Most vegetable crops require one inch or more of water each week during the growing season. This is the equivalent of about ¾ of a gallon of water. In hot, dry conditions vegetables may demand more water.
Insufficient or uneven water can cause plants to grow in fits and starts and may result in wilting, blossom drop, leaf drop, malformed fruits, and sometimes death of the plant.
Evenly moist soil can slightly lower the soil temperature and increase humidity around crops. This will help alleviate plant stress in hot weather.
Hot weather watering solutions:
• Group plants with similar water needs. Plant crops with similar watering needs close together. Group plants into “hydrozones”–groups of plants with similar water, soil, and exposure needs. This will allow for the most efficient application of water. Deep rooted crops such as carrots and beets (roots to 5 or more feet) should be planted in one section of the garden. Plant medium-rooted crops such as tomatoes and corn (roots to 4 feet and sometimes less) in another.
• Water according to need. Shallow rooted crops, new transplants, and seeds require more frequent watering than established crops with deeper roots. Soil moisture evaporates more quickly from the top two to four inches of soil than from deeper soil. Plants that are flowering or setting fruit need deep, even watering.
• Furrows and basins. Hand-water plants bordered by furrows or surrounded by basins. Seeds and transplants can be set at the bottom of 6 to 8 inch trenches, rather than on the top or sides of furrows in very hot summer regions. Basins 3 to 6 inches deep can be built around widely spaced crops such as squash, melons, and tomatoes. Use a hose-end bubbler attachment to irrigate.
• Soaker hoses. Use a soaker hose to water crops planted on flat beds. This is the most effective way to water leafy crops and crops intensively planted.
• Drip irrigation. Use a low-volume irrigation system with emitter line for closely spaced plants. Use individual emitters for widely spaced plants. For vegetable gardens in sandy soil, set several 2-gph (gallons per hour) emitters about a foot apart in a row; in loam soil set several 1-gph emitters about 1½ feet apart in a row; in clay soil set several ½-gph emitters about 1½ feet apart in a row; in containers using potting soil set one or more ½- or 1-gph emitters in each container.
• Sunken beds. In arid regions, sunken beds–the opposite of raised beds–can be used to captur rain and irrigation water during the rainy season. During the dry season, crops planted in sunken beds will draw upon the reservoir soil moisture captured during the rainy season. Sunken beds will also protect plants from drying summer winds.
Other watering tips in hot weather:
• Keep an eye on your plants. Know the signs of water and heat stress: wilting foliage and sunburn. If plants are wilting at the end of a hot day there may be no concern. But if plants are wilting at the start of the day, water immediately. If plants show signs of sunburn (leaves with yellow or white spots in the center), place shade cloth over the plants.
• Know the soil in your garden. Examine the soil frequently to know how much water it is retaining. Vegetables grow best in soil that is evenly moist, meaning not too wet and not too dry. Thrust a finger into the soil; if come out dry, the soil needs water; if it comes out glistening wet, the soil is too wet; if it comes out just damp, the water is just right. Sandy soil requires more watering, clay soil less. Add well-aged compost to your garden to keep soil moisture just right.
• Water plants deeply. Irrigate so that the root zone receives water, not just the top few inches. You can push a long wooden dowel into the soil after watering to get a sense of how deeply you’ve watered. The probe will move easily through wet soil and haltingly or not at all through dry soil.
• Avoid runoff. Apply water until it begins to puddle then stop until the water is absorbed; then repeat the cycle so that the water penetrates the growing bed rather than runs off. A drip or low-volume irrigation system will aid in delivering water evenly. Furrows and basins can help stem runoff. Terraces on slopes will slow runoff.
• Adjust the watering schedule as necessary. Water more frequently in hot or droughty weather; water less frequently in cool or cloudy weather. Water in the morning or in the evening when evaporation is lower. Avoid watering in windy conditions.