Herbs add flavor to food and variety to meal preparation. Some herbs have medicinal qualities. According to Janice Cox, author of "Natural Beauty at Home," peppermint, for example, eases upset stomachs. Scented herbs such as lavender and clary sage are used for essential oil production. Other herbs such as chamomile and lemon balm make tasty teas.
Hardiness isn't as much a concern with leafy herbs. There is no time to maturity to harvest like potatoes, peppers or peas. Herbs don't have to ripen like tomatoes. Harvest leaves as soon as the plant is 4 or 5 inches high. Plant herbs in the early spring as soon as the soil can be worked and after the average date of last frost. Dig up herbs before the first fall frost, pot and bring in the house.
Clip the herbs back to keep them bushy and growing even if you won't be using them immediately. Harvest young leaves. Wash the herbs thoroughly. Put in a blender with a little water and freeze in ice cube trays. Thyme is difficult to remove from the stem. Place the washed stem in the freezer. The frozen leaves will easily break off the stem. Keep herbs harvested and they'll keep producing and growing.
Harvest before the flower buds appear or soon afterward. Flowering herbs are not as full of flavor as before they've bloomed. If they do flower, save the seeds to plant next season. Some herb seeds are spices like dill, coriander, mustard and fennel. Let the herbs go to seed. Pick the flower heads and place in a paper bag. Shake the head in the bag to catch the seeds.
Most herbs originated in the Mediterranean with its dry summers and poor soil. Adding fertilizer and soil amendments aren't as necessary for the herbs to thrive as with flowers and vegetables. If the herbs are green and growing, make sure they have enough water---but don't waste fertilizer on them. If the herbs are yellowing, then see if adding a bit of plant food helps. Leaves that are yellow but with green veins may mean the plant needs iron.
Herbs like mint, oregano and thyme spread through underground runners. Keep the herbs contained in the garden as they have a tendency to take over. Mint is especially troublesome in this respect. Keep it in a terracotta pot that has a coffee filter placed over the drainage hole. Keep herbs in their own beds or pots so no confusion is made over which plants are edible and which aren't.