Neem oil toxicity is a rare but possible consequence of using this ingredient in plant care. It is obtained from the seeds of the Azadirachta indica plant and is a bit unstable. It might become toxic to plants if not stored correctly, used too much, or too frequently.Neem Oil

In this article, we will cover all the toxicity aspects related to this multi-purpose oil, so continue reading.

Does Neem Oil Toxicity Occur in Plants?

Yes neem oil toxicity does occur in plants when the oil is expired, and rancid oil is used. Using it less frequently without diluting it with adequate water might also cause plant toxicity. In addition, when the oil is improperly stored, it is used.

Toxicity develops in expired neem oil due to the breakdown of azadirachtin and other constituent compounds. Larger fat molecules also break down and produce rancidity in this oil over time. This breakdown of neem oil is a natural process expedited by air, water, and light, and when you place this, precise oil on the plants, the result will not be a positive one.

– When Expired Oil Is Used

Using expired oil cold pressed from the seeds of the Azadirachta indica plant might cause toxicity in plants. The older the oil is and the more it is used, the more severe the symptoms will be.

Using a small amount of expired oil is not a problem, but using too much of it should be avoided at all costs. The reason is that even after a while, this organic oil is prone to be expired, and you would also know this when you open it, and it doesn’t have the fresh and earthy smell anymore, but it is more intense and heavy.

The thing about expired oil is that it has lost all its valuable properties. It will not eliminate bugs and fungal infections attacking your precious plants. It does develop harmful breakdown products that enter the plant cells and cause damage on a cellular level because it is more dangerous than helpful now.

This oil comprises over 140 different types of molecules as part of its composition. Some of these compounds are more well-researched than others because of their significance. Three include azadirachtin, Nimbin, and Nimbin, which contribute to the oil’s antifungal and pesticide effects.

Unfortunately, the compounds that form the neem extract and oil are not very stable in nature. They break down into more minor compounds, some of which are harmless while others are potentially toxic. The larger fat molecules break down into smaller ones during this expiry process which causes the oil to become rancid.

Neem oil expiry is a natural process that starts occurring even within a sealed, airtight bottle. Light, air, and moisture exposure will only speed up this process. Rancid oil becomes more toxic when it becomes contaminated with dust particles, dirt, or metals.

– When Concentrated Oil Is Used

A neem oil spray must be diluted a lot before it can be used safely on plants and vegetables. By a lot, we mean one gallon of water dilution for just one tablespoon of oil. Using too much oil for faster results will cause toxicity instead of the expected neem oil benefits.Benefits of Using Neem Oil

As long as the oil remains sealed in a bottle away from light and extreme temperatures, its compounds like nimidin and azadirachtin remain stable for a long time. Sealed oil appropriately stored can last about two to three years. Factors that might increase or decrease the shelf life of a sealed oil are packaging, storage conditions, and purity of the extracted oil.

Despite being stored properly, the oil will last up to three years because its compounds eventually disintegrate. Make sure that you purchase oil from a reputable seller to get an authentic product that lasts for a long time under the right conditions.

Once the oil bottle is opened and exposed to outside air, humidity, light, and temperature changes, these compounds slowly start disintegrating. The rate at which they break down depends on several factors, like exposure to sunlight and the amount of humidity in the air. Once opened, you must use the oil within six to 12 months and then remove it.

– When Improperly Stored Oil Is Used

It turns toxic if the oil is not stored correctly and gets contaminated with dirt or metal particles. Oil in a bright place gets exposed to light and breaks into poisonous products.

This oil must be stored in a dark, cool, dry, and clean spot in the house and used within six months of opening its bottle. When you haven’t stored it in an airtight container, and it has been contaminated, the oil will be prone to be weaker and cause harm to the plant.

Neem oil expiry date decreases drastically when mixed with water. Once the oil is taken out of its bottle and mixed with water, it is best to use it within eight to 12 hours. You can store a water plus oil solution for about 24 hours in a cool, dry place away from a light source of any kind.

For mixing oil, use pure and filtered water so that the resultant mixture will last a long time. Oil mixed with distilled water, reverse osmosis water, and filtered water forms a much more potent pest control mixture that lasts for about a day. Tap water is ideally not recommended because it contains chemicals that react with the oil and decrease its shelf life to about eight hours or less.

What Are the Side Effects of Neem Oil Toxicity in Plants?

The side effects of neem oil toxicity in plants include burning leaves, killing pollinators, and growth retardation. The sprayed plant becomes greasy and attracts dust and dirt. Toxic quantities of oil either kill the seeds or stop them from germinating.

– It Causes Foliage Burning

Too much oil causes toxicity, leading to chemical burns in the affected plant. This usually happens when a concentrated spray of the oil is used carelessly. The oil particles heat up rapidly and cause burns to the leaves and stem sheaths, and you will see it weaken and look dull.Causes of Foliage Burning

Plants that are grown outdoors suffer the most from this kind of toxicity. In this case, you should remember that the plant will start to change its features, and so it will weaken, and at times as such, you may tend to apply it more because you don’t see the correct result. Which is why you can also place it intensely and the result would be to see leaves getting a different color and developing a burn.

