Neem oil, often referred to as margosa oil, is a type of vegetable oil that is extracted from the fruits and seeds of the neem tree (Azadirachta indica), which is native to the Indian subcontinent but has since been spread to many other tropical regions.
Neem oil is able to burn plants.
Let’s take a brief look at what damaging bugs perform to plants and how neem oil functions to comprehend why it can burn and harm your plants.
Plants are typically harmed by destructive garden pests in 3 distinct, occasionally overlapping ways:
- They eat the leaves of plants.
- They rip holes in the leaves and absorb plant nutrients.
- Through the interchange of bodily fluids, they spread disease.
Anyone who has ever had a garden knows that some insects, including armyworms, cabbage looper larvae, flea beetles, and hornworms, devour plants while others steal essential nutrients (such as aphids, spider mites, and whiteflies).
Some soft-bodied insects can be killed instantly by neem oil sprays because, when combined with water and liquid soap, they function similarly to oily soap water sprays in that they coat the insects in oily soap, preventing them from breathing.
However, this is not how neem oil typically gets rid of bugs. Neem oil coats plant foliage in a very thin, oily layer that, after drying, is invisible to human eyes, rather than killing insects on contact. As soon as insects start eating or piercing your plants, they unknowingly consume trace amounts of neem oil, which causes azadirachtin to circulate throughout their bodies and kill a variety of insects by causing various types of cellular damage.
Neem oil won’t harm ladybugs, earthworms, or other helpful pollinators because they don’t eat plant leaf, which prevents them from ingesting neem oil.
The problem arises because, if you’re not careful, the same thin, oily film that harms pests may also harm your plants.
Using neem oil sprays carelessly can result in the following:
Neem oil will actually roast your leaves if applied on hot days, especially if it is applied during the hottest hours of the morning and afternoon. This is because the heat from the sun will raise the surface temperature of the oil.
Not only might this result in leaf burn. If you use this method on an extremely hot, bright day, you can even kill a plant by covering it in neem oil.
Applying it on warm days Neem oil still has the potential to burn plant foliage, even when applied in the early morning. Although the burns won’t be as severe as they would be on hotter, sunny days, you will still notice damaged foliage.
On days like this, I don’t think it would be very easy to harm your plant, but it’s preferable not to take a chance!
Neem oil can physically suffocate plants if used excessively since plants breathe by absorbing oxygen from the air through numerous small pores on their leaves known as stomata (more on that below). Neem oil is applied to a plant to temporarily close these holes.
But because neem oil quickly dries up and degrades over a few weeks, any stomata obstructions that occur are just transient and won’t harm your plants.
Nevertheless, depending on the degree of the infestation, if you apply neem oil once every day or two as opposed to once every 4–7 days, your plants will suffer—as well as perhaps your beneficial insects.
Another way to harm or burn your plants is by using too much neem oil in your application.
I always advise combining neem oil concentrate according to the instructions on the box, but generally speaking, I use this formula if I’m using my 1-gallon garden sprayer:
Is neem oil toxic to people?
The neem tree, a swiftly expanding and remarkably resilient plant that is native to Asia, is the source of neem oil. The oil from the tree’s seeds is used for numerous beneficial purposes, including insect control. Neem oil has a low toxicity rating, making it less damaging to beneficial creatures like pollinators than many synthetic pesticides. Additionally, it is not poisonous to people. It’s still advisable to keep your distance from the eyes, though. As some neem oil products have additives that may irritate skin, prevent direct contact with the chemical unless you have carefully read the label and verified it is safe for skin.
Neem oil is widely known as an efficient natural pest control tool, but few gardeners take into account the numerous uses for this oil in the garden, on the lawn, and even within the home. Here are some neem oil uses for the garden, the house, and other areas.
Which plants should not be exposed to neem oil?
I started using neem oil in my garden a few years ago to get rid of spider mites and aphids, and I’ve grown to adore it. I’ve had great success using neem oil, which naturally repels insects, especially when it comes to keeping the pests away from my tomato plants.
