How to make horticultural soaps and insecticidal sprays
There is no magic bullet for keeping your garden and indoor plants free from insect pests. Some tricks I have learned over the years are ways to cope with bugs without resorting to nasty chemicals. Here are my tips, including homemade insecticidal sprays (soap sprays).
Pay Attention to Your Plants
Before resorting to using pesticides (even organic ones), consider the following techniques to discourage insect pests from attacking your plants:
- Nourish your plants with organic amendments such as aged compost. Strong plants don't attract as many insects and can withstand their assault better than weak ones. If you're using fertilizer, follow instructions closely. Over-fertilized plants will attract pests to eat their lush new growth.
- Use companion planting to repel insects naturally. Some plants thrive together; some do not. See our Companion Planting Guide.
- Use barriers like row covers to block pests from attacking your plants, especially tender transplants. (Remove the covers when plants are established and in bloom to allow for insect pollination.) Additionally, "collars" (paper towel or toilet paper cardboard rolls) inserted around the small transplants (1 to 2 inches into the soil) will prevent insects such as cutworms from eating the young stems.
- Time plantings to avoid peak insect populations. For example, plant squash as early as possible to avoid squash vine borers, which lay eggs in early to mid-summer. Plant carrots after June 1 and harvest by early September to avoid the carrot fly.
- Select varieties that are naturally resistant to some pests. I grow a lot of butternut squash because it is highly resistant to attack from the squash vine borer.
- Make your garden welcoming to beneficial insects and they will do a lot of the work for you by keeping the bugs they feed on in check. For example, lady beetles are an effective biological control of many insect pests. If you see a tomato hornworm with white cocoons on his back (above photo), leave him alone. A parasitic wasp has laid her eggs on him and soon her babies will eat him from the inside out. A fitting death for such a gruesome pest!
- Learn to identify the bugs in your garden. You can't beat them if you don't know who is friend and who is foe. Learn what their larvae and eggs look like to head them off before they become adults.
These aphids have done some damage, but don't spray if you see the black and orange alligator-like ladybug larvae attacking them. He will do the dirty work for you by eating up to 50 aphids a day!
5 Organic Pesticide Sprays for Insects
If you have exhausted all these methods and feel you must resort to using a spray, don't reach for harsh chemicals. They will do more harm than good by polluting the watershed, killing good and bad bugs alike, and eventually the insects you are trying to kill may grow resistant to those chemicals requiring you to use even stronger ones! They can also harm birds, animals, you, and your children!
Try a more natural approach by making one of these homemade insecticidal sprays. Bear in mind that although they are less toxic they are not totally harmless. Keep them away from kids and pets. Test them on a few leaves before you go all in to make sure they won't injure your plants. Be sure never to spray them on your plants during the sunny, hot part of the day or they will definitely cause foliar damage. Spray in the evening, when bees and other pollinators are not active.
- Dish Soap Spray: Dissolve 1 tablespoon of a mild liquid soap such as a pure dish soap (no bleach, degreaser, or detergents added) or castile soap in 1 quart of water. Dr. Bronner's soap may be expensive, but it uses no animal fats, which makes it a good choice for vegans. Insecticidal soaps are good for killing soft-bodied insects. Be sure to cover the whole plant—both sides of the leaves and on the stems. Soap sprays only work when wet, so they will need to be reapplied every 4-7 days or until you notice that populations have decreased. After a few applications, if rain hasn't done this for you, spray the plants with plain water to rinse off any soapy residue.
- Oil Spray: Mix 1 cup of vegetable oil with 1 tablespoon of mild liquid soap. Add 2-8 teaspoons of this mixture to 1 quart of water and spray your plants as above. The oil in this spray smothers the insects so it is effective on aphids, thrips, mites, and scale.
- Tomato Leaves Insecticide: The leaves of tomatoes contain solanine and tomatine and can be used as an insecticide. Soak 2 cups of fresh leaves in 1 quart of water overnight. Strain and spray. It kills aphids and many types of chewing insects, but also attracts beneficials. Don't use it on other nightshades like eggplants, peppers, or potatoes because it could spread disease from plant to plant.
- Garlic Repellent Spray: Despite all you've read, garlic acts as more of a repellent than a killer. Puree 2 bulbs of garlic with 1 cup of water and let sit overnight. Strain the liquid into a quart jar, add 1/2 cup vegetable oil, 1 teaspoon liquid soap, and fill the jar the rest of the way with water. Put one cup in a 1 quart sprayer, fill with water and apply to your affected plants. It is good for repelling aphids, cabbage worms, leaf hoppers, squash bugs, and whiteflies.
- Hot Pepper Repellent Spray: Hot pepper is also a good repellent and works on rabbits and deer as well as many insects. Mix 1 tablespoon dried chile powder, 1 quart of water, and 1 teaspoon of mild soap. Spray full strength on the plants under attack.
If you have lots of hot peppers growing in your garden, you can make a fresh concoction from 1/2 cup chopped peppers pureed in 1 cup of water. Add the puree to 1 quart of water and bring to a boil. Let sit until cool and then strain. Add 1 teaspoon mild soap and spray full strength on plants. You might want to wear gloves when working with this spray and be sure not to get it into your eyes!
Many other plants have been reported to have insecticidal qualities, including hyssop, lettuce leaves, onions, pennyroyal, peppermint, and radish leaves.
There is no one-size fits all when it comes to pest management. At best we can try to maintain a healthy balance of good guys and bad guys and still get some decent produce for us!
Now that we've learned how to minimize insect pests, let's tackle weeds. Here are tips on coping with weeds, including 5 Homemade Herbicides.