Even a diluted mixture of oil and water might cause foliage burns if the surrounding temperatures are too high or the sunlight is too bright. For this, a single tablespoon of oil needs an entire gallon of water to make it safe.

This oil is also used as soil soaks in which the roots are watered with an oil and water mixture. Again, a concentrated blend will cause the roots to develop toxicity and suffer from burns.

– It Kills Pollinators and Other Important Insects

This oil, used in toxic quantities, will affect plants by killing pollinators and other beneficial insects. An adequately diluted mixture of oil and water does not harm bees, earthworms, and butterflies. The killing of pollinators is terrible for plants because their fertilization, flowering, and fruit-making processes are impacted.

The toxicity of the neem leaf oil on the plant’s soil will kill earthworms present in the soil. Remember that earthworms are super crucial for maintaining the soil’s aeration and drainage.

They help break down organic matter into smaller pieces easily absorbed by the roots. If the earthworm population of the soil is disturbed, the plant suffers more, because, naturally they are there to help the roots and the soil to stay adequately nourished.

On the contrary, when it comes to the concern of is neem oil safe for bees and butterflies, you should know that yes, it is, only if it is not sprayed directly on them. They will not be harmed if they land on a plant recently sprayed with this oil spray, unless it is not diluted proerly. This makes it one of the safest pesticides because it does not harm pollinators.

– It Makes the Plants Greasy

It is only natural for oil to leave a greasy residue on the surface of the plants. Even when we dilute a single tablespoon of oil in one gallon of water, this mixture makes the plant oily. You can see and feel the oil on the plant for at least two to four days after a spray, and if the cells are blocked it will hinder the growth.Greasy Indoor Plants

Having a layer of grease on the plant attracts insects, to it, and this due to how ot also traps mold and dust and turns the plant dirty. If the oil falls on the growing buds of flowers, the taste of the resultant fruit might be altered forever. Too much oil might cause toxicity that prevents these buds from flowering altogether.

Neem oil is made from cold pressing the seeds of the neem tree plant. This oil is deep yellow, golden, to olive green in color and smells pungently like roasted almonds, and that is what is neem oil is made from. After being cold pressed, it remains stable in a sealed bottle for up to three years before expiration.

– It Can Kill Stressed Plants

Plants already under some stress cannot survive the toxicity of neem oil. Their leaves quickly turn yellow or brown and then fall off. Once more than one-third of a plant’s foliage is gone, it is as good as dead.

This toxicity occurs more often when this oil is poured over the roots as a systemic pesticide. Examples of stressed plants are those that have recently been transferred from one pot to another. Plants that are currently flowering are also under reproductive stresses and succumb to toxicity.Growing Seeds in Soil

Just as it can kill stressed plants, this oil is unsafe for humans to eat and should be used topically only. It is not digested well by our bodies and will cause digestive issues in the best-case scenarios when you think is neem oil safe for humans to eat. In the worst-case scenario, consuming a significant quantity of this oil might lead to toxicity and poisoning.

– The Toxicity May Kill Seeds

Seeds are susceptible and will not germinate unless the conditions are 100 percent favorable. Unlike grown plants, they cannot tolerate being sprayed with neem and other home remedies. Several studies have shown that seeds scattered with even properly diluted oil solutions fail to germinate.

Even if some of the seeds with toxicity do germinate, they often do not grow into healthy plants. The resulting plant will have stunted growth and developmental problems.

Moreover, seeds are often grown under high temperatures and humidity and exposed to bright sunshine. What happens around the seeds is that the neem oil gets heated under such conditions and roasts the seeds instead of helping them germinate.

– It Hinders the Growth

When the effect of this oil’s toxicity during the seedling stage is severe growth retardation in the plant, the same might happen after toxicity is produced by a soil drench made of toxic oil. The plant will have fewer leaves that will be smaller and might even be disfigured.

The plant’s natural resistance against bugs and insects is significantly impacted. During the flowering stage, such a plant will produce fewer flowers and then fruits. The quality and taste of the fruit are at a lower rate than experienced in previous seasons.

In short, if you are also considering, is neem oil safe for vegetables, you should know that yes, it is, just as it is applied in the correct quantity at the right time. Stop spraying it for at least three weeks before harvesting the vegetables. Do not use a concentrated spray or spray on flower buds during the flowering stage of the plant.


Although it is generally safe, toxicity from the Azadirachta indica plant oil is always possible.

  • Neem leaf or seed oil is not toxic when appropriately stored and used correctly as a plant pesticide and fungicide.
  • It will become toxic when exposed to air, moisture, and light and then used on plants in large amounts.
  • Instead of removing bugs like other botanical insecticides, neem oil side effects will develop, such as leaf dropping and yellowing.

After going through this guide, you are better equipped to prevent potential toxicity in your plants from using this oil.

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