This homemade spray is effective on whiteflies and aphids, two pests which may show up if you're starting seedlings indoors:
Put into a pint mason jar or non-metal pan:
Pour 1 cup boiling water over herbs, cover, and let steep for 2 hours. Strain out herbs. Add 1/4 cup biodegradable dish soap. Pour into bottle and cork or cap.
This is a concentrate: dilute 1/4 cup concentrate with 3/4 cup water to use. Fill spray bottle. Spray bug-infested plants, especially on growing tips and on undersides of leaves. Next day, mist with plain water. Repeat one week later. I've found this spray works better than Safer Soap, doesn't hurt the plants, and gives me a grand excuse to say that my non-Calendula marigolds are blooming in my garden for more than just a pretty.
Leda