How to Use Neem Oil in the Grow Room

Neem Oil And Cannabis Plants

Luke Sholl
Luke Sholl

Neem oil is made from the seeds of the Azadirachta indica tree that is native to South Asia. The active insecticidal component in Neem is azadirachtin. What makes Neem so special is that it is 100% natural and safe to use. It is non-toxic to humans and animals. There are no negative effects on your plants with Neem oil if you use it properly!

Neem oil is highly effective against many of the most common cannabis pests. It works especially well against soft-bodied insects like spider mites, aphids and white flies. It is also fungicidal and effective against fungi, mould and mildew. Understanding how Neem works is important so that we can maximize its beneficial effect.


How Neem Oil Works

Unlike some chemical insecticides, Neem oil doesn’t work on contact. It doesn’t kill pests right away when you apply it, say if you spray your plants with Neem oil solution. Instead, Neem makes insects stop feeding and interferes with their ability to grow and to lay eggs. To apply Neem effectively we need to be aware of this. There is also evidence that Neem can work as a systemic and that it strengthens plants’ natural resistances and defenses.

The usual way to go about applying Neem oil to plants is to use it diluted as a foliar spray. What is noteworthy to mention is that when you buy a Neem oil product, it is often that the instructions tell you to dilute it in water only. Commonly percentages with some Neem products are 0.1% or 0.2%, eg. 1-2ml Neem oil per each 1 liter of water. This however is less than optimal if not outright wrong!

If you have a basic knowledge of chemistry, you know that oils don’t dissolve in water. To spray Neem oil on your plants, the oil needs to be broken up so it mixes with water and forms an emulsion. Interestingly, many commercial vendors of Neem oil insecticides make no mention of this.

Some growers recommend adding a few drops of liquid soap to your water before you mix in the recommended Neem oil amount. This may work, we however strongly suggest that you look into special insecticidal soap (“potassium soap”) to make your Neem and water solution. With insecticidal soap, you can be sure that it doesn’t contain any potentially harmful ingredients for your plants.

Insecticidal soap doesn’t just help dissolve your Neem oil in water for spraying. It has the big benefit that it alone is a 100% natural insecticide that kills many pests on contact, unlike Neem, which is slower acting. Some commercially available products against aphids are in-fact nothing else than a 2% insecticidal soap solution. In other words, when you combine the Neem oil with soap, you get the best of both worlds. You are killing some pests right away together with the preventative and repelling long-term action of Neem. In addition to that, insecticidal (potassium) soap disintegrates into potash, which is a natural fertilizer.

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Some growers will tell you that using natural, cold-pressed neem oil works better than commercial Neem oil products. There are reasons why we do not recommend that you use cold-pressed Neem oil for the purpose of combating pests.

Cold pressed Neem oil, although “all natural” is usually sold for different purposes such as for soap making in cosmetics and beauty. The packaging of those oils may not mention the right percentage to use for combating pests. In other words: You don’t know how much you will need and risk harming your plants.

We recommend that you use Neem oils that are sold as insecticides instead. Commonly, those are extracts made from Neem oil, containing the active compound, Azadirachtin. Any of those products is normally specifying the exact recommended percentage for insecticidal use. This way you can’t make a mistake with applying too much or not enough.


How To Use Neem Oil

The normal and best way to go about using Neem oil in your grow room is to use it as a foliar spray. With some warm water, make a soapy solution with insecticidal soap, usually 2%. (Alternatively, add some drops of liquid soap that doesn’t contain any perfumes or other ingredients to your water).

  1. Carefully read the instructions on your Neem oil product about the correct percentage to use. With many Neem oil products, the amount you need is very small such as 0.1%-0.2%. However, this can differ depending on product, so make sure you read the label. (Do not simply take a “recommended” percentage you find on some forum on the internet. Some posts mention grossly too high percentages, a sure way to damage your plants!)

  2. With a dropper, mix the right amount of Neem oil into your soapy water.

  3. Fill your soapy Neem solution into a garden sprayer.

  4. Liberally spray your plant from all sides, the upper sides and especially the undersides of leaves. Spray right before the “dripping point” but make sure the entire plant is well covered. When you spray, shake your bottle frequently to keep the solution well-mixed.

Apply this treatment regularly. Due to the hatching cycles of some insects, repeat the Neem oil treatment after 3-4 days. Repeat spraying your plants for about two weeks, until your infestation is under control.


Tips For Applying Neem Oil

  • Foliar spray your entire plants from all sides and try not to miss any spots.

  • Spray either in the evening or early in the morning at low light. Neem degrades in the sun, and lower light helps avoid that your plants may “burn” from spraying.

  • If you spray indoors - and this is possible - move your lights and other equipment up or away for the time when you spray. This avoids splatters that can cause spots or even damage to your equipment.

  • Turn off fans for an hour or two to allow the Neem to soak into the plants without drying too fast.

  • Get a garden pressure sprayer, it will make a big difference. Spraying will be much easier as compared to using a small hand sprayer.

  • Neem oil is non-toxic and so is soap, but you should avoid spraying the buds of plants that are in flowering. Otherwise, this can affect the taste of your harvest.


Neem oil is effective, natural and very safe to use. If you know how to use Neem oil right to prevent and to get rid of most of the common cannabis pests, there is no reason that you ever need to use any harmful chemicals or overpriced commercial insecticides.