Neem Oil For Plants
As a natural insecticide, fungicide and bactericide, people have been using neem centuries. You can successfully control aphids and mildew, and another plus is that the leaves sprayed will be noticeably healthier.
Does Neem Oil Cause Any Problems?
The great thing about neem seed oil is that it mainly affects plant-feeding insects that suck or chew on leaves, so beneficial insects including bees, butterflies and other pollinators that feed on nectar aren’t much affected.
Other beneficials such as ladybugs, earthworms and spiders aren’t affected either unless they’re sprayed directly with a fairly heavy dose.
Research shows that only repeated applications of very high concentrations of neem – far exceeding those you’ll be using – had a small impact on some bee populations.
It is not recommended to blanket the whole garden with neem oil.
As for human safety, pure neem oil is not only 100% natural and non-toxic to humans and other mammals, but is actually used in many applications for our health – neem oil for skin, neem oil for hair, neem oil for dogs, and so on.
The residue from spraying your vegetables is non-toxic, but when ingested in larger amounts, neem oil can be irritating to eyes, skin and stomach, and negatively impact fertility, so as with most things we spray in our garden, don’t drink it or go splashing it all over your face.
Neem breaks down quickly without a lasting residue and has a low environmental impact. You can spray neem pretty much up to the day of harvest as it breaks down quickly and is non-toxic to humans.
The only thing to be careful of is not to spray too close to waterways because neem oil has been shown to be mildly toxic to aquatic organisms.
Because azadirachtin acts on the hormonal system, insects don’t develop resistance in future generations, thereby making it a sustainable solution.
While azadirachtin is the most researched metabolite, I expect there are many others that are involved.
Neem oil fungicide uses. Organic compounds in the oil spark an immune response to prevent fungal diseases such as mildew, black spot, rust, rot, scab, leaf spot and blights.
And a quality, cold pressed neem oil will occasionally control some of these diseases when they’re already present.
It’s also been used as a seed treatment to successfully prevent phytopathogenic fungal diseases.
In terms of where to buy neem oil, be sure to seek out a product that is a cold pressed, 100% pure neem oil, preferably organic.
Pure neem oil for sale that was cold pressed contains much higher levels of active ingredients, which makes it more effective.
If possible, try to find the percentage of azadirachtin. This particular product varies between 1500-2200ppm. A higher ppm is achievable, but often by way of chemical extraction.
How Much Neem Oil Do You Need?
16 oz. will do about 1000 square feet of orchard for a whole growing season, and several times that size for a vegetable garden.
Store your neem oil in a cool, dark place. Room temperature is okay, or the refrigerator is a good place for it, too. It will last about two years if you do this.
You can use neem oil throughout the growing season on all types of plants. Just be careful with seedlings and young plants in general, as they tend to be more vulnerable to any type of spray.
It’s best to start early in the season to prevent the main infection period of fungi, disrupt egg hatch of soft-bodied insects and target overwintering moths in the trunk and soil.
On plants that you know will have pest problems, you can spray for prevention every 1-2 weeks starting in late winter, and especially when the problem season approaches for that plant, and then for maintenance every 2-4 weeks after that.
If you have a specific pest to control, you can spray every 3 days for at least 2 weeks. This is approximately the length of one life cycle for many insects.
Like unrefined coconut oil, pure neem oil becomes solid and thick at cooler temperatures, so if necessary, you can warm up the whole bottle by placing it in a pot of warm water, or you can just mix the neem directly with warm water before spraying. Don’t use hot water as heat destroys azadirachtin.
The oil and water will separate, so you’ll want to use an emulsifier to stabilize the mixture. Generally what’s used is liquid soap, which also has insecticidal properties. Unfortunately, dish detergents are quite hard on plants, so I use a non-toxic Castile soap such as Dr Bronner’s.
Total application rate of neem oil is 1-2 cups per 1000 square feet per year, which could be divided into small-dose, weekly sprayings or larger-dose, monthly sprayings. For example, if you spray 6 times this year, that’s about 3-6 Tbsp of neem oil per 1000 square feet each time. Lean to the lower end if your plants are small, like vegetables in spring.
mix 1.5 Tbsp of neem oil with 1/2 teaspoon of non-toxic liquid soap per gallon of water and shake like crazy before and during application. This makes for a 1:170 ratio of neem oil to water (1:150 to 1:200 seems to be the norm). That amount will do about 250-500 square feet, but don’t spray too much on young seedlings – it’s better to wait until plants are bigger for most types of foliar spraying, as tiny plants can be quite vulnerable to overapplication.
If you’re using a standalone sprayer and plan to spray, for example, 3 gallons of water, that’s about 4.5 Tbsp of neem oil (1.5*3). For soil and trunk applications in early spring and late fall when there are no leaves on your trees and shrubs, you can double the dilution to 3 Tbsp of neem oil per gallon of water, but let’s stick with 1.5 for this example.
If you’re using a hose-end sprayer, here’s how I do it. First, mix the neem oil in a jar with warm water and soap. Fill a jar with about 7 times (I’ll explain why 7 in a minute) as much warm water as the neem oil (nearly 2 cups of warm water for our 1.5 Tbsp of neem in this example) and add 1/2 teaspoon of non-toxic liquid soap for each 1.5 Tbsp of neem oil (1.5 teaspoons of soap in this example).
Then slowly pour in the neem oil while vigorously mixing the liquid. This is similar to how a good salad dressing is made – the oil needs to be added slowly and mixed really well in order to emulsify it. Alternatively, using a blender to mix this all together can work, but then your blender smells like neem, which isn’t very nice.
The reason I use this seemingly random number of 7 times as much warm water as neem oil with a hose-end sprayer is because if I set that sprayer to spray 10 Tbsp of neem oil per gallon of water, and I’ve already mixed that neem oil with 7 parts water, that brings the actual ratio back down to about 1.5 Tbsp per gallon of water (if that gets used up too fast for you, bring it down to 5 Tbsp per gallon of water).
Even better, use less water and instead add some liquid fish and/or liquid seaweed fertilizer and spray them at the same time. I always try to combine products when possible since I’m out there spraying anyway, and fish and seaweed are the best matches for pure neem oil.
For those of you using my hose end sprayer or another pint-capacity sprayer, I add 4 Tbsp of neem oil to the sprayer along with 1/2 Tbsp of non-toxic liquid soap, and then fill it up the rest of the way with warm water (and perhaps 1/2 cup of fish or seaweed). Shake very well. Set to setting 10 and spray.
Another way to do the math is to make a 25% ratio of neem oil to water (1 Tbsp of neem oil for every 3 Tbsp of water). Then set the sprayer to setting 5, which is a 2% ratio (5 Tbsp per gallon of water). That 25% ratio with that 2% ratio gives a 0.5% ratio (1:200).
Use your neem and water mixture within 8 hours because it will break down afterward. Then clean your sprayer immediately to keep it from clogging up with oil.
When you spray the leaves, make sure that you also spray the undersides because insects like to hide there.
It’s always useful to spray the soil too because insects lay their eggs in the ground, and because the fatty acids in the oil are beneficial for the soil food web.
Don’t be discouraged if you don’t see immediate effects. Remember that neem oil concentrate primarily works not by contact, but by disturbing the hormonal systems of insects, so it can take some time.
For educational purposes only