A modest amount of fertilizer amended into the soil will help ensure the success of your herbs. Organic Compost contains some of the nutrients they will require and combined with a light mulch will help provide a soil composition that allows for aeration and drainage. If you have a clay soil, some sand amended into the garden bed is also advisable.
Adding several inches of organic mulch at the base of plants optimizes moisture retention. Mulch the bed after planting to aid in water retention and weed retardation.
One of the natural elements that all plants require is silica aka silicon. Silicon is proven to enhance drought and heat tolerance in plants. It is for the most part extremely abundant in nature, second only to oxygen. It makes up about 1/4 of the Earths crust. It is a naturally occurring element found in soil. It strengthens the plants cellular walls, improves the plants tissue strength and ability to withstand adverse climatic conditions. There are several ways to ammend silicon into your garden bed. See - Silicon for Drought Gardening
Drip irrigation uses 30 - 50% less water than conventional watering methods, and uses it more effectively. Drip systems will also inhibit the encroachment of competing weeds as the water is delivered to precise locales aimed at where your plant can utilize it. See Drip Irrigation for Drought Gardening
Herbs that Resist Drought
Oregano is one of the most commonly used herbs. It can be grown throughout most of North America but its drought hardiness varies from variety to variety. It does best in full sun, but will tolerate partial shade. In hotter arid climates partial shade is best.
is a close relative of Oregano and has pretty much the same qualities.
Chives - both Onion Chives and Garlic Chives work well in a low moisture gardening scenario.
Parsley is an option for a drought garden. Not as tolerant as Oregano but still workable. It is a biennial that can also be grown as an annual.
Sage is drought tolerant. It is a low shrub sometimes wider than it is tall commonly grown in herb gardens. It has a light green foliage with delicate blooms and is related to evergreens.
is an extremely hardy perennial. It's pretty hard to kill, no matter how much you neglect it. Mulch your plants to retain enough moisture near the roots during the dog days of summer and to provide winter insulation.
Thyme has very small flowers and leaves. Depending on the variety, the flowers can range from white to a deep magenta and all shades in between. Thyme thrives under full sun and a dry, well drained soil with a pH of about 7.0.
Lavender is a flowering plant used as an herb, a medicinal and a fragrance as it gives off a euphoric aroma. It is also said to repel mosquitoes and best of all will tolerate very arid conditions.
Lemon Balm ' another mint family member that is somewhat drough tolerant as are nealry all mint plants.
Lovage 'Levisticum officinale, or lovage, has a strong sweet to salty celery-like flavor.
Echinacea / American Purple Cone Flower ' is a popular herb proven to bolster the immune system. It is also an aesthetically pleasing perennial garden flower. It makes delicious eye candy for any landscape scenario. It has a very long tap root which helps it tolerat arid conditions.
Fennel also has a long tap root which makes it drought tolerant, it is hardy to zone 5. It serves not only as a spice / herb, but also a vegetable.
Artemisia, Catmint, Germander, yarrow, some varieties of horehound are other herbs that fare well under adverse hot arid climates.
Companion Planting Drought Resistant Tomatoes
Mychorizae Beneficial Fungus For Garden Plants Drought Resistant Tomatoes