How to Properly Emulsify Neem Oil & Make a Safe Garden Pest Spray

Last Updated on September 1, 2022

Neem oil can be a great, non-toxic, useful product to protect your plants from pests or disease. That is, when it is mixed and applied properly! The big issue is that oil and water don’t easily mix, and most people don’t realize how to do this. When neem oil is not fully emulsified, is used in excess, at the incorrect time, or in the wrong situation, it can actually do more harm than good!

If you are here, researching how to mix neem oil, chances are you may already be somewhat familiar with neem itself. Just in case you aren’t, let’s briefly go over what neem oil is, how it works, and what pests it fights. Then I will show how to properly emulsify concentrated neem oil in water, to create an effective and safe spray solution to use in your garden.

What is Neem Oil?

Neem oil is a plant-based concentrated oil, extracted primarily from the seeds of the India-native neem tree. The oil is then diluted and mixed with water, and applied to plant foliage as an organic pest control. Cold-pressed extractions yield the highest quality virgin neem oil, and contain all the desirable active constituents. That is what we use! Check out our favorite cold-pressed neem oil here. In addition to being a natural, mild insecticide, neem also has healing medicinal properties and is commonly used in personal care products for people.

“Neem oil is made of many components, including Omega 3, 6, and 9 Fatty Acids. Azadirachtin is the most active component as a pesticide. It reduces insects ability to feed, and acts as a general insect repellent. It also interferes with insect hormone systems, making it harder for insects to grow and lay eggs. Azadirachtin can also repel and reduce the feeding of nematodes.” 

Oregon State University

“Neem oil” is sold either as concentrated 100% pure neem oil, a concentrated neem oil containing other ingredients, or pre-mixed, ready-to-use spray. Personally, we prefer to use the 100% pure stuff and mix our own. It is the most cost-effective and safe. Furthermore, one pre-mixed neem oil product line was recently found to be contaminated with several synthetic, non-organic pesticides that weren’t included on the label, including Malathion, Chlorpyrifos, and Permethrin! Yuck.

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About Neem Oil Safety

As moderate health-nuts and toxin-phobes here, we have done quite a bit of research on pure neem oil. Studies show that the only risk of acute harm to mammals or humans is if they’re exposed to very high concentrations of undiluted neem oil. Even with prolonged ingestion of high doses, the internal damage caused typically heals once the exposure is removed!

When applied correctly (follow instructions!) dilute neem oil is non-toxic and safe to use around humans, birds, pets, mammals, and most wildlife. Neem is not carcinogenic, and no chronic health effects from exposure have been found. However, neem concentrates can be slightly toxic to fish and amphibians, so extra precaution should be taken around aquatic environments.

What types of pests or diseases are neem oil effective against?

Neem oil is particularly effective against small soft-bodied insects. Examples include aphids, thrips, spider mites, mealybugs, scale, and white flies. When applied directly, the oil can coat their bodies and kill them – or otherwise interfere with reproduction and feeding. It is also said to repel mosquitoes, flies, cabbage white butterflies, and moths.

On the other hand, neem oil is not toxic to bees when used correctly! It also doesn’t bother other beneficial insects like ladybugs, earthworms, parasitic wasps, spiders, or adult butterflies – as long as they aren’t directly sprayed with it! Therefore, take care to spray it only in the evening hours, when beneficial insects are least active. Note that neem doesn’t do much to control caterpillars, except maybe repel their adult butterfly or moth form.

Additionally, that protective shine that neem oil adds to leaves makes them less susceptible to fungal diseases like powdery mildew, rust, or blight. It can help prevent fungal diseases from occurring, or slow their spreading, but is only marginally effective at treating an outbreak once established.

Using Neem Oil in the Garden

In our experience, neem oil is does a great job at preventing pest issues, and deterring pests. However, if you have a full-blown infestation of something like aphids, or a serious case of powdery mildew, we have not found neem to be very successful at bringing something back from the brink of death. Therefore, it is often recommended to apply neem oil sprays as part of a preventative care routine – for plants that you know are prone to issues. Or, start neem oil applications at the first sign of disease. Catch it early!

