Claudette Sims – Halton Master Gardener

With recipes galore on the Internet and social media, it’s not surprising to see so many recommendations for homemade pesticides and herbicides. We need to rethink these practices to ensure that we are making the right choices for our gardens and the environment. What does Health Canada have to say about homemade pesticides?

Health Canada advises consumers to be aware that preparing, storing, and using homemade pesticides may pose health and environmental safety risks. Homemade pesticides do not undergo any scientific evaluation and do not have label directions that the user can follow to ensure safe use or effectiveness. While some recipes, such as mixtures of soap and water, are not likely to pose human health risks, other recipes that require cooking and boiling may pose health or environmental concerns.

The Risks of Homemade Pesticides – HEALTH CANADA

When a home remedy is used to deal with a plant issue:

  • there are no labels that tell you how much, where, when to apply, or how often. This may result in overuse and harm to people, pets, and the environment.
  • no guidance is provided regarding wearing gloves or protective clothing. For example, pepper sprays can be very potent if they get in your eyes or on your skin.
  • first aid directions are absent if a child or pet accidently comes into contact with the substance. Also missing will be the effect on the surrounding environment, such as harming bees or making the soil toxic.

Ingredients may seem ‘better’ because we’re familiar with them but they can also contain additives that are harmful. If cooking and/or mixing is required, you may be exposed to toxic fumes. Finally, cooking utensils can be contaminated in the process of preparing a home remedy.

Sprays are used for a REASON

We often hear from gardeners who spray plants without knowing WHY they are spraying. Ask yourself some questions before reaching for any spray bottle.

  • Is there a disease issue? If so, what is the disease?
  • Have you spotted a “bug”? Is that bug a friend or a foe?
  • Is plant damage cosmetic or serious enough to harm the plant?

Many plant diseases are better controlled by changing cultural practices, e.g., avoiding overhead watering, pruning to encourage air circulation.

Most bugs just eat other bugs. You need to have a positive ID on an insect or disease BEFORE you spray. By randomly spraying, you may be destroying the very bugs that will keep your garden in balance.

Assess the damage on your plant. Is it mostly cosmetic, or serious enough to harm the plant? Plants are meant to be eaten – the monarch caterpillar is a good example of an insect that most gardeners welcome in their garden. If you have holes in leaves, it means your garden is alive.

“I Don’t Want to Use Chemicals”

This is admirable idea, but everything is a “chemical”. Water is a chemical-literally H2O – 2 hydrogen atoms and one oxygen. Homemade sprays aren’t better because they use “natural” ingredients-those are still chemicals. They can be just as deadly as commercial sprays. For instance, ammonia is sometimes recommended for killing slugs around hostas. But it will also kill all the important soil biota that your plants need to survive and can kill beneficial animals like frogs. (See: Controlling Slugs with Ammonia – Which Methods Work?). Plus it may only be effective (if at all) at high concentrations.

Homemade Soap Sprays

Homemade soap sprays at the wrong concentration can cause phytotoxicity – burning leaves. Garden Myth: Dishwashing Liquid as an Insecticide Image: Laidback Gardener

Homemade soap sprays are not the same as commercial insecticidal soaps. Commercial sprays are based on fatty acids chosen to reduce phytotoxicity (e.g. adverse plant effects). Many household dish washing products are detergents and not soaps. Many contain other ingredients such as perfume or grease cutting agents. They can do damage to foliage and soil. Commercial insecticidal soaps are very reasonably priced and far superior to homemade recipes. They can be purchased as sprays or in concentrated form. Trust me, they are way better than homemade.

(See: So, What Exactly Is Insecticidal Soap?)

Keep in mind that insecticidal soaps, whether commercial or homemade will kill non-target beneficial insects as well. Commercial insecticidal soaps are excellent for dealing with difficult pests like mealy bugs and scale on houseplants, but should be used with caution outdoors.

Baking Soda (Sodium Bicarbonate/SBC)

I still see baking soda recommended to treat powdery mildew despite the fact that research does not support its use for powdery mildew and other fungal diseases and instead shows it is more likely to harm plants. “Baking soda itself is not likely to control fungal disease in your garden or landscape, but very easily could cause leaf damage if used at a higher concentration.” “While SBC efficacy increases with concentration, so do the phytotoxic effects, presumably due to sodium content. Stored fruits can experience weight loss and undesirable aesthetic alterations such as changes in color or presence of SBC residues with as little as 2 percent SBC. Phytotoxicity is even more problematic on foliage, where even a 1 percent SBC solution can cause severe foliar damage, including interveinal chlorosis”. “Other treatments have been more successful in powdery mildew control, including horticultural oils, potassium bicarbonate, potassium phosphate, sulfur, milk, and even water sprays.” Dr. Linda Chalker-Smith (see: Miracle, Myth or Marketing: Baking soda – will fungi fail and roses rejoice? L. Chalker-Scott)

Insecticidal soaps are only recommended after all other options are tried and have failed.

