How To Use DIY Neem Oil Without Harming Bees

Recent research questions common wisdom that neem oil is harmless to bees.

hand shows off DIY neem and castile soap spray as natural insecticide in front of window

Treehugger / Lexie Doehner

Overview
  • Working Time: 10 minutes
  • Total Time: 20 minutes
  • Skill Level: Beginner
  • Estimated Cost: $15.00

Neem oil is a vegetable oil from the seeds and fruit of the neem tree Azadirachta indica, native to India, Southeast Asia, and some parts of Africa. It has long been used in traditional Ayurvedic medicine as a skin and hair treatment but is also increasingly used today as an insecticide.

You can find dozens of websites touting its benefits, and indeed, it is an effective and organic insecticide. Neem oil can kill insects directly, but its main ingredient interferes with insects' normal life cycle because it is similar to insect hormones, so it acts as a deterrent to growth and reproduction. Neem oil is also a fungicide and can improve the quality of soil for agricultural uses.

Neem Oil Is Organic, But Is It Safe?

snake houseplant, spray bottle, neem oil, and castile soap sit on kitchen counter near window

Treehugger / Lexie Doehner

Most recommendations of neem oil found online consider it to be generally environmentally friendly and harmless. Some scientific research backs this up, such as a finding that neem oil applications “pose little risk of harm to decomposer invertebrates” like earthworms. But scientific evidence is usually lacking among the recommendations online, and a recent review of the scientific literature warns that “little is known about the non-target toxicity of neem-based insecticides.”

While much of the research that exists reports no adverse environmental effects, specific studies suggest that over-spraying of neem oil can lead to runoff and accumulation in waterways, resulting in adverse effects on aquatic organisms, including plankton and fish, and on birds such as quail.

Studies of the effect of neem oil on bees have made neem oil controversial for outdoor use, including the recommendation by one leading study that its use “should be avoided in crops during the flowering stage when the plants are visited by bees.” Recent research shows evidence of an anti-feeding effect in some bee species, and reduced reproduction rates and increased queen bee mortality in others. Results do vary depending on the concentration level of neem oil in the insecticidal solution, but as one study warns, “[a]ll of these factors could potentially compromise colony survival.”

a large bee rests on fallen leaves on dirt in patch of sunlight

Treehugger / Lexie Doehner

Neem oil is usually applied in two ways. As a foliar spray, it can cause pests to suffocate, bees included. As a systemic insecticide, plants' roots take up the oil into their tissues, and when pests ingest plant tissue, the active ingredient of neem oil, azadirachtin, interferes with their normal reproductive life cycle. This same effect happens when bees ingest pollen and bring it home to their hives, disrupting the colony or even killing the queen.

As a result, given the worldwide threat of colony collapse disorder and the important role that bees play in the production of food, this article recommends using neem oil only on indoor plants. For outdoor use, there are alternatives.

Alternatives to Neem Oil for Outdoor Use

There are pollinator-friendly alternatives to neem oil outdoors, such as olive oil mixed with organic Castille soap to suffocate pests such as rose slugs or aphids; Bt, a bacterial toxin, to kill caterpillars; or products containing the active ingredient Bacillus subtilis, to control fungi like black spot and powdery mildew. It's always best to apply any insecticide at dawn or dusk, before or after bees and other pollinators are feeding. If you see bees, put the sprayer away.

Before you buy a commercial product containing neem oil, as always read the label, as many contain a multitude of ingredients that may or may not be suited for indoor use. It's much easier to make your own neem oil spray.

What You'll Need

Tool

  • 1 quart-size spray bottle

Materials

  • 1 quart (1L) water, plus extra for initial spraying
  • 1 1/2 teaspoon (7.5 mL) crude or raw (100% pure) organic neem oil
  • 1 teaspoon (5mL) liquid Castile soap or dish detergent

Instructions

  1. Combine Ingredients

    hand adds castile soap to neem oil mixture for plants in reusable bottle

    Treehugger / Lexie Doehner

    Add 1-quart water and 1 tsp. soap to the spray bottle. Slowly stir in the neem oil, then shake the bottle well.

