At a glance
- Product choice
- Plant and pest must both be on the label
- Small-area test
- Spray a few leaves and watch them for 1 to 2 days
- Temperature range
- About 50 to 85°F for oil sprays
- Coverage target
- Leaf undersides, stems and the joints where leaves meet stems
- Poor match
- Fungus gnats and adult whiteflies
The sections below match neem oil to the pest, show which houseplants it can hurt, and walk through spraying, repeating and dealing with leaf burn.
Is neem oil the right tool for the pest on your plant?
Products sold as neem fall into two groups that work differently. Ready-to-use sprays contain clarified hydrophobic neem oil, the part left after azadirachtin is extracted, and it smothers insects by blocking their breathing openings. Azadirachtin is the part that repels insects and disrupts the hormones that control their growth and reproduction. The active ingredient on the label tells you which group a bottle belongs to.
Look before you buy, because neem oil is matched to a pest. A ten-power hand lens shows insects, webbing and eggs on the tops and undersides of leaves, and on the points where leaves join stems, where mealybugs gather. A shiny, sticky film on the leaves and on the table underneath comes from aphids, mealybugs or scale insects, and armored scales are the exception because they leave none.
Colorado State University rates neem oil and neem insecticides separately for houseplant pests, and the ratings differ by pest. A rating of suppress means the spray may lower pest numbers without clearing the plant.
| What you see | Likely pest | Clarified neem oil | Azadirachtin product | First move |
|---|---|---|---|---|
| White flecks, a gray or bronzed look, fine webbing | Spider mites | May suppress | Not effective | Wash the leaves with a jet of water and raise the humidity |
| White cottony tufts on leaf undersides and where leaves join stems | Mealybugs | May suppress | Not effective | Lift them off with tweezers or dab with an alcohol swab after testing one leaf |
| Brown, gray or white shell-like bumps on stems and along leaf veins, sometimes with honeydew | Scale insects | May suppress | Not effective | Rub or scrape them off with a fingernail file |
| Tiny white insects that flutter up when you touch the plant | Whiteflies | Controls nymphs, not adults | Controls nymphs, not adults | Hang yellow sticky cards for the adults |
| Small, soft insects clustered on new growth and just below flower buds | Aphids | May suppress | May suppress | Spray with a vigorous jet of water or crush them |
| Small, dark flies hopping over the soil surface | Fungus gnats | Not effective | Controls larvae, not adults | Let the soil surface dry between waterings |
Fungus gnats need a treatment that reaches the soil, and the bacterial insecticide Bti is highly effective as a soil drench. Some neem products are labeled for soil drench and can control the larvae, but a leaf spray does not become a soil treatment. The fungus gnat guide covers the whole approach.
The first moves in the table clear many minor infestations on their own, and University of New Hampshire Extension treats neem oil like any other pesticide, as a last resort.
Which houseplants can neem oil burn?
Neem oil can burn the foliage of any plant, which is why UNH Extension suggests testing a small area first, but some leaves react more than others. If your plant fits a row below, begin with a nonchemical method.
| Plant group | Why it is at risk | Safer approach |
|---|---|---|
| Hairy or fuzzy leaves, such as African violet | Hairy leaves hold oil longer, which makes them more sensitive | Remove pests by hand or with a gentle rinse, and test a leaf if you do spray |
| Ferns and palms, such as Boston fern | Both have known potential for oil damage | Rinse pests off with water in a sink or shower |
| Blue- or gray-colored foliage, such as a potted eucalyptus | Oil removes the leaf wax that creates the color | Wipe or pick off the pests instead |
| Plants that are dry, wilted or just repotted | Oils should not go on drought-stressed plants or new transplants | Water the soil a day or two ahead, and hold off on a plant that was just repotted |
Other plants may be sensitive too, and a plant can show sensitivity at one time of year and not another, so repeat the small test when you spray in a different season. If the label names your plant as one to avoid, skip that product.
How do you prepare the plant and the room?
Move the infested plant away from your other plants as soon as you confirm a pest, and wash your hands after you touch it so the pest does not travel on them.
Water the soil a day or two before you spray, because no pesticide should go on a moisture-stressed plant. Choose a day when the air is between about 50 and 85°F, since oil sprays can damage plant tissue outside that range.
Then spray one or two leaves at the label rate and look at them over the next one or two days for spots, browning or curl. Treat the whole plant only if those leaves look normal.
Spray outdoors when you can, so the residue disperses outside and your furniture and household are not exposed. In cold weather, spray indoors in a well-ventilated area, or seal the plant in a plastic bag with a small hole cut for the nozzle.
Oil should also stay off a plant that had sulfur on it in the past 2 to 4 weeks, because dead foliage may result.
