Neem oil has risen in popularity among plant lovers, mainly because of its effect on plants' leaves- it makes them 'shiny'. Unfortunately, many plant enthusiasts buy this product without really understanding what it can really do to our plants. 

As gardeners, we don't want to waste our money on gardening  products that don't give enough protection to our plants the way they should. Choosing a good quality neem oil product is therefore important.   While neem oil has been proven effective in controlling at least 200 kinds of pests that harm our precious plants, this is only true if you use a good quality neem oil. Cheaper "neem oil" variants have become available in the market today but they do not deliver the best results expected from the product. Thus, we only end up being disappointed, and worst of all, our beloved plants suffer from our wrong decision.   

Neem Oil and its Benefits in Gardening

As an advocate of sustainable gardening, I prefer non-chemical solutions in managing pests. In many instances, using synthetic chemicals to control pests often create harmful effects on our environment and even expose our own family to health risks. However, finding a good balance between efficacy and its environmental impact can be a difficult choice.

Fortunately, neem oil is the only bio-pesticide that is not only proven effective in controlling more than 200 kinds of garden pests, but is also environment-friendly. Neem oil kills insects at all stages of its development - from egg, larvae to adulthood, including the most common pest problems like aphids, spider mites, scale, leaf hoppers, white flies, mealybugs, caterpillars, thrips, slugs, flea beatles and the like. 

It is important to note that neem oil does not  kill insects upon contact.  What it does is to work internally within the bug's biological system by causing it to stop feeding and lose fertility, until it dies eventually. The pest needs to be exposed to neem oil by ingesting a portion of the plant that has been sprayed with a neem solution. This is why it is not harmful to bees, earthworms and other beneficial insects that do not feed on plants. 

Neem oil is also effective on the insect's larvae by eradicating them before they start wreaking havoc on your plants. Likewise, it is proven effective on harmful soil-bound nematodes that often destroy the plant's root system.  In addition, it has some anti-fungal properties that prevent common fungal diseases like mildews, black spot, scab, rust, leaf spot, anthrachnose and tip blight.

Neem oil is bio-degradable and it does not accumulate in the soil or plants regardless of the number of times you use it.  It is generally safe to use around humans and pets. Studies have shown that ingesting plant leaves that have been sprayed with neem oil does not cause any permanent harm on mammals.  Neem has been used as bio-pesticide in India for more than 100 years, and has been reported as generally safe on humans and animals.

Why choose Pure Cold-Pressed Neem Oil

What makes neem oil most effective as a bio-pesticide is this natural compound called "Azadirachtin" that is found mostly in the neem seeds. When buying Neem Oil,  look for the "Pure Cold-pressed Neem Oil" variant.  In a cold-pressed extraction process, neem oil is obtained by pressing or crushing the seeds or subjecting it to a certain regulated low temperature in order to extract the oil.  Pure cold-pressed neem oil is the highest quality because it preserves most of the beneficial compounds that are mostly found in neem seeds, particularly "azadirachtin".    

Many of the cheaper neem oil bottles sold in the market use neem leaves to extract the oil, instead of the neem seeds. While neem leaves may contain some level of azadirachtin, it is the seed kernels that contain most of this substance. When extracted from the seeds, the neem oil produced has a stronger and more pungent scent that the neem oil extracted from leaves or bark.

These cheaper variants use heat (usually by heating them in a carrier oil - like coconut oil or vegetable oil) to extract the neem juice.  In other words, while they claim that they are selling "pure neem oil",  neem oil produced through this process is not really pure and is already highly diluted (20% neem and 80% carrier oil). This makes their effect on plants oftentimes questionable.

So how do you know if you are buying the right stuff?   Pure cold-pressed neem oil emits a strong nutty/ garlic aroma.  Many would find its smell unpleasant, but this is what works wonders for your plants, and it also serves as a repellant against many insects. The other neem oil variants have a milder aroma because they have already been diluted or mixed with vegetable oil. You know if you are buying pure, unadulterated neem oil when the smell is strong (but tolerable).  

How to Use Neem Oil

If you are using pure cold-pressed neem oil, you only need a small amount for every use.  It's actually more economical. Simply mix 1  teaspoons (5 ml) per liter of unchlorinated water. Since oil doesn't mix well with water, you need a surfactant in order to blend it thoroughly. For this, use 1 teaspoon of any mild organic liquid soap, or if this is not available, use a few drops of dishwashing liquid.  I  usually recommend castile soap because it has natural insecticidal and anti-bacterial properties that complements the powerful effects of neem oil. If the pest infestation is heavy, you can increase the neem dosage up to 2 teaspoons for every liter of water.  

Mix all of these ingredients in a spray bottle and then shake well until oil and water no longer separate. Use this solution to spray generously on plant leaves, stem and roots at dawn or late in the afternoon. If the infestation is heavy, repeat application after 2- 3 days. Once the pests are controlled, a regular weekly application is recommended as a preventive measure. 

Why you shouldn't buy "Ready-to-Use Neem Oil Spray"

Also in recent months, there has been a proliferation of sellers marketing their Ready-to-Use Neem Oil Spray  online. They package their products in very nice bottles and infuse different fragrant aromatic scents. Some would even call  them as "Pure Neem Oil Spray".  A naive gardener is easily fooled because he thinks he is getting good value for money. 

It is important to note that neem oil is bio-degradable once it is mixed with water. After mixing it in water, it starts to break down within 45 minutes and and its efficacy diminishes over the next 48 hours.  This is why I strongly advise against storing or using any mixed solution that has been left in the spray bottle for more than 3 days.

The active neem oil components (if any) in these "Ready-to-Use Neem Oil Spray" products have already disintegrated and are no longer effective, by the time this product reaches you. To put it bluntly, you are completely wasting your money if you buy these ready-to-use neem spray products. Without the active ingredients in neem oil, what remains in the solution is the neem fatty acid which has minimal beneficial effect on plants, except perhaps to make them a little shiny. This is no different from using any vegetable oil.   

Some Important Reminders

While neem oil is generally safe around humans and pets, it is more prudent to keep it away from small children, as in any substance that you would use in the garden.  Ingesting large amounts of  this substance may cause various adverse effects or reactions. Likewise, always consult a physician before applying neem on your skin or hair. If you suspect that you are pregnant, it is safe practice to take necessary precautions like using gloves or a face mask when using neem. For pets, ingesting neem may cause trembling and other side effects in cats and dogs, which are usually not fatal.  Consult your veterinarian before using neem oil on pets.

References:  

"Using Neem Oil " by Shannon McKee,   www.davesgarden.com

"Neem Oil Facts (Definitive Safety Guide)"    www.peststrategies.com 

"Azadirachtin vs. Clarified Hydrophobic Extract of Neem Oil"  www.blog.gardeningknowhow.com

"The Benefits of Neem Oil,"   www.planetnatural.com