But I recently discovered a hard lesson: Neem oil simply isn’t a favorite among all plants. Thus, the issue arises: Which plants should you avoid using neem oil on?
Herbs like basil, caraway, cilantro, dill, marjoram, oregano, parsley, or thyme shouldn’t be sprayed with neem oil. Neem oil should only be sprayed sparingly on plants with fragile or wispy leaves, such as spinach, arugula, lettuce, and peas, to avoid burning the foliage.
Be careful while mixing and applying neem oil, though, as even hardier plants with tougher foliage might be scorched (or even killed) if you don’t.
Neem oil is made to cover a plant’s leaves and any invasive insects lurking among them in an oily film that will suffocate some insects and harm many others by damaging their cells. Neem oil is an oil, though, so even on a moderate day, if you ignore good advise and spray at the wrong times, you risk literally cooking the leaves of your plants.
In light of this, let’s look at a list of plants that tolerate neem oil, those that are sensitive to neem oil, and those that don’t actually require neem oil because they already ward off many of the most pesky bugs.
Is neem oil harmful to the skin?
Neem oil is incredibly strong but safe. If you have sensitive skin or a skin condition like eczema, it could have negative effects on you.
If you’ve never used neem oil before, start by dabbing a small amount of it on a spot of skin far from your face. You may want to further dilute the oil or stop using it altogether if redness or irritation appear.
An allergic reaction could be indicated by hives, a severe rash, or trouble breathing. Neem oil usage should be stopped right away, and if your ailments worsen, you should see a doctor.
Children should not use neem oil due to its strength. Consult your doctor before applying neem oil to a child.
Neem oil should not be used if you are pregnant or nursing because there have been no studies done to determine whether it is safe to do so.
What occurs if neem oil is applied to plants in excess?
Numerous organic chemical components have been found in neem oil, as demonstrated by studies, however azadirachtin is by far its most significant component.
This naturally occurring substance doesn’t kill pests right away, but after ingesting it, it will interfere with their capacity to feed, molt, and breed, ultimately killing them within a week.
Bugs are also covered in a thin coating of oil by neem oil. If you spray adult, hard-bodied bugs with neem oil, such as leaf-footed bugs, squash bugs, and stink bugs, they will get irritated but usually not die. Aphids and spider mites, which have smaller, softer bodies, are more vulnerable to anything that covers them in oil, especially if they are in the nymph stage. The azadirachtin will kill them if the oil itself doesn’t.
Fortunately, the oil won’t harm helpful pollinators, and once it’s diluted, sprayed on plants, and exposed to sunlight and the environment, it will start breaking down swiftly.
Neem oil can be applied more than once every 4–7 days, although generally speaking, you shouldn’t do so to maximize its effectiveness.
In other words, if you apply neem oil every 1, 2, or 3 days, you’re using it excessively and risk causing your plants slow-moving, long-lasting harm.
Neem oil will cover the leaves, branches, and blossoms of your plants in a thin film of oil, which is why it is true.
As I mentioned above, this oily layer will begin to disappear within a few hours, but if you keep reapplying neem oil without timing your applications properly or separating them so that the oil completely degrades in between, you risk seriously harming your plant in two ways.
The most obvious approach to harm your plants with neem oil is in this manner. Neem oil will heat up if it is exposed to direct sunshine before it has had a chance to properly dry, just like the oil in your frying pan does when it is exposed to higher temperatures.
Neem oil will likely harm whatever leaves it comes in contact with once it has heated up, resulting in burns that appear as streaks, splotches, or even spots, as well as eventual leaf rot. If your plant has too much neem oil on it, you risk completely killing it by damaging too much of its foliage.
Neem oil spray applications should always be made in the early evening for the simplest way to prevent these issues. While the light is still bright enough for me to see clearly, I do this as it is setting. As a result, there is no doubt that the neem oil will have at least 10 hours to dry before the sun rises the next day.
I once neglected to apply neem oil in the evening and, against better judgment, chose to do so the following morning. I believed that by doing it early, it would dry before the sun could do any harm, preventing any scorching.