As a pest infestation or disease progresses, neem can still be used in conjunction with other pest control methods to bolster the effort, but may not be able to combat it on its own. Learn more ways to prevent or treat powdery mildew organically in this article, and 25 other organic methods to battle common garden pests here.

How we use neem in our garden:

In our garden, we don’t use neem oil heavily, though we do have a handful of pest-prone plants that appreciate a routine neem spray. For example, on artichokes. They’re total aphid-magnets, and also get powdery mildew very easily! Our citrus trees and passionfruit vines are commonly affected by mealybugs. Even though we also release predatory beneficial insects on those plants, an occasional neem spray helps knock the population back. Most often, we use neem on our cannabis plants, but only before they begin to flower. To read more about our cannabis pest control routine, see this post!

On the other hand, we use very little neem oil on short-lived plants in our vegetable garden. One, because as I stated: it isn’t a total problem-solver. Two, a lot of what we grow are leafy greens… I am not a fan of using neem oil on vegetation that I am going to consume, like kale, swiss chard, or lettuce. It leaves a bit of an oily residue behind that can be difficult to wash off. However, for the leaves of squash plants, tomatoes, cannabis, or other foliage we aren’t going to directly consume, it is a good product to keep in your pest control toolkit!

And now, what you came here for…

HOW TO MAKE NEEM OIL FOLIAR SPRAY

Ingredients 

• One gallon of water
• 1 tablespoons of concentrated, cold-pressed neem oil
• 1 teaspoon liquid soap OR 1 teaspoon pre-wetted silica powder, explained below
• Optional: 1/8 to 1/4 teaspoon aloe vera powder (recommended for cannabis plants) and/or a few drops of essential oils
• Scale all ingredients up or down evenly as needed

Unfortunately, you can’t just mix all of these things together in your pump sprayer and go to town. Just as we all learned in elementary school science class: Oil and water don’t mix. Or at least, not easily.

Thus, it is important to fully emulsify the neem oil before adding it to the water in your sprayer. If it is not properly emulsified, it won’t mix well. The neem will come out globby and uneven on your plants. I think this is where most people go wrong with neem. Not only does this make the spray less effective, but it increases the risk of damaging the areas of the plants that get heavily dosed with undiluted neem. Strong neem can cause leaves to sunburn. 

Note that even if it is fully emulsified at the time of use, neem oil will try to re-separate from the water with time. If you make a large batch and attempt to store it, ensure to shake it thoroughly and check to see that it is still nicely mixed prior to use! We usually make a fresh batch of spray each time we need it. Especially because we add aloe vera, which should be used immediately after mixing.

Emulsifying Neem Oil 

This is where the soap or silica come in to play. Both act as emulsifying agents, allowing the neem to mix with water. So, should I use silica or soap? That is a personal decision. 

We most often use silica (potassium silicate) to emulsify neem oil, because it provides additional benefits to the plant. For example, silica increases tolerance to stress and drought, and strengthens cell walls – which leads to larger stalks and plants. It also lightly coats the leaves, making them less susceptible to fungal diseases like powdery mildew or impacts of little leaf-sucking insects. 

OR

Liquid soap can also be used to emulsify neem oil. Dilute liquid soap is a common DIY garden spray used against aphids and other soft-bodied insects, disrupting their cell membranes – effectively killing them when sprayed in direct contact. Our choice soap is Dr. Bronner’s Castile Peppermint soap. Insects are repelled by the peppermint odor! Therefore, while soap may not benefit the plant in the same way silica does, it has its own formidable pest-fighting attributes. 

Last but not least, we like to add aloe vera powder to all of our foliar sprays. Again, this is mostly for neem applications to our spoiled cannabis plants. Aloe both feeds the cannabis, and boosts its immune system. However, we do use aloe vera in other ways in our garden, for all types of plants! For example, we create a fresh aloe vera solution to feed seedlings and support freshly transplanted plants. To read more about the benefits of aloe vera and ways to use it in the garden, check out this post!

Mixing Instructions 

1. If you choose to use neem and silica powder regularly, it is easiest to pre-mix a batch of silica powder with water and store as a liquid solution. This makes it ready-to-use and mix with neem whenever you need it. To do so, combine 35 grams of silica powder to 8 ounces of water. Mix thoroughly, and store in a cool dark place for up to a year. This is the small jar of cloudy “water” you see in the images below, which is enough for 48 one-gallon batches of neem oil spray!
   
