When and How to Use Neem Oil to Control Pests

When it comes to natural pesticides, neem is something you’ll want to have on hand. Neem oil, extracted from the seeds and fruit of the neem tree, has multiple uses in the garden. Not only does growing a neem tree provide lovely sights and scents, but it also offers an excellent nitrogen booster for soil in the form of neem seed. You can even make your own neem oil.

Fortunately, you don’t have to go that far to use neem oil spray on your plants. This plant-based pesticide is widely available at big-box stores, online retailers, and small local nurseries. Safe to use up to harvest day, it effectively controls over 200 types of insect pests and serves as a biofungicide.

We consider it a gardening staple and highly recommend trying it out in your own gardening efforts!

What Is Neem Oil?

Neem oil comes from neem trees (Azadirachta indica), a widely cultivated species in tropical climates around the world. The seeds and fruits are pressed to extract the vegetable oil known as neem oil. Seed oil can range in color from yellow to brown or even a vibrant red. It has a pungent odor, often described as a mix of peanuts and garlic with a slightly sulfuric undertone.

Neem products typically combine neem oil with a surfactant, which helps disperse the oil and activate it for use on plants. However, neem oil itself does not mix well with water. The fatty acids in the oil, known as triglycerides, possess insecticidal, bactericidal, antiviral, and fungicidal properties. This makes it a valuable tool for organic gardeners, especially for controlling pests such as aphids, mealybugs, mites, thrips, and whiteflies on contact.

Clarified hydrophobic extract is a derivative treated with alcohol. This refined form is particularly effective against soft-bodied insect pests like aphids and mealybugs, as well as fungal diseases such as mildew and rust.

How Does Neem Kill Insects?

The naturally occurring chemical azadirachtin is the main active ingredient in neem oil products. In combination with other active compounds, azadirachtin induces anti-feeding behavior in soft-bodied insects. It also acts as a hormone disruptor, preventing normal growth and development in harmful pests.

Neem oil is effective at all stages of insect growth, killing eggs, larvae, nymphs, and adults alike. This broad effectiveness is why sprays are even used in some countries to control fleas on cats, a testament to how safe and effective it is.

How Does Neem Treat Disease?

While neem oil has strong insecticidal properties, it is also effective against bacterial and fungal diseases. Additionally, gardeners can use it to help prevent the spread of viral disease vectors.

While it does not cure diseases outright, it limits their proliferation and reduces the likelihood of further spread. In fungal infections, it prevents spore germination and stops spores from penetrating leaf tissue, making it particularly useful for treating powdery mildew.

Neem oil is also effective in preventing fire blight, a highly infectious bacterial disease that affects fruit trees in the Rosaceae family. Because this insecticide kills pests, it helps reduce the spread of viruses they may carry. While its direct antiviral properties remain under debate in peer-reviewed studies, an integrated pest management strategy that includes neem oil can be highly beneficial for controlling diseases in ornamental plants, indoor plants, and garden plants alike.

Benefits Of Using Neem Oil

Neem oil pesticides are not only effective, but they’re also generally recognized to be non-toxic to only slightly toxic by the Environmental Protection Agency and the National Pesticide Information Center. It does not harm birds, mammals, bees, and plants.

You can use neem oil to control insects like Japanese beetles, other beetle larvae, leafhoppers, spider mites, thrips, and aphids. As you spray to kill pests, you’ll also shield the entire plant from the harmful effects of some diseases.  

Neem oil also has a residual benefit for soil health, particularly in supporting earthworms, making it a safe choice for gardeners. This is because it is derived from neem cake, the solid mass of seeds and fruit left after oil extraction. Neem cake is commonly used to amend and condition soil, providing a rich source of nitrogen that many other amendments can’t match.

While some pesticides can have toxic effects on beneficial insects and soil health, even when applied in small areas, this oil protects plants at both the foliar and soil surface levels without harming the garden’s beneficial organisms.

