By Diane Hyde, OSU Extension Master Gardener Volunteer
Summers are getting hotter and drier while water is getting more expensive. Some vegetables can produce acceptable yields successfully with no supplemental irrigation with some careful planning. Not all vegtables are suitable for dry gardening, and not all locations will support gardens without water. Dry farming has been done for millennia, and knowledge of the practice has been passed on in a few farming families and cultures.
Oregon State University Extension Dry Farming Project has focused on management strategies to grow with little or no irrigation. Yields may be 25% to 50% less than irrigated crops because plants are spaced out farther apart. Each plant can still have good yield, so a family dry garden might take more space to provide as much produce. Produce grown without irrigation has often been judged to be more better in color, texture and sweetness in taste comparisons.
Successful dry gardening requires soil that will retain spring rain water. Clay soils and organic humus will hold seasonal moisture, but if the underlying ground has rock that drains well then water will not be available for the summer. Four feet of moisture-retentive soil is recommended. Shallow, rocky or sandy soils may not hold enough water for decent crop yields. The climate should have a wet period, like ours, that provides lots of moisture prior to the dry period. The dry garden area should have no competing trees, shrubs or turf sucking up the water before the vegetables can get it.
Sloped land holds less water than flat land. South-facing gardens lose more water to evaporation than north-facing gardens. A windy garden site will lose water from plant leaf evapotranspiration. A site that grows good weeds or healthy blackberries with no irrigation may be a good place to transform into a dry garden.
To dry garden in summer, plant as early in Spring as possible to take advantage of seasonal rain. Soil in our area can often be prepared as early as February to April, but frost dates and soil temperatures limit which veg will grow that early. Seeds need to be planted in wet soil, deeper that the seed packet recommends if the surface has dried. Pre-soaking seeds 24 hours before planting helps them germinate and establish more quickly. Transplants may need to have all but the top leaves removed and the stems buried as deep as possible. Mudding in the plants at planting, filling the hole with water, will get the roots started well so they can deal with no more irrigation.
Roots will reach deeper and wider in a dry garden, so more space per plant will be required, probably at least twice the space recommended on the seed packet. Because there is less water applied to dissolve ground minerals, lime applied to the soil before planting helps prevent blossom end rot in tomatoes, squashes, peppers and other veg that require more calcium. Mulches applied deeply after the plants are established will retain more moisture and keep the soil cooler.
Indeterminate (vine) tomatoes, especially earlier-producing small cherry varieties, produce flavorful fruit in a dry garden if they are started well. Peppers, potatoes, winter squash, zucchini, melons, dry beans and corn are commonly dry-farmed. Beets, carrots, chard, kale, leeks, rutabagas will grow without irrigation, but will do better with occasional water. Fall-planted garlic, fava beans, root crops and leafy greens establish in the rainy season and mature without irrigation in early summer. Fall-planted broccoli, kale and other cool-season crops can grow through winter but bolt and flower quickly when warmer weather arrives. Spring-planted onions, celery, radishes and greens require irrigation to be productive. Choosing varieties with shorter growing periods listed on the seed packets means they might complete their growing cycle before the water dries up.
For more information about dry vegetable gardening and a list of resources visit http://center for small farems.oregonstate.edu/dry farm.
Extension publication “Intro to Dry Farming Organic Vegetables” is available for free download at catalog.extension.oregonstate.edu/EM9229.