8 Natural Insecticides That Won't Harm the Earth

Oct 17, 2024

These natural, DIY formulas are safe yet effective for helping rid your garden of pests.

Treehugger / Julie Bang

Natural pesticides can be an excellent tool in your arsenal against insect pests, which have the potential to turn your lush garden into their own insect all-you-can-eat buffet. Fortunately, making them yourselves doesn't have to be super complicated.

It's important to note that just because these are "natural" or homemade insecticides, that doesn't imply that they can't harm your soil, your garden, or your person. An insecticide (which is a pesticide) is defined by the EPA as "any chemical used to prevent, destroy, repel, or mitigate pests," and as such, they have the potential to be "harmful to people, animals, or the environment." And, of course, not all insects are harmful. Applying insecticides indiscriminately, especially harsh pesticides that affect even the beneficial insects, can have a detrimental effect on your local garden ecosystem.

Some plants may be more sensitive than others to various treatments. We recommend testing for plant sensitivity. Simply apply the formula to a small area and wait 24 hours to see if any damage occurs.

Before going all out with any pesticide or insecticide, be sure to do your homework and choose the option that is both most effective and least harmful to you and your garden.

The best pest management plan always starts with preventative and other non-chemical methods before bringing out the sprays. Since healthy, happy plants are much more resilient to pests, always begin by choosing the right plants for the right places and caring for them correctly.

Companion planting is another essential strategy in pest control. It involves selecting plants that will be good neighbors to one another—improving environmental conditions, attracting beneficial insects and creatures, and/or repelling, confusing, or distracting certain pest species to keep their companions safe.

LEARN MORE: What Is Companion Planting?

A homemade, natural pesticide made from vegetable oil mixed with a mild soap (such as Dr. Bronner's Castile soap) can have a devastating effect on certain troublesome insects, such as aphids, mites, thrips, etc.

To make a basic oil spray insecticide, mix one cup of vegetable oil with one tablespoon of soap (cover and shake thoroughly), and then when ready to apply, add two teaspoons of the oil spray, mix with one quart of water, shake thoroughly, and spray directly on the surfaces of the plants which are being affected by the pests.

The oil coats the bodies of the insects, effectively suffocating them, as it blocks the pores through which they breathe.

A very similar homemade, natural pesticide to the oil spray is a soap spray, which is also effective for controlling spider mites, aphids, scale crawlers, mealybugs, whiteflies, beetles, and other hungry insects.

To make a basic soap spray insecticide, mix one and one-half teaspoons of mild liquid soap (again, Castille soap is good here, as it's gentle and all-natural) with one quart of water, and spray the mixture directly on the infected surfaces of the plants.

A soap spray insecticide works in a similar fashion as an oil spray pesticide and can be applied as necessary. Note: It is always recommended to NOT apply it during the hot sunny part of the day, but rather in the evenings or early mornings).

Both soaps and oils can harm plants if applied when plants are water-stressed, temperatures are above 90 degrees, if they are sprayed in direct sunlight, or when high humidity does not allow for rapid drying.

Meanwhile, some plants are sensitive to oil or soap sprays, including (but not limited to):

Portulaca (Portulaca grandiflora), hawthorn (Crataegus spp.), sweet pea (Lathyrus odoratus), cherries (Prunus spp.), plum (Prunus spp.), horse chestnut (Aesculus hippocastanum), mountain ash (Sorbus spp.), Japanese maple (Acer palmatum), bleeding heart (Lamprocapnos spectabilis), maidenhair fern (Adiantum spp.), crown of thorns (Euphorbia milii), lantana (Lantana camara), nasturtiums (Tropaeolum spp.), gardenias (Gardenia jasminoides), and Easter lilies (Lilium longiflorum).

An oil extracted from the seeds of the neem tree is a powerful natural pesticide, capable of disrupting the life cycle of insects at all stages (adult, larvae, and egg), making it a great resource for the organic gardener.

Neem oil acts as a hormone disruptor and as an "antifeedant" for insects that feed on leaves and other plant parts. Neem oil is biodegradable and nontoxic to pets, birds, fish, and other wildlife, and is effective against a variety of common garden insect pests. It's also a natural fungicide that can combat powder mildew and other fungal infections on plants. Neem oil can be found at many garden stores or natural foods markets.

To use neem oil as a natural pesticide, either follow the instructions on the bottle, or start out with a basic mixture of two teaspoons of neem oil and one teaspoon of mild liquid soap shaken thoroughly with one quart of water, and then sprayed on the affected plant foliage. Neem oil can also be used preventatively by spraying the leaves of plants that are often ravaged by pests before they're actually infested.