Before you spray
- Gloves and any other protective equipment the label requires
- Only as much mix as you will use that day, if the product needs diluting
- The spray kept away from aquariums, since neem oil is slightly toxic to fish
How do you apply neem oil to a houseplant, step by step?
Whitefly nymphs feed on the leaf undersides and mealybugs gather where leaves join stems, so the spray has to reach the places the insects hide.
- Clear what you can firstUse the first move from the table for your pest, then prune the worst-infested parts so the oil has less to reach.
- Check the label and mixConfirm that your plant and the pest are both listed. The neem oil mixing guide covers diluting a concentrate.
- Spray every surfaceThe oil works only where it covers, so wet the tops and undersides of the leaves, the stems and the joints where leaves meet the stem until the plant is completely covered.
- Let it dry in the shadeKeep the plant out of direct sun until the leaves are dry.
- Wash up and store the productWash your hands and any equipment, then store or dispose of leftover mix as the label directs.
How often do you repeat neem oil, and how do you know it worked?
Even on immature insects, neem oil does not give immediate results, and a repeat spray may be needed to bring the population down. A contact oil kills only the insects it covers, so pests that were hidden or that hatch afterward are still on the plant. Spider mite eggs hatch within a couple of days, and whitefly eggs hatch in three to seven days.
The label sets the repeat interval. Nevada Extension notes that fungi may need neem repeats at seven- to 10-day intervals, and insects more often.
Before each repeat, check the same spots with the hand lens.
- Live pests on the leaf undersides and stem joints
- New webbing or fresh sticky honeydew
- Scale bumps that are soft and flexible to the touch, since those may still be alive
Scales killed by oil can stay stuck to the stem and look like living ones, so a bump alone does not show that the spray failed.
If the pest is still there after the repeats the label allows, recheck the diagnosis against the table above, since neem oil is not effective against fungus gnats or adult whiteflies.
When a plant is heavily infested and badly damaged, throwing it away is necessary and economical, and it avoids exposing your other plants to the same pest.
What do you do if the leaves look burned after spraying?
Oil damage shows up as spots, yellowing, browning or leaf loss, and neem oil can burn foliage. Stop spraying that plant.
The same marks also come from other causes, so check those before blaming the oil. Brown or scorched leaf tips can come from overwatering, dry soil, or too much fertilizer or salts, and leaf spots and blotches can come from sunburn after a recent move or from chilling below 50°F.
Pro Tips
- Identify the pest with a ten-power hand lens before buying any product.
- Check that both your plant and your pest are on the product label.
- Spray one or two leaves first and watch them for one or two days before treating the whole plant.
- Cover the leaf undersides, the stems and the joints where leaves meet stems.
- Spray outdoors when you can, between about 50 and 85°F, and keep the plant out of direct sun until it dries.
- Keep an infested plant away from your others while you treat it.
Frequently Asked Questions
Can neem oil treat powdery mildew on houseplants?
It can help limit the spread. Neem oil works against some fungal diseases such as powdery mildew by preventing spores from germinating and entering leaf tissue, but it does not cure a plant that is already infected. Confirm the diagnosis, and use only a product whose label lists powdery mildew on your plant.
Should I add dish soap to neem oil?
Only if the product label tells you to. Homemade soap mixes can burn plants, and dishwashing detergents carry a risk of plant injury.
Does neem oil kill fungus gnats?
A neem oil spray on leaves is not effective against fungus gnat larvae or adults, because the larvae live in the potting soil. Let the soil surface dry between waterings, and use a Bti soil drench or a neem product labeled for soil drench to treat the larvae.
Is neem oil safe around cats?
Keep pets away from wet leaves and from the concentrate. Neem oil can be slightly irritating to the eyes and skin. In other countries, some cats treated with neem oil for fleas had adverse reactions including trembling and convulsions, and some died, though most recovered within 1 to 5 days. Call your veterinarian if a pet touches or licks the spray.
How long should a new plant stay apart from the others?
Sources differ. Minnesota Extension suggests one to two weeks to let pest problems show, while Colorado State suggests at least three weeks, because scale, mealybugs and whiteflies almost always arrive on newly bought or gifted plants.
Sources & References
- University of Minnesota Extension, Managing Insects on Indoor Plants
- Colorado State University Extension, Managing Houseplant Pests
- University of New Hampshire Extension, What Should Neem Be Used for on Plants?
- UC Statewide IPM, Houseplant Problems
- National Pesticide Information Center, Neem Oil General Fact Sheet
- Washington State University Hortsense, Herbicide Damage: Horticultural spray oil
- University of Maryland Extension, Pesticide Profile: Horticultural Oil
- Rutgers Plant & Pest Advisory, A Primer on Dormant Oil Applications
- University of Nevada Extension, Horticultural Oils
