Ask gardeners about homegrown pest control and you'll get a slew of creative responses: beer-filled dishes to attract slugs, a spray of juiced bugs to deter insect relatives, marigolds planted to repel nematodes, and so on. Will these strategies work in your school garden? Which are most effective for which pests? What is the scientific explanation, if any, for the effectiveness of each approach? Might any techniques be harmful to plants or beneficial insects? Such questions are rife with possibilities for student inquiry. Consider inviting your students to interview gardeners in your community and/or examine books or Internet sites in search of suggestions for companion plants and homemade pest remedies. Then set up some investigations to test their effectiveness. Be sure that your sleuths have observed carefully enough to see the creatures that are actually doing damage and have positively identified the culprits.
With companion planting, pest control is often the aim, but better space and nutrient efficiency can also result. Beneficial insects, such as ladybugs, depend on pests for nourishment. But when pests are in short supply, certain plants that offer nectar and pollen offer these good guys an alternative food source. Many of these are small-flowered plants that belong to the carrot and daisy families (anise, dill, fennel, yarrow, zinnia). Other companion plants repel harmful insects, or attract them and draw them away from your precious plants.
Following are some classic recipes for homemade insect sprays. Be sure to have students test such solutions on a few small leaves before starting a full-scale application and keep labeled containers tightly sealed in a safe place.
Homemade Soap Sprays. These can be effective against soft-bodied insects such as aphids. Dissolve 3 tablespoons of soap flakes (not detergent) in a gallon of water and spray on plants.
Herbal Insect Repellent. Gather leaves from tansy, lavender, and sage, which have strong insect-repelling qualities. You'll need an ounce of leaves from each plant. Place the herbs in a 1-quart jar and fill it with boiling water. Let it set until it cools. Or make an infusion by steeping the herbs in a jar of water placed in a sunny outdoor spot. Drain off the liquid and set this solution aside. Dissolve 1 teaspoon of soap flakes in 2 cups of water. Add 1/8 cup of the herb solution and mix well. Use a sprayer to coat all plant parts with the bug repellent.
Hot and Spicy Spray. Some gardeners combine hot peppers and garlic in a soapy solution. Puree two hot peppers and two cloves of garlic in a blender. Add 3 cups of water and 2 tablespoons of biodegradable liquid soap. Strain and fill a spray bottle with the solution.
Bug Juice. Although it seems a bit macabre, consider using bug juice to fight pests. Collect at least 1/2 cup of pesky insects and place them in an old blender with enough water to make a thick solution. Blend on high and strain out the pulp using cheesecloth or a fine sieve. Dilute at a rate of 1/4 cup bug juice to 1 cup of water, pour into a spray bottle, and apply to plants. (Some scientists believe that pheromones from the blended insects send a warning to their living relatives!)