Treehugger / Sanja Kostic

This natural substance with a somewhat unwieldy name is made from a sedimentary rock created by fossilized algae (diatoms), and which is a rather abundant resource (diatomaceous earth is said to make up 26 percent of the earth's crust by weight).

Diatomaceous earth has many uses in and around the home, and acting as a natural pesticide is just one of them. This material works not by poisoning or smothering the insects, but instead by virtue of its abrasive qualities and its affinity for absorbing the lipids (a waxy substance) from insects' exoskeleton, which then dehydrates them.

Diatomaceous earth is often available at garden stores (although many times only in large bags), so if you have a small yard, consider splitting it with a neighbor. To apply, simply dust the ground around your plants or even sprinkle it on the foliage, where it will help control snails and slugs as well as other crawling insects. Due to its dried nature, to be an effective natural pesticide, diatomaceous earth needs to be reapplied after every rain.

Garlic is well-known for its pungent aroma, which is delectable to some and yet repellent to others, and it is this strong scent that comes into play when used as a natural pesticide. Actually, it's not really clear if garlic spray and chile spray (below) are actually insecticides or are more likely insect repellents, but either way, these common kitchen ingredients can be used to knock down, or even knock out, insect infestations in the garden.

To make a basic garlic spray, take two whole bulbs (not just two cloves) and puree them in a blender or food processor with a small amount of water. Let the mixture sit overnight, then strain it into a quart jar, adding one-half cup of vegetable oil (optional), one teaspoon of mild liquid soap, and enough water to fill the jar. To use this natural pesticide, use one cup of mixture with one quart of water and spray liberally on infested plants.

Similar to garlic spray, chile pepper spray is a great homemade, natural insect repellent that can be used for a variety of different pests. Chile spray can be made from either fresh hot peppers or chile pepper powder.

To make a basic chile spray from pepper powder, mix one tablespoon of chile powder with one quart of water and several drops of mild liquid soap. This natural pesticide can be used full-strength on the leaves of affected plants. To make chile spray from fresh chile peppers, blend or puree one-half cup of peppers with one cup of water, then add one quart of water and bring to a boil. Let sit until cooled, then strain out the chile material, then add several drops of liquid soap to it. Spray as desired.

Hot chile peppers can be very potent for humans as well. Be sure to wear gloves when handling them, and keep any sprays that use them away from the eyes, nose, and mouth.

From the folks at Rodale's Organic Life comes this all-in-one DIY natural pesticide, which is said to be a combination of many different recipes submitted by readers.

To make it, puree one bulb of garlic and one small onion, add one teaspoon of cayenne pepper powder, and let steep for an hour. Strain the mixture and add one tablespoon of liquid soap and mix well. To apply this homemade pesticide, spray it full-strength onto both the upper surface of the leaves, as well as the undersides. Store the remainder in the refrigerator for up to a week if desired.

Tomato plants are part of the nightshade family, and as such, contain alkaloids such as the aptly named "tomatine," which can effectively control aphids and other insects. To make tomato leaf spray for a natural pesticide, chop two cups of fresh tomato leaves (which can be taken from the bottom part of the plant) into one quart of water, and let steep overnight. Strain out the plant material and spray onto plant foliage.

Although there are many more natural pesticides available, such as Bt (a soil microbe toxic to certain insects), milky spore (also a microbe), nicotine (extracted as a tea from bulk tobacco), pyrethrum (derived from a variety of daisy), and iron phosphate (a natural mineral toxic to slugs and snails), the above natural pesticide recipes should give you a good starting point for creating your own version. Every organic gardener seems to have their own particular blend and ratio of ingredients, so by paying close attention to the effects of a specific recipe, it's possible to modify it to best suit your own insect battles.

Just remember, killing off all of the insects in your garden is not the desired result here, as any healthy ecosystem requires an abundance of beneficial insects, microbes, and fungi, both in the soil and on the plants themselves. To that end, encouraging other predatory insects (ladybugs, praying mantis, etc.) and creating good habitat for them, as well as building soil fertility, can also be an effective pest management approach.

READ NEXT: The Most Common Mistakes Gardeners Make with Organic Pest Control

Leong SC, Abang F, Beattie A, Kueh RJ, Wong SK. Impacts of horticultural mineral oils and two insecticide practices on population fluctuation of Diaphorina citri and spread of Huanglongbing in a citrus orchard in Sarawak. ScientificWorldJournal. 2012;2012:651416. doi:10.1100/2012/651416

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National Pesticide Information Center. Diatomaceous earth. Updated January 2013.

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