What is Horticultural Oil?

Horticultural oil, also known as dormant oil or summer oil, is a type of oil that is used in gardening and horticulture to control pests and diseases on plants. It is derived from petroleum and is highly refined to remove impurities and toxins. Horticultural oil is commonly used as a non-toxic alternative to chemical pesticides, as it is considered safe for humans, animals, and the environment.

How Does Horticultural Oil Work?

Horticultural oil works by suffocating pests and disrupting their life cycles. When applied to plants, the oil forms a thin film on the surface of leaves, stems, and other plant parts. This film acts as a physical barrier, preventing pests from feeding and laying eggs. Additionally, the oil can penetrate the bodies of soft-bodied insects, such as aphids and mites, causing them to dehydrate and die. Horticultural oil also has the ability to smother overwintering pests and their eggs, effectively reducing their populations in the following growing season.

Benefits of Using Horticultural Oil

There are several benefits to using horticultural oil in gardening and horticulture:

1. Effective Pest Control: Horticultural oil is highly effective in controlling a wide range of pests, including aphids, mites, scales, mealybugs, and whiteflies. It can also help control certain diseases, such as powdery mildew and rust.

2. Non-Toxic: Unlike chemical pesticides, horticultural oil is non-toxic to humans, animals, and beneficial insects, such as bees and ladybugs. This makes it a safer option for use in gardens and landscapes.

3. Environmentally Friendly: Horticultural oil is considered environmentally friendly because it breaks down quickly in the environment and does not persist in the soil or water. It also has a low impact on non-target organisms.

4. Versatile: Horticultural oil can be used on a wide variety of plants, including ornamentals, fruits, vegetables, and trees. It can be applied throughout the year, including during the dormant season and during the growing season.

How to Use Horticultural Oil

When using horticultural oil, it is important to follow the instructions on the product label. Here are some general guidelines for using horticultural oil:

1. Timing: Apply horticultural oil when the target pests are in their vulnerable stages, such as during the dormant season or when the pests are actively feeding.

2. Dilution: Most horticultural oils need to be diluted with water before application. Follow the recommended dilution ratio on the product label.

3. Application: Apply the oil evenly to all parts of the plant, including the undersides of leaves and the stems. Use a sprayer or a brush to ensure thorough coverage.

4. Weather Conditions: Avoid applying horticultural oil during extreme temperatures, such as when the temperature exceeds 90°F or drops below freezing. Also, avoid applying the oil when rain is expected within 24 hours, as it may wash off.

5. Repeat Applications: Depending on the severity of the pest infestation, multiple applications of horticultural oil may be necessary. Follow the recommended interval between applications on the product label.

Precautions and Considerations

While horticultural oil is generally safe to use, there are some precautions and considerations to keep in mind:

1. Sensitivity: Some plants, particularly those with waxy or hairy leaves, may be sensitive to horticultural oil. Before applying the oil to a large area, test it on a small, inconspicuous part of the plant and wait for a few days to see if any adverse effects occur.

2. Timing: Avoid applying horticultural oil during periods of active growth or when plants are under stress, as it may cause damage.

3. Storage: Store horticultural oil in a cool, dry place, away from direct sunlight and extreme temperatures. Follow the manufacturer’s instructions for proper storage and disposal.

4. Protective Clothing: When applying horticultural oil, wear protective clothing, such as gloves, goggles, and a long-sleeved shirt, to prevent skin and eye irritation.

5. Beneficial Insects: While horticultural oil is generally safe for beneficial insects, it is still important to avoid spraying them directly. To protect bees and other pollinators, avoid applying the oil when plants are in bloom.


Horticultural oil is a powerful tool in the gardener’s arsenal for controlling pests and diseases. Its non-toxic nature, effectiveness, and versatility make it a popular choice among gardeners and horticulturists. By following the proper application techniques and precautions, horticultural oil can help maintain healthy and thriving plants without harming the environment.