Fortunately, I had only lightly sprayed a few plants with neem oil, so they quickly recovered. However, I learned from the experience not to try to make up for missed neem oil applications the following morning. Simply wait until the suitable time the following day, then spray your plants.
Neem oil treatments frequently can result in unwanted side effects on three critical biological processes that all plants carry out in addition to the potential for foliage burns:
The process through which plants convert carbon dioxide, sunshine, and water into oxygen and carbohydrates is known as photosynthesis. However, the precise mechanism by which this happens is less well understood.
Simply put, stomata (or stoma if you’re referring to a single pore) are epidermal pores found in plants. By absorbing carbon dioxide from the environment, these tiny apertures are crucial to photosynthesis. The cells that surround each stoma serve as gatekeepers. When there is sufficient carbon dioxide in the plant, the cells close the stoma to momentarily slow or stop the flow; when there is insufficient carbon dioxide in the plant, the cells open the stoma to let more CO2 in.
Therefore, stomata are essential for photosynthesis. They don’t participate in the actual chemical reactions occurring inside the plant, but they do manage how much and how frequently carbon dioxide enters the plant, so regulating a crucial aspect of photosynthesis.
To take in carbon dioxide, stomata open, but in the process of doing so, they also lose something: water. Also in plenty. According to the U.S. Geological Survey, a single huge oak tree can transpire up to 40,000 gallons of water annually, compared to up to 4,000 gallons for an acre of maize.
The stomata control when and how much each plant transpires at any one time. Transpiration fluctuates depending on a wide range of conditions, including heat, humidity, wind speeds, and soil moisture, to mention a few.
When plants engage in photosynthesis, they draw carbon dioxide from the atmosphere and combine it with water to produce oxygen and carbohydrates using energy from sunshine. As an unneeded consequence of the photosynthetic process, they then expel the extra oxygen.
It should come as no surprise that these exchanges also happen through the plant’s stomatal openings, especially during the day. As a result, the open stomata serve two purposes: they let CO2 in while also enabling oxygen to escape.
Studies have demonstrated that anything that interferes with these stomatal routes would have a negative effect on plants, obstructing their biological functions and retarding their growth.
And this brings me to my concern with neem oil: if you spray neem oil too much and too often, you run the risk of coating and re-coating your plant’s leaves in oil, which could clog the stomata and impair the plant’s capacity to absorb carbon dioxide and release both water and oxygen.
How long does neem oil take to start working on plants?
Neem oil has two distinct purposes. The first is suffocating or smothering the insects that are eating your plants. Only small insects, like spider mites, do this task well. Due to the compounds in the neem oil, the second purpose is to destroy any insects. Both the tiny and larger insects on your plants are killed by this.
The substance, known as azadirachtin, interferes with the insect’s regular biological processes, causing them to lay dormant and eventually perish. It’s a safe way to get rid of pests on your plants. You are not in any way hurting your plant when you use neem oil. On the other side, you are greatly decreasing the appeal of your plant to insects and other pests.
Remember that Neem Oil takes time to start working. Before you start to get the desired outcomes, it normally takes a few days, usually 3 to 4 days, and a few sessions.
Do you apply neem oil to leaves or the ground?
Neem oil should always be sprayed across the tops and bottoms of leaves when treating a plant for insects, whether as a curative or preventative approach. This is because insects prefer to congregate on the underside of leaves. In case any animals have found their way to the stems or soil, you should also lightly treat those surfaces.
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Neem oil should only be applied to healthy plants. Your vegetation may be battling with water, sunshine, or nutrient imbalance if it is yellowing, browning, droopy, or otherwise seems wrong. Neem oil may exacerbate the issue.
Finally, avoid spraying neem oil on plants that are placed near a window that is lit up. To prevent leaf burn, Halleck advises against using horticultural oils on plants when they are directly exposed to the sun.
Move your plant into a darker area, such as the bathroom, before spraying, and wait two to three days before relocating it to a more sunny location. This should give the neem oil adequate time to degrade.
Neem oil can harm your plants’ leaves if used excessively, so always read the bottle’s directions before using it to spray.