- Water — that's right, just a thumb over the end of a hose and you have a powerful weapon against aphids and spider mites. You can knock a lot away with just a strong spray of water.
- Dish soap — a great additive to plant sprays, helping your concoctions adhere to leaves and insects. A soap and water solution alone can be effective against aphids and other soft-bodied insects, causing their bodies to break down.
- Citrus — it can repel and also break down soft-bodied insects. Pour boiling water over grated lemon, orange or grapefruit rinds and let it steep overnight (1 pint of water over 1 whole fruit's worth of rind). Strain out the liquid into a spray bottle.
- Vinegar — put a small amount of vinegar and sugar (or just use cider vinegar) in a jar next to your plants and aphids and fruit flies will be attracted, fall in, and drown.
- Hot peppers — they contain capsaicin which causes insects to be 'burned'. Too strong of a concentration, though, and plant leaves can also be burned. Combine 1 quart of water, a squirt of dish soap, and a tablespoon of cayenne pepper.
- Ginger — contains capsaicin, just like hot peppers, and can also be used in the same way to make sprays, mixed with water and dish soap ( and sometimes canola oil) to irritate and smother pests.
- Garlic — contains allicin, which confounds many insects' sensory receptors. You can chop up cloves with water in a blender, strain the bits out and then use this extract in a dilute form.
- Baking soda — has fungicidal qualities. Mix a few tablespoons in a quart of water, and use this as a spray against fungus on plants. Reapply every few days until the fungus is gone.
- Milk — mixed with equal parts water can be applied to tomatos, cucumbers, lettuce and other plants to help control mildew.
- Cinnamon — If you see that your seedlings are being affected by damping off disease, you can sprinkle cinnamon down as a fungicide. Damping off is when fungus proliferates in the damp seedling environment, attacking and killing the young stems and roots.
It is recommended that any sprays, especially ones with hot pepper and garlic or onions, be applied earlier in the morning, before the heat of the day and before the plants' leaf pores open up. Spraying later and during the heat of the day will increase the chance of you burning your plants.
Another good precaution is to try spraying only a test portion of the affected plant and see if it has any adverse effects. If you do notice leaf burn, you should wash the area out with some water.
Straining your mixtures is extremely important for anything going into a spray bottle - any little bits will quickly clog the spray mechanism and make a mess. When you are spraying garlic or hot pepper you definitely want to keep that off your hands as much as possible!
(Re-edited from a post originally published on 5.14.2010 - CM)