If you have powdery mildew issues, I would recommend that you start with a simple water spray on leaves (I know this sounds counterintuitive, but there is research to support it) or use a milk spray, both of which have proven successful and do not harm plants or the environment. “Most recently, a spray made of 40% milk and 60% water was as effective as chemical fungicides in managing powdery mildew of pumpkins and cucumbers grown in mildew-prone Connecticut.” (see: Using Milk to Prevent Powdery Milkdew – Grow Veg.).

Vinegar (Acetic acid)

Vinegar is another homemade herbicide which is often recommended for killing weeds. It’s true that vinegar (Acetic acid) is allowed under the pesticide act as a herbicide. However, household vinegar typically contains 5 to 8% acetic acid by volume with pickling vinegars having the higher acid content. At these concentrations, vinegars usually only kill top growth, leaving the root unaffected. Gardeners may think vinegar is effective because the weeds initially die down, but they are more than likely to regrow. (See: Vinegar: A Garden Miracle– Garden Professors). The commercially available herbicides for domestic use containing acetic acid often contain additional ingredients, such as surfactants, that make the product more effective. There are many products registered containing acetic acid -some are for domestic use. You can search products here: Health Canada – Consumer Product Safety.

Hydrogen Peroxide

Just two of many fungicides commercially available.

Hydrogen peroxide is another homemade remedy for fungal issues. It certainly has antifungal properties, but it can also be phytotoxic (poisonous to plants) at levels required to control pathogens and thus is typically not recommended. Peroxide may work in some cases, but the problem is knowing in which case it works, when to spray and what concentration to use. That information is very difficult to source reliably. There are many reliable fungicides available that have been tested by Canadian scientists for use on plants.

Rubbing Alcohol (Isopropyl Alcohol)

Use rubbing alcohol to disinfect garden tools.

Rubbing alcohol is sometimes recommended as a spray. It can be effective to control scale insects if applied with a cotton swap directly on the insect. However, it should not be used as a foliar spray. It is however, excellent to use as a disinfectant for garden tools.

“Master Gardeners should be recommending effective homemade recipes instead.” “They should not be recommending products like glyphosate”

Sometimes our message against homemade recipes gets interpreted as being in favour of commercial pesticide products like glyphosate. Glyphosate (Round up) is not approved for cosmetic use to treat things like weeds in lawns, so Master Gardeners would not recommend it. Glyphosate is allowed on plants that are concerns for human health such as poison ivy, and yes we might recommend it for that use if it is warranted.

Recommending the use of commercial insecticidal soaps also does not mean that we endorse the indiscriminate use of pesticides. We recommend commercial products because they are effective, have gone through rigorous testing and include directions and warnings for use. Many homemade recipes are not effective, can harm plants and the environment. We’ve seen the harm they do when members post images of plants killed or damaged by homemade sprays. Gardeners are encouraged to use registered products that have been rigorously tested, has instructions for use and warnings about potential issues.

In Conclusion

Beneficial insects may be harmed when using any pesticide. A ground beetle (photo) eats slugs and many pest larvae such as gypsy moth larvae, cankerworms, army worms, cutworms, and snails
Image: Canadian Wildlife Federation

Consider managing your garden without pesticides. You might be surprised to find beneficial lady bugs chomping at your aphids. If you must use a spray in your garden, make sure you know why you’re spraying by identifying the issue. Use the correct spray approved for the particular disease or pest. Many pests in the home and garden can be managed without pesticides. In a garden, grow plants suited to the environment and keep them healthy with proper irrigation and fertilization. Pests and disease occur with greater occurancy on stressed plants (ie., planted in the wrong environment – soil, light and moisture). Weeds of course, can be controlled by hand-pulling, mulching, or weeding tools.

More myths and Ineffective Treatments

Eggshells Do Not Deter Slugs

Here’s a fun video to watch!

Also check out this video:

How To Get Rid of Slugs 🐌🐌🐌 Do Eggshells Work? – Garden Myths

Other Common Myths


search previous next tag category expand menu location phone mail time cart zoom edit close