Extreme temperatures can turn a healthy vegetable garden into a limp wasteland in less than a day without adequate water. Even if the plants survive the heat, insufficient water can affect the flavor, make plants vulnerable to disease and cause fruits to crack. When the mercury soars, the usual recommendation of 1 inch of water a week is not likely to be enough, and you might find that daily watering is necessary on the hottest days. But how much water is enough? For the right answer, you need to consider several factors, such as soil type, wind, depth of roots and the effectiveness of your watering methods.
Not all soils are created equal. Loamy soil is considered the ideal because its particles are big enough to allow for good drainage but small enough that water won't drain through too quickly. But not everyone is lucky enough to have good loam. If you have clay soil, the small particles bind together to hold water longer--sometimes long enough to drown tender roots. Sandy soil, on the other hand, has large particles that allow water to filter through quickly, which means you'll need to water more often, especially in periods of high heat.
While heat can be damaging enough, heat and wind together can be deadly for your plants. Dry winds accelerate the speed with which plants lose moisture and wilt. Large-leaved plants like squash (Cucurbita spp.) can be particularly vulnerable to moisture loss from winds since they have larger leaf surfaces that release moisture. If high temperatures are accompanied by winds, it may help to erect a wind break around tender plants in addition to providing more water.
Depth of Roots
However much you water, it only helps plants if the water reaches the roots, and different plants have root systems of different depths. Many vegetable plants have roots that go 6 to 12 inches deep, but some, like tomatoes (Lycopersicum esculentum), squash, corn (Zea mays) or melon (Cucumis spp.), or perennial vegetables such as asparagus (Asparagus officinal) and rhubarb (Rheum rhabarbarum) can reach down 24 inches or more. After you water, insert a metal rod into the ground until you feel resistance, indicating that the rod has hit dry soil. The depth of the rod into the soil will tell you how deeply the water has penetrated.
Efficient watering techniques become even more essential in periods of extreme heat. To make the most of your irrigation, water early in the morning hours to minimize evaporation, use a drip irrigation system or soaker hoses to deliver the water directly to the roots and apply a 3- to 4-inch layer of mulch to help prevent the soil from drying out too fast. Don't forget to monitor container plants closely since they dry out more quickly than those planted in the ground. Take all these factors into consideration, and you'll be able to determine how often to water your vegetable garden to help it thrive in the heat.