in the soil, in the tissues of the plants, and deep in the ground.
Organic matter is the key to retaining moisture within the soil. It holds water within particles of humus, yet allows life-giving oxygen which watering often excludes. Mulch is another way to hold water in the soil, by preventing evaporation. In hot places with cool nights, it is well worth trying a mulch of stones. Fist-sized rocks shade the soil, seal it from evaporation, and radiate the day’s heat at night, helping crops to ripen. They can also add an appreciable amount of moisture to the soil from the dew that condenses on them.
To retain water in the plants, protect them from wind—a dry wind can double their need for water. Light fencing like reed, bamboo, or even cloth or dead branches will work. So will a hedge or belt of fruit trees to the windward side of your garden. If you live in a place with intense summer heat, your plants will probably appreciate some shelter from midday sun. Leafy crops should be sited on the east side of taller crops or buildings so they get morning sun only. Even peppers and tomatoes will stop growing and setting fruit if the temperatures are much above 90°. You can use shadecloth, or position tall crops like corn so that your vegetables get an hour or two of shade sometime between noon and 4. Trees that cast a light shade are helpful, and if they are nitrogen fixers, they won’t rob your vegetables of nutrients. Honey locust and mesquite work well for this.
Plant roots go deep if they can, and deep water is the key to self-sustaining landscapes. Earthworks like swales, hugelkulture, or sunken beds will really pay off here. To learn more about them, see the permaculture resources below. To make a sunken bed, don’t take the topsoil off to make a low spot. Save the topsoil to one side, remove a layer of subsoil, and then replace your topsoil, well amended with compost. Or build a dike or berm around your beds to retain water.
If you live in a summer-dry, winter-wet climate, try to use that water when you have it by keeping your garden full of growing crops during the winter rains. Start your spring crops early while there is moisture and the weather is gentle. Row covers hoophouses, or cold frames can keep your crops growing while there is plenty of free water in the soil.
Irrigation should be done in the evening or early morning to prevent evaporation. Keep water off of plant leaves.
Resources: Growing Food in a Hotter, Dryer Land, by Gary Nabhan Rainwater Harvesting by Brad Lancaster Gaia’s Garden by Toby Hemenway Desert or Paradise by Sepp Holtzer The Resilient Gardener by Carol Deppe How to Grow More Vegetables by John Jeavons