Drawbacks Of Using Neem Oil

While pure neem oil has many benefits, improper use can be harmful to plants and beneficial insects. As with other pesticides, it’s important to wear protective gear when applying. The concentrated form can irritate the skin and sensitive areas like the eyes and lungs. If using wettable powders, pour carefully to prevent blowback and inhalation.

Children are more sensitive to neem oil than adults, so it’s best to keep it out of their reach. While irritation is typically minimal, it should also be kept away from pets. Additionally, it is slightly harmful to fish and amphibians, so using it on aquatic plants in areas where these animals are present is not recommended.

When used properly, neem oil poses no risk of skin irritation and does not harm beneficial insect populations, birds, or the surrounding environment.

How to Use Neem Oil

Always check the product label carefully before using neem oil. Put on gloves and protective eyewear if you know you risk making contact.

Mix

Cold-pressed neem oil needs to be mixed in a spray bottle before application. Start by combining a drop or two with a small amount of liquid to test. Add commercial insecticidal soap to help emulsify the oil and improve its effectiveness.

Keep in mind that neem oil breaks down within 8 hours, so only mix as much as you need for immediate use.

Spray

If you’re spraying an indoor plant, move it to an area where neem oil won’t irritate children or pets. First, test the spray on a small section of the plant to ensure it won’t cause burning. Always apply at dusk or just before sunrise. After spraying a small area, wait 24 hours to check for any discoloration or damage. If no issues appear, you can proceed with a full application.

Mist the plant leaves, starting from the bottom leaves and working upward. Ensure the undersides of the leaves are coated, as this is where most insect pests feed. Avoid drenching the plants and apply a light mist instead. Follow up with another application in 7 to 10 days, as repeated treatments are necessary for neem oil to build up effectiveness.

Pure neem oil can also combat fungi and bacteria that cause plant diseases. For fruit trees, spray every two weeks outside the blooming season until bud break, then pause and resume after the flowers drop. While neem oil creates inhospitable conditions for fungi like powdery mildew, it also helps prevent bacterial infections and insect-borne diseases. On fruit trees, aphids and mites are common issues, and using organic neem oil preventatively provides multiple benefits.

Soak the Soil

Another effective, non-toxic way to keep insects and other pests from feeding on your plants is to soak the soil. Prepare an organic neem oil pesticide the same way you would for a foliar spray, then pour 2 to 3 cups of the mixture around the base of each plant. Repeat this process every 2 to 3 weeks until insect activity decreases or disease symptoms improve.

Neem oil takes at least two weeks to take effect in the soil. For preventative control, apply a soil soak every three weeks throughout the planting season to help manage pests and diseases before they become a problem. Adding a bit of neem seed meal around your plants can provide a similar protective effect!

Winter Treatment

You can also use neem oil as a natural insecticide to treat plants affected by pests that overwinter in your garden. Some insects lay eggs on fallen leaves, which remain in the soil until the next season. A neem oil spray can help control moth larvae and pests like spider mites, which lay eggs that survive the cold and hatch when the weather warms.

One important note: if your plant is already stressed, avoid applying straight neem oil. Even though it is organic and relatively non-toxic, a plant weakened by insects or disease may experience additional stress from neem oil treatments. This applies to both soil soaks and foliar sprays.

A Word On Pollinators

Many people express concern about the potential risk neem oil poses to bees and other pollinators. While many pesticides do threaten pollinators, neem oil insecticide does not, if used correctly. As gardeners, we should take care to protect pollinators while still using neem oil effectively for pest control.

One way to do this is by avoiding excessive application. Light mists dry within 45 minutes to an hour, as neem oil’s moisture dissipates quickly when mixed with water. To protect pollinators, spray plants either early in the morning before they emerge or in the evening after they have returned to their hives and homes.

In a soil drench, neem oil has a half-life of 3 to 22 days, which is why it’s best to wait three weeks before reapplying. Pollinators are typically most active after sunrise and before sunset, so applying neem oil outside these hours helps ensure their safety. Butterflies, ladybugs, and lacewings don’t feed on plant matter, so as long as the neem oil mist has evaporated, they remain unaffected.

Frequently Asked Questions