  2. Remove Sunlight

    potted snake houseplant sits on kitchen counter next to stove and window

    Treehugger / Lexie Doehner

    Remove any plants from direct sunlight before spraying, preferably to a washable surface like a kitchen floor or counter.

  3. Spray Plants

    hand sprays diy neem oil on snake houseplant as insecticide

    Treehugger / Lexie Doehner

    Spray plants on both sides of the leaves.

  4. Return to Sunlight

    snake houseplant in concrete planter sits next to sunny window and diy neem oil spray

    Treehugger / Lexie Doehner

    Once the neem oil is dry, return any plants to direct sunlight.

  5. Repeat

    hands inspect leaves of snake houseplant for insects to spray neem oil

    Treehugger / Lexie Doehner

    Repeat weekly until there are no signs of pests.

Frequently Asked Questions
  • Why is neem oil potentially dangerous to bees?

    When sprayed, neem oil can suffocate bees. When the oil penetrates the plant roots, bees can also ingest it, and the azadirachtin it contains can disrupt their reproductive cycles.

  • What does neem oil do for houseplants?

    Neem oil helps stave off pests—like aphids, mites, beetles, and leafhoppers—and diseases like powdery mildew and root rot.

  • What's the best water-to-neem oil ratio?

    The best ratio for this DIY plant spray is one part neem oil to 133,000 parts water, or a teaspoon and a half of neem oil to one quart of water.

View Article Sources
  1. Pascoli, Mônica, et. al. “Neem Oil Based Nanopesticide as an Environmentally-Friendly Formulation for Applications in Sustainable Agriculture: An Ecotoxicological Perspective.” Science of the Total Environment, vol. 677, 2019, pp. 57–67., doi:10.1016/j.scitotenv.2019.04.345

  2. Kreutzweiser, David, et. al. “Environmental Safety to Decomposer Invertebrates of Azadirachtin (Neem) as a Systemic Insecticide in Trees to Control Emerald Ash Borer.” Ecotoxicology and Environmental Safety, vol. 74, no. 6, 2011, pp. 1734–1742., doi:10.1016/j.ecoenv.2011.04.021

  3. Mužinić, Vedran and Želježić, Davor. “Non-Target Toxicity of Novel Insecticides.” Arhiv Za Higijenu Rada i Toksikologiju, vol. 69, no. 2, 2018, pp. 86–102., doi:10.2478/aiht-2018-69-3111

  4. Murussi, Camila R, et. al. “Azadirachtin, a Neem-Derived Biopesticide, Impairs Behavioral and Hematological Parameters in Carp (Cyprinus carpio).” Environmental Toxicology, vol. 31, no. 11, 2016, pp. 1381–1388., doi:10.1002/tox.22143

  5. de Souza Góis, Rayr Cezar, et. al. “Reproductive Toxicity of Neem Seeds (Azadirachta indica) in Male Quail (Coturnix coturnix japonica).” Ciência Rural, vol. 49, no. 11, 2019., doi:10.1590/0103-8478cr20180484

  6. Xavier, Vânia M., et al. “Acute Toxicity and Sublethal Effects of Botanical Insecticides to Honey Bees.” Journal of Insect Science, vol. 15, no. 1, 2015, pp. 1–6., doi:10.1093/jisesa/iev110

  7. Bernardes, Rodrigo C., et. al. “Azadirachtin-Induced Antifeeding in Neotropical Stingless Bees.” Apidologie, vol. 48, 2017, pp. 275–285., doi:10.1007/s13592-016-0473-3

  8. Goktepe, Ipek and Plhak, Leslie C.. “Comparative Toxicity of Two Azadirachtin-Based Neem Pesticides to Daphnia pulex.” Environmental Toxicology and Chemistry, vol. 21, no. 1, 2002, pp. 31–6., doi: 10.1002/etc.5620210105

  9. González-Gómez, Rebeca, et. al. “Effects of Neem (Azadirachta indica) on Honey Bee Workers and Queens, while Applied to Control Varroa destructor.” Journal of Apicultural Research, vol. 55, no. 5, 2016, pp. 412–421., doi:10.1080/00218839.2016.1260239