a marvelous organic pesticide; although it might smell like a chemical derivative, the oil itself is extracted from the plant and is often mixed with water and castile soap to thin it down to a sprayable consistency. It’s incredibly popular in organic vegetable gardening and as a pest repellent in herb gardens and orchards.
Although neem is incredibly efficient on its own, it’s also added to chemical pesticide mixtures and sold as a broad-spectrum solution and preventative treatment, which is intended to be more effective than neem oil alone. However, keep in mind that these mixtures are generally produced using chemicals that are not safe to use indoors.
Many fungi survive by sapping energy and nutrients from houseplants, which are considered “hosts” for these invasive mycotoxins. As a preventative measure, neem oil can help protect your houseplants from a variety of fungi, from leaf spot to powdery mildew, but may not be as effective for severe cases of stem rot or root rot.
More often than not, fungal infections are present in houseplants before you can see them; after all, they’re microscopic organisms that multiply over time, depending on the species. So, if you happen to notice your houseplant barely hanging on for dear life, the best recourse is to get rid of it before it infects nearby plants- and to treat those just in case the fungi was spread by a vector you commonly use, such as pruning shears or a moisture meter that contacts soil.
Neem oil isn’t for use on every type of houseplant, though. Houseplants that have hairy, velvety, or even dimpled leaves or stems won’t be helped by neem oil, since the oil simply sits on top of these features. Instead of being stuck in the oil, the pests can simply hide underneath these spines (or little hairs) and continue to affect the plant.
In the case of a soil-centric issue, such as root rot or fungus gnats, neem oil can be used a soil drench. However, since the neem oil can suffocate roots alongside pests, it’s best to reserve this treatment as a last resort. Most of the time, however, a neem oil soil drench is a one-and-done deal, and should successfully eradicate soil-dwelling invaders when applied properly.
A soil drench with neem oil should be more diluted than a typical neem oil spray application- for every gallon of water, add a teaspoon of castile soap and a tablespoon of neem oil, mixing well before watering. Place the plant in a large, empty bowl or drip pan, then slowly pour the mixture over the soil until it becomes entirely saturated. Allow the plant to sit in the container for 15 to 20 minutes, then remove it and allow the excess solution to drain away from the pot.
This process can be repeated weekly until soil-dwelling pests like fungus gnats are gone, or as a preventative solution every two weeks for plants recently rehabilitated from root rot to prevent a re-infection. It can take time for pests below the surface to completely disappear, so don’t give up hope after only a couple of treatments.
Safety & Precautions
While neem oil is generally considered safe for use around humans and pets, it can be irritating to the skin and stomach, though this is rare. Best practices are to avoid direct contact with concentrated neem oil on the skin, and to avoid accidental ingestion of neem oil. Neem oil may also be harmful to pregnant or breastfeeding women.
Aside from the general safety precautions, neem oil is also quite smelly! Some like the scent, but it can seem especially strong to some and can linger in an unventilated area. We recommend using neem oil outside if possible until it dries, or using it without a spray bottle indoors without ventilation.
That being said, neem oil can really clog up a spray bottle if left unmixed for long periods of time. Try to only mix as much as you need, then thoroughly clean out your bottle with warm water and castile soap until the sprayer has been thoroughly rinsed out-meaning you can’t see any traces of neem in the tube.
Another quick point to be aware of is that neem amplifies the sun’s rays on plant leaves. So, if you happen to keep your houseplants near a bright, sunny window, try to keep them further away or out of direct sunlight for a few days after applying neem to above-ground parts of the plant. If you notice leaf tip yellowing or sun spots, try placing the affected plant in a window that has lower light.
When to Use Neem Oil
It’s time to break out the neem and go to work as soon as you discover an infestation or disease. While neem oil can’t solve every last problem your plant may have, it can certainly help to reduce the prevalence of most planty invaders, from plant viruses and bacteria to fungi and pest insects.
Most houseplant keepers notice an issue with one or two plants at a time, but that’s usually just the tip of the iceberg. If you use any kind of tools- such as moisture meters, shears, and even planter decor that’s moved around- you could accidentally spread infestations from one plant to another. That being said, it’s a good idea to treat all your houseplants along with the affected ones, and to keep up on general anti-pest maintenance.
Pests can enter your home in a number of ways, too. A simple hike on a woodland trail or walk through a park heavily decorated with trees and shrubbery can allow you to pick up all sorts of insects and microbes, which in turn can spread from your clothing or hands to your plants. As annoying as this sounds, you can avoid this by refraining from plant care until you’ve washed up after being outdoors, and by using a light neem oil treatment routinely to further protect houseplants.
