Is Neem Oil Safe or Harmful For Organic and Non-Organic Gardens?

Do you ever wish there was a magic, nontoxic, eco-friendly spray that could get rid of those pesky aphids on your broccoli or powdery mildew on your cucumbers? Finding non-toxic garden sprays that are effective and safe can be a challenge. Neem could be your saving grace! 

Almost every organic gardener has heard of the power of neem oil. It’s an organic-approved biopesticide and natural fungicide that comes from a tropical tree.

But is it really safe for organic gardens? What about non-organic gardens? Is it safe to utilize there, or is it harmful? Are the benefits of this miraculous oil just too good to be true? Let’s dig into the origins, uses, benefits, and risks of neem in the garden. 

What is Neem Oil? 

Neem oil is a natural and organic biopesticide sourced from the neem tree (Azadirachta indica).  This large evergreen is native to India, Pakistan, and Bangladesh. It is a member of the mahogany family.  

This plant has been used for thousands of years on the Indian subcontinent as both human and plant medicine. The oil is extracted from the tree’s seeds and made into concentrates for use on organic farms and in organic gardens. 

Ancient herbalists and farmers discovered that no pests ever harmed neem trees because of the stinky sulfur smell. Because of this, they were deemed “wonder trees.” Thousands of medicinal uses have been identified for neem, which is why the Sanskrit name for neem means “to give good health.”  

Neem has been used for hundreds of years in Indian agriculture to also give good health to the land and plants. Only recently has the power of neem been recognized by the western world and it has become integrated into organic Integrated Pest Management (IPM) plans as a vital form of both preventative measures and pest outbreak control. 

How Does it Work?  

The active ingredient in neem is called azadirachtin. It is completely non-toxic to mammals, birds, bees, and plants. In fact, some research has found it could be a potential treatment and preventative for cancer in humans! Ironically, this powerful compound can also be an amazing tool to fight back against annoying pests in your organic garden, without risking the health of you and your family, or the garden ecosystem. 

Neem oil works by repelling insects from treated plants with its stinky smell. It also impacts the insect hormonal systems so it is harder for them to grow, lay eggs, and reproduce. Because of this action, neem is also considered an Insect Growth Regulator (IGR) because it interferes with insect endocrine systems. Some insects are killed by this oil because it prevents them from feeding. 

Neem kills common pests like aphids, whiteflies, mites, leafminers, and pillbugs. It controls bad nematodes when sprayed around the base of plants. It repels slugs from the garden. And it also has fungicidal activities that prevent fungal disease from taking hold and spreading.  

Unlike most pesticides, you don’t have to worry about harming beneficial insects like bees or risking your health to reap the benefits of neem in your garden. 

What Are The Uses?

Neem is found in personal care products from toothpaste to cosmetics, soaps, and shampoos. It has also been used as a medicinal herb in India for centuries; a true testament to its safety for humans!  

In the garden, it also has an abundance of uses:  

• Repel pests 
• Preventative plant health support 
• Kill aphids, thrips, whiteflies, spider mites, Japanese beetles, and more 
• Repels slugs from garden 
• Repels mosquitoes 
• Can act as fungicide against rust, mildew, black spot, anthracnose, blight, and botrytis 

Using Neem in The Garden

Neem comes quite concentrated, so it is always important to follow the dilution instructions before applying to plants. Different brands will have different concentrations, so the ratios will depend on the proportion of oil to water needed.  

If the neem oil is pure, a surfactant (something that makes the oil “stick” to paint leaves) is necessary to add to a homemade diluted neem spray. The soap also helps it thoroughly mix with water. I like to use castile soap like Dr. Bronners.  

To make your own homemade neem spray, simply mix together:  

• 1-2 tsp of natural soap 
• 1 gallon of warm water 
• 1-4 tbsp. of neem oil (depending on concentration and type of infestation)  

Shake to blend. Use a spray bottle to apply to all surfaces, top and bottom, of the affected plants. It is best to apply a neem spray in the morning on a cloudy day and mix only enough to apply it fresh. 

This oil can also be applied as a soil drench to target root-feeding nematodes or and get uptaken by the plant. Use the directions on your specific neem solution to determine what concentrate to apply a soil drench.  

Benefits

Some of the benefits of neem include: 

• Non-toxic to humans, mammals, birds, bees, and plants 
• Comes from a natural source (the neem tree) 
• Kills or repels pest insects (like aphids, thrips, and whiteflies) 
• Interferes with pest reproduction  
• Repels slugs 
• Repels mosquitos  
• Stops the spread of fungal diseases and pathogens (like rust, mildew, and blight) 
• Control lawn grubs and Japanese beetles  
• Pests don’t become resistant (as they do with regular pesticides) 
• Will not harm earthworms, butterflies, or other beneficial insects 
• 100% biodegradable  
• Easy to apply 

Risks of Use

The only way neem could be harmful to an organic garden is if it is applied in large amounts while undiluted. The concentrate is very strong and could burn plant surfaces if applied raw.  

Neem should also be handled carefully like any biopesticide. Though it is organic, it is still a concentrated compound that could hurt your skin as well. I always wear gloves when handling. It is best to keep this oil away from children, as it could be harmful if ingested in very large quantities.  

As with all organic garden sprays, always exercise caution and only use it in moderation. Neem oil has a half-life of 3-22 days in the soil and only 45 minutes to 4 days in water. Wait a week after neem applications to harvest vegetables and thoroughly wash them before eating.  

Can it Harm Plants? 

Some plants are more sensitive than others, so it is best to test your diluted neem spray on only a small portion of leaves first. A few garden crops may be killed by too strong of a neem application. But most plants will tolerate it, unlike Epsom salt, which is often mistakenly used as a “safe” alternative fertilizer by new gardeners.  

Neem oil can also harm garden plants if applied in direct sunlight or extreme temperatures. This may result in “burnt” or yellow leaves. Try to apply on cloudy days or in the mornings or evenings for the safest results.  

Overall, neem is an excellent form of pest and disease control in the garden when things get out of hand. Ideally, it is only used occasionally and preventative measures are taken to keep any outbreaks at bay.