Vegetables need water to grow quickly, tender, and tasty. Keep the soil evenly moist throughout the growing season—that means not too wet and not too dry. If the soil dries out, vegetables can become bitter-tasting and woody. If the soil is too wet, vegetable roots can become starved for oxygen and plants can die.
Water vegetables often enough to keep the soil around roots moist, but not soaking wet. As a general rule of thumb, water maturing and mature vegetables to at least 18 inches (45cm) deep. Water transplants often enough to keep leaves from wilting—so that the soil is moist from 2 to 6 inches (5-15cm) deep. Water newly planted seeds to keep the soil surface moist.
There is no secret formula for how often you should water vegetables, but as a guide maturing crops need water every 3 to 7 days during the summer, every 5 to 10 days during spring and fall, and every 7 to 14 days during the winter.
Vegetable Watering Tips
• Keep roots moist. Water vegetables often enough to keep roots moist, but not soaking wet. Roots grow out to the plant’s drip line—the imaginary line made by rain falling off the tips of the broadest spreading branches and leaves. Most vegetable roots grow 18 to 24 inches (45-60cm) deep, some deeper. Because plants use soil moisture to take up water and food, it is important that the deepest and widest spreading roots stay moist.
As vegetables mature a shallow saucer-shaped basin at the base of each plant will ensure water is soaking down to roots, especially in dry weather. Push up soil from outside the drip line to form a circle around the stem of each plant. Don’t dig or scrape from inside the drip line, shallow roots might be exposed or damaged.
Fill the basin with water and let it soak down into the soil; then add more water allowing it to soak in as well. Do this until the water reaches the root zone.
• Measuring water depth. Make a moisture probe from a simple metal rod ½-inch (1.2cm) diameter and 3 feet (.9m) long with file marks at 1 foot and 2 feet. Most vegetable roots grow to a depth of 18 to 24 inches (.4-.6m). A metal rod will easily slide through moist soil; dry and rocky soil will be problematic. If your moisture probe comes away from the soil easily, you can measure the soil moisture depth.
• Water deeply. Deep watering will carry nutrients down to the roots. Soil nutrients in aged compost and dry and wet fertilizers will reach plant roots with each watering. Add fertilizers around plants midway through a deep watering session. This will prepare the soil to receive the fertilizer and send it down to the roots as you continue watering. Deep watering will also wash soil salts that damage tender plant roots deep into the soil; a shallow watering often draws salts to the soil surface. (White or gray deposits on the soil surface are commonly soil salts.)
• Water early in the day. Morning is the best time of day to water vegetables. Morning water prepares plants for the stress of midday heat and allows them to grow uninterrupted. Watering wilted plants in the evening will restore wilted plants but it does no facilitate uninterrupted, continuous growth required for the best yield. Deep watering will sustain vegetables for two or three days or more depending upon the daytime temperature. Erratic watering can stunt plant growth.
• Wilting plants. Plants that need water will droop and wilt. But plants that have been overwatered will droop too. When the soil is water-saturated oxygen will not reach roots and plants can drown. When a plant is wilted and you are not sure if it is under or over-watered, use your soil probe to check the soil moisture. Don’t assume that a wilting plant is short of water. Check the soil probe.
• Water when it is windy. Winds are drying drawing moisture from plant leaves and hastening soil moisture evaporation. When windy weather comes or is forecast, make sure vegetables are deeply watered.
• Water when it rains. Don’t assume a summer rain will soak down to plant roots. When the weather has been dry and rain follows rainwater is likely to run off sun crusted and hardened soil surface. Keep vegetable garden beds lightly cultivated so that rainwater easily soaks into the soil. And water after a rain if plants wilt and your soil probe says the rain did not reach the root zone. Summer humidity stimulates plant growth. If the storms pass by and don’t drop rain, make sure your crops still get the water they need.
• Don’t spray or sprinkle plants. Avoid overhead sprinkler or spray watering; some water is lost to evaporation immediately and much water falls away from plants where it is not needed. Water that drops and sits on leaves during sunny weather can result in leaf burn. Moisture that sits on leaves in cloudy or cooling weather can attract fungi spores floating through the air. Use drip irrigation, soaker hoses, bubblers, basins around plants to deliver irrigation. Soaker hoses and bubblers can diffuse a stream of water and spread it around plant stems. Drip irrigation delivers water almost directly to plant roots.
• Drip irrigation. Drip irrigation delivers water directly to the root zone; the water will seep slowly from drip emitters into the soil a drop at a time. Almost no water is lost through evaporation or runoff. But be careful that drip emitters don’t water just in one spot. A concentrated drip can result in roots growing in tight balls. Drip irrigation should encourage uniform root growth—roots growing out in all directions. Large plants will need two or three emitters so that the water is delivered across the root zone. Place drip irrigation on top of the soil where it can be easily repaired and changed quickly for successive crops.
• Irrigation timers. Timers for drip systems, soaker hoses, and bubblers operate automatically, at regular intervals—whether the soil is wet or dry and whether plants need water or not. Use a soil probe with any irrigation system to be sure roots are getting the right amount of water. Adjust automatic irrigation timer systems to plant needs and weather. Don’t rely on a timer to get it right all of the time.