Treating Pests With Neem Oil
There’s nothing quite like the dread that comes with finding a pest infestation on one of your beloved houseplants, and we all ask ourselves that question: “is it worth it to save my plant?” The answer is yes, so long as you catch the infestation before it becomes too severe. Infestations like scale and spider mites can quickly kill a houseplant, so get ahead early.
Ideally, you need to use a slightly stronger neem oil spray twice per week to get rid of a difficult infestation. Some pests are trickier to eradicate than others. Scale, for example, is painstakingly difficult to get rid of, and in most cases needs to be removed by hand with an alcohol swab. However, neem oil is a great option for most pest issues.
Common Houseplant Pests:
To treat an infestation in its beginning stages, use neem oil once per week to kill of adult insects and to prevent their eggs and larvae from maturing. Neem can kill bugs in all stages of growth, but it isn’t uncommon for a few stragglers to persevere. For just a few mild spots, treat once per week, covering the affected areas in a spray.
However, if you’re dealing with something that spreads fast and takes no prisoners, you might need to ramp it up to twice a week, adding a tad more neem oil to your mixture than normal. Be sure to thoroughly soak the entire plant and then some, just to be certain. It helps to use gloves to physically remove as many creepy crawlies as possible before spraying.
Here’s how to mix a neem oil spray to treat houseplant pests:
Mix together in a spray bottle the following ingredients:
- 3 cups warm water
- 2 tablespoons clarified hydrophobic neem oil
- 1 tablespoon castile or plant-based dish soap
Shake the ingredients together in your spray bottle very well. Remember that neem oil can’t be stored in a spray bottle once it’s mixed, and will deteriorate very quickly, which will render your spray bottle useless and unsalvageable. Clean out or use up any excess spray after use; you can even spray out the rest in flower beds or nearby your windows to repel other insects.
Treating Microbes With Neem Oil
Microbes include everything from fungi and bacteria to plant viruses (which are extremely rare in captivity) and other contagious diseases. There’s no shortage of infectious plant diseases and another immeasurable number of them out there that haven’t been discovered yet. Here are a few of them that you might find on a houseplant.
Common Types of Fungi and Bacteria:
- Leaf spot
- Sooty mold
- Stem rot
- Black spot
- Powdery mildew
A foliar neem oil spray for fungal issues that affect the parts of the plant above the soil surface should be applied heavily on every surface of the plant once every one to two weeks. The oil sits on the surface of the invader, suffocating it and preventing any new growth. After that, use a maintenance mixture every month or so to keep microbes from sneaking back in.
Here’s how to mix a neem oil spray to treat houseplant diseases:
Mix together in a spray bottle the following ingredients:
- 3 cups warm water
- 1 tablespoon clarified hydrophobic neem oil
- 1 tablespoon castile or plant-based dish soap
Shake the ingredients together in your spray bottle very well. Remember that neem oil can’t be stored in a spray bottle once it’s mixed, and will deteriorate very quickly, which will render your spray bottle useless and unsalvageable. Clean out or use up any excess spray after use if you plan to use it again..
Neem oil can also be used in place of a standard leaf shine spray, which can clog the delicate pores of plant foliage that are responsible for the exchange of gasses. This is an issue because plants need to “breathe” in a sense, and most leaf shine is made from heavy oils and waxes, which happen to attract more dust and dirt and ultimately dampen the effectiveness of the whole photosynthesis process.
When using neem oil to make a mild leaf shine, you should really only use a tiny amount- especially if you’re not the best at keeping up on houseplant dusting. Another thing to consider is the smell of neem, which can be a bit overwhelming in enclosed spaces- best to use a neem-based leaf shine outside, where it has a chance to disperse in the breeze.
To make a neem oil leaf shine spray (or wipe-on compound), simply add a tablespoon of castile soap or plant-based dish soap, one tablespoon of clarified hydrophobic neem oil, and three cups of hot water to a spray bottle. Mix well, then allow the mixture to cool to room temperature before re-mixing and spraying.
Be sure to use a soft cloth to remove excess spray and leave a shiny, gleaming finish over your plants’ leaves. If you skip this step, you risk clogging precious leaf pores and subjecting your houseplant to leaf drop and stunted growth, among other things.
Neem oil should be used once per month as a preventative measure and to maintain healthy, clean leaves, but a simple dusting twice per month can help to remove stomata-clogging dust and give you a close-up look at your houseplants, which can help you notice pests and infestations before it’s too late.