   
2. Fill your chosen pump sprayer with just under one gallon of water – about a quart shy. Depending on how many and how large of plants you’re working with, scale up or down as needed. You’ll find your groove with time. If you want to use aloe vera powder in this foliar spray, add ⅛ to ¼ teaspoon to your gallon of water now. Cap the sprayer, and shake thoroughly. This is our favorite one-gallon sprayer, and here is a smaller half-gallon option.
   
   
3. Next, it is time to emulsify the neem oil. In small container, such as a half-pint jar or little beaker, combine 1 tablespoon of neem oil with either 1 teaspoon of liquid soap, or 1 teaspoon of the pre-made liquid silica solution described above. Stir thoroughly to combine. This should create a creamy thick yellow liquid. 
   
   
4. Fill a clean quart jar about three-quarters full with warm water. Yes, it is critical to use warm water to aid in mixing, but not hot. Now pour in your neem soap/silica solution. Cap the jar, and shake the living daylights out of it. If it is fully mixed, you won’t see oil droplets forming on the surface. Your neem oil is now emulsified! (It is a tad harder to tell when using soap since it foams.)
   
   
5. Finally, pour the warm quart of neem solution in with the water that is already in your sprayer to create your final diluted mixture. Cap, and shake well to mix.

Essential Oil Additions

Just as the peppermint and neem odors are unappealing and therefore deter pests, essential oils can be used to accomplish the same thing. Essential oils are very, very concentrated – a little goes a long way! If you’d like, try adding just a few drops to the recipe above for a little extra protection. 10-20 drops or so per gallon of water is good.

Peppermint, lavender, orange, tea tree, or eucalyptus are some good examples of essential oils that act as natural insect repellents, though there are many others as well! We personally love this little mix-pack of certified organic EOs, for personal, home, and garden use.

How to Apply Neem Oil Spray

When applying neem oil spray in the garden, I usually wear long, reusable, rubber dish gloves. One, because I don’t want to get all oily – since I usually get deep in the plant and lift dripping leaves as I go. Two, some people can experience a mild dermal reaction or allergy. On the other hand, Aaron doesn’t wear gloves. Take precautions as needed.

We don’t suggest spraying neem on small seedlings, as it may burn them. I would wait until plants are at least a month or two old, and start with slightly less than one tablespoon of neem per gallon. For large mature plants, feel comfortable using the full recipe.

It is best to apply foliar sprays just after the sun goes down, for many reasons. One, beneficial insects are less likely to be present and active then. Second, this gives the spray overnight to do its work and dry a bit. Never apply neem oil in the middle of the day or during sunny conditions. Applying foliar sprays in direct sunlight can cause the wet leaves to sunburn.

Fully drench the target plant until the leaves are dripping. Give your sprayer a shake here and there to keep things mixed. Make sure to spray the undersides of leaves as well. That is where most pests and disease fester!

Frequency

The frequency of application will vary based on your situation, schedule, and the severity of the problem. Neem should not be applied more frequently than once per week, but also doesn’t have a very long-lasting residual effect.

For plants we are actively trying to protect, like our artichokes or cannabis plants (pre-flower only), we spray those weekly or every other week for best results. This same frequency would be good for a plant showing early signs of a pest infestation or disease. On the other hand, our citrus trees are lucky to get a spray once every month or so.

And that is how you properly emulsify, mix, and apply concentrated neem oil.

I hope you found the information in this post useful in your quest for organic pest control. If so, please leave a comment or pass it along to your friends!

May your garden stay healthy, lush, and productive. Remember, an organic garden shouldn’t be free of all insects and pests! That just isn’t natural.

If you enjoyed this article, you may also want to check out:

• Organic Pest Control, Part 1: How to Prevent Pests in the Garden
• Organic Pest Control, Part 2: How to Identify the Top 18 Pests and Beneficial Insects
• Top 23 Plants for Pollinators: Attract Bees, Butterflies, & Hummingbirds!
• Organic Cannabis Pest Control: How to Keep the Bugs Off Your Nugs