Which is worse, the insects helping themselves to your garden or the outrageous expense of the remedy from the boutique nursery in town? Thankfully, it's not a choice you have to make, as many simple, inexpensive, organic formulas do a good job of killing or repelling bugs in the vegetable patch.
Dormant Oil Spray
If your trees and shrubs play host to the same pests year after year, consider making the effort to make this oil-soap spray that is applied while the plants are dormant. The film kills overwintering eggs and larvae, preventing their emergence in the spring.
To make a concentrate, combine a gallon of oil (mineral, lemon or fish) with a lb. of olive-oil based soap and 1/2 gallon of water into a large pot. Heat on medium until all is one mixed, cloudy suspension.
Immediately take one part of this mix, add to 20 or so parts of water, and spray it on dormant foliage, preferably in the very early spring, right before buds swell, and at a temperature above freezing. Make sure every part of the bark gets a good coating.
Nicotine is toxic to bugs and people. Crush four or five cups of fresh tobacco or two cups of dried tobacco leaves into about five quarts of water and let steep for a full day. Strain, and add another quart of water combined with 1 tsp. of liquid non-detergent soap. Keep adding water until the color is a light brown, like weak tea. To use, either spray it on plants or pour it around roots to foil attack from the ground up.
Caveats: Do not use on roses, which will turn black. Because of the danger of tobacco mosaic infection, do not use on tomatoes that have not yet flowered. Keep this spray well out of the reach of children or curious pets. Do not eat whatever has been sprayed for a few days, and wash produce well before consuming.
Soap disrupts normal cell respiration in most soft-bodied bugs like aphids, mealy bugs, spider mites and young scales, paralyzing and killing them, yet isn't toxic to humans and pets. Dissolve 1tsp. of pure bar soap shavings in 1/8 cup boiling water, then add 7/8 cup of water. (Hard water will not work well for this.) Apply as a spray.
Caveat: Soap can burn plants, especially on a very hot day. Some gardening experts recommend that you rinse off the soap about an hour after application, since it won't be effective after it dries anyway. Keeping the concentration to about 1 to 2 percent of the solution will still be effective, but will be much safer for plants.
Potato Starch Spray
Originally found to gum up cabbage moths, killing them once it dries hard, potato starch has also proven effective against the other usual suspects: aphids, thrips, spider mites, etc. Soak a cup of potato starch in a gallon of water for a few minutes, then add about 1/2 tsp. liquid non-detergent soap. Apply as a spray.
Caveat: This stuff is flaky and messy-looking, but can be hosed off a day or two after application.
Several garden plants are natural repellents for many kinds of bugs. Examples include rhubarb leaves, tomato leaves, hot peppers and garlic. Mash a couple of cups of any of these three, and allow them to steep in a quart or so of water for a full day. Strain, add 1 tsp. of liquid non-detergent soap and apply as a spray.
The tomato and rhubarb combinations have been shown to actually attract some beneficials, unlike many of these sprays that take out friend and foe alike, so they may help bring your garden into better ecological balance. The volatile allicin from garlic just smells, which is a deterrent to almost all bugs and animal pests.
Caveats: Tomato and rhubarb leaves contain alkaloids, which are toxic to humans, too. Wear gloves when handling the peppers and the pepper spray bottle, as it could burn your skin. Keep these out of the reach of children or pets.