The Knowledge
Uploaded:September 2012

Neem Oil - Hydroponics

Organic Pest Control

by Bill Sutherland

How Neem oil can prevent pest problems in hydroponics

The Neem tree (Azadirachta indica) is affectionately known as 'the village pharmacy' in its homeland of India.


Also known as Indian Lilac, it has as many names as there are dialects stretching from Nigeria in West Africa to Thailand in Southeast Asia. Muarubaini is one such name, which means ‘the tree of the forty’ in Swahili; so named because it is said to treat forty different diseases.

Ancient Ayurvedic texts indicate that Neem has been used for centuries to treat ailments as various as Leprosy, Malaria, Tuberculosis and even good old Acne. Western science has taken an embarrassingly long time to catch up with the local ‘witch-doctors’, but thankfully for us Neem products are now widely used and internationally recognised for their many beneficial qualities; and there are a lot of them.

Noted for its reliance in periods of drought, the Neem tree grows quickly and to heights of fifteen to twenty metres, bearing small white fragrant flowers. Neem oil is pressed from the seeds and fruit of this glorious, fast growing evergreen. Neem oil has so many applications that you could write a whole book about it. In fact a number of people have (see your local stockist for details). For the purposes of this article, we’ll have a look at some of the qualities which underpin Neem oil’s success and at its application in the wonderful world of Horticulture.

The fatty acids which constitute the composition of Neem oil are at the heart of its success.

  • Omega-3, Omega-6 and Omega-9 help to regulate blood pressure, reduce the risk of cardiovascular diseases and help the body fight Cancer and degenerative diseases like Alzheimer’s.
  • Palmitic acid is thought to help regulate insulin levels and is used in the treatment of Schizophrenia.
  • Stearic acid is used in all sorts of things from soap to playing cards and even fireworks.
  • Palmitoleic acid may help to fight obesity, and is possibly partially responsible for body odour (well, seven out of eight isn’t bad).

For the Gardeners amongst us, Neem oil’s most attractive application is as a biopesticide. Where Neem oil differs from most conventional pesticides is that it acts on an insect’s hormonal system as opposed to its nervous or digestive system. The most notable advantage to this is that it doesn’t lead to the development of resistance in the future.

As an insect larva munches its way through your crop, it grows. As it gains mass it becomes necessary for the lava to shed its skin, whereupon the process starts anew. This process of moulting, called Ecdysis, is governed by the enzyme Ecdysone. Azadirachtin in Neem oil acts to suppress Ecdysone, the result being an inability in the larva to shed its skin and accordingly an inability to grow. Ultimately this leads to the larva’s death. Those larvae who manage to escape these effects, usually as a result of too low a concentration of Azadirachtin in the dose, die in the pulpal stage. Those larvae that experience an even lower dose of Azadirachtin emerge as malformed adults who are completely sterile and unable to reproduce. That’ll teach them. Neem oil also acts as an Oviposition deterrent, which means it prevents females from laying eggs.

Neem Oil’s most endearing quality to Gardeners is as a feeding deterrent. When an insect feeds on a leaf treated with Neem oil, Azadirachtin, Salanin and Melandriol in the treated leaf produce an anti-peristaltic wave in the alimentary canal of the insect; inducing the greedy little blighter to vomit. As if yacking its guts up wasn’t enough, its ability to swallow is also blocked. It won’t be going back for seconds any time soon.

Thus, by inhibiting the insects’ ability to eat, grow, mate and lay eggs, Neem oil breaks the cycle of propagation in the community of unwelcome guests, foolhardy enough to squat on your crop. It is claimed that even the slightest hint of the presence of Neem oil on your crop is enough to deter leaf eating insects; and who could blame them for that?

As an added bonus, Neem oil’s efficacy in such small doses means its use is notably benign to helpful insects further up the food chain, like spiders, bees and butterflies that help to germinate crops. Since Humans consume Neem oil in much greater quantities it is obviously equally safe for those of us at the top of the food chain and our lesser mammalian compatriots.

Most insecticides are a bugger to keep in play; they wash out in the rain, burn out in the sun or find some other equally weak excuse to shy away from the job at hand. You can waste time and money on constant reapplication, or you can apply heinous concoction which you’ll likely never get rid of. Either way, the resultant chemical build up is going to send your crop’s toxicity levels through the roof and if you’re particularly unlucky, your own to boot.

Neem oil is, unfortunately, no exception to the vagaries of an all too swift retreat. It is also worth noting that Neem oil is particularly susceptible to UV light. But like the boundless love of a faithful Labrador, where Neem goes, it takes its Goodness with it. Neem oil acts as a systemic insecticide; so rather than washing away into irrelevance, it can be absorbed by the roots of your crop. Taken up into the tissue of the plant it will continue its fine work from the inside. This has the added bonus of deterring larger pests from taking more than a single hearty bite out of your beloved crop.

Not only is Neem oil in possession of insecticidal and nematicidal properties, it is equally a very effective agent in the control of plant diseases, and possesses antifungal propensities. Here again it works in both a preventative capacity and as a treatment. As if that wasn’t enough, Neem oil also contains a number of plant nutrients, meaning it can also act as a fertiliser (see list of nutrients).

So what’s not to like? This glorious substance is effective in both treatment and prevention, bears benefits where experience would suggest side-effects should be, is effective in small quantities and best of all has the environmental conscience of a Trustifarian living in a tree. Perhaps the most prominent cautionary note is that Neem oil is traditionally used as a contraceptive, so it is best not handled by pregnant women and children. Then again, I would no more advice pregnant women or children to handle any pesticides than I would take responsibility for any children born accidentally as a result of using Neem oil as a contraceptive. Keep it safe out there people, and remember to enjoy yourselves.


  • Neem oil is a vegetable oil, so it requires mixing with suitable emulsifiers in order to be soluble in water, which is of course necessary for application. It is advisable to use an organic emulsifier, such as an eco-friendly detergent.
  • 50ml of Neem oil will stretch to 10ltr of sprayable Neem (with the addition of 10-15ml of emulsifier).
  • Spraying should be done within 8 hours of mixing.
  • Spraying is best done in the morning or in the late evening, 5 times at intervals of a week to 10 days.
  • 250-300ml of Neem oil will stretch to 10l of drenchable Neem (with the addition of 20-30ml of emulsifier).
  • Remember: A little Neem oil goes a long way.
  • Neem oil should only be sprayed on plants that have five weeks left before harvest.

Neem Oil Nutritional Value for Plants:

Total Nitrogen - 1.20% by mass
Phosphorus As P - 0.07% by mass
Potassium As K - 0.01% by mass
Magnesium as MG - 0.03% by mass
Copper as CU - 10PPM
Magnesium as MN - 0.40PPM
Zinc as ZN - 20.00PPM
Iron content - 14.00PPM
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