Water is an essential ingredient in all plant growth, for almost every botanical process takes place inits presence. Water is necessary in plants’ food-manufacturing process (photosynthesis), is the main constituent of living cells, and abounds in young plant tissues. It keeps stems and leaves stiff. And water is the main ingredient in most of the vegetables we eat, comprising, for example, 91 percent of asparagus, 87 percent of beets, 95 percent of cucumbers, and 94 percent of tomatoes.
These facts might suggest that all you have to do in order to grow sumptuous vegetables is pour on the water. Unfortunately, Mother Nature doesn’t work that way. Too much water is just as harmful as too little.
Critical Watering Periods
Vegetables need a constant water supply for best growth. Inadequate water, however, affects vegetable quality most during the following periods.
asparagus spear development
beans pollination/pod development
broccoli head development
cabbage head development
carrots root enlargement
cauliflower head development
corn tassel/ear development
cucumbers flower/fruit development
eggplant flower/fruit development
lettuce head development
melons flower/fruit development
onions bulb enlargement
pumpkins flower/fruit development
squash flower/fruit development
tomatoes flower/fruit development
How Much Water?
To keep your vegetables growing at their fastest rate, water until your particular soil type is filled to field capacity in the main root zone (about 1 foot deep for most vegetables, about 2 feet deep for corn, tomatoes, and a few other large vegetables); don’t water again until most of the available water has been used.
The amount of water your plants use depends on temperature, wind, rainfall, and individual needs. The amount of water your soil holds depends on its texture. Sandy soil holds less water than clay, yet clay holds water so tightly that some of it is unavailable for plant use. Loam makes adequate amounts of water readily available to your vegetables.
If you know what kind of soil you have, you can estimate roughly when your soil is saturated, or has reached field capacity. If you have loamy soil, approximately 1 inch of water will saturate the first foot. To help with gauging this, place a large transparent measuring cup in the garden. When a inch of water has accumulated in the cup, the top foot of your garden has all the water it can hold.
Soil Water-Holding Capacity
(Inches of water needed per foot of soil depth)
Water Use Guide
(inches of soil water used per day in a vegetable garden)
Season 80 Degrees F. and Above Below 80 Degrees F.
Summer .25–.35 .15–.2
Spring/Fall .1–.2 .1–.15
A fail-safe watering method that maintains the correct degree of soil moisture is to water deeply for two to four hours, and then wait until the soil dries out to a depth of 4-8 inches before watering again. You can use a trowel to check.
How to Water
Home gardeners generally water overhead or use some sort of drip system. I urge you to install a drip system to conserve water, but many continue to water both ways. The chief advantage of overhead watering is that it’s easy. The principal disadvantages are that a great deal of water is lost through evaporation and that it makes the garden more susceptible to disease.
In general, exercise some prudence whenever you overhead water. Remember to water early in the morning to enable the leaves to dry off quickly; lingering moisture can create a mildew problem. In addition, the leaves of some plants, such as squash, may burn if the plants are watered during the heat of the day. Water tomatoes overhead only until the fruit begins to ripen; then, to keep the fruit from cracking, water on the ground until you have harvested the plant.
Drip irrigation is the frequent, slow release of water into the soil through small mechanical devices called emitters. The system consists of three main parts: basic controls, a main line or lines, and emitters with small extension tubes.
Drip systems are available in kit form or as individual components at nurseries and plumbing supply stores. They are usually easy to install in average size gardens.
Drip irrigation is by far the most efficient watering method for vegetable gardens. Only a key area of soil is watered, little or no water is lost to evaporation and surface runoff, and there is no sprinkler overshoot. As water becomes more expensive and water conservation even more important, many vegetable gardeners will use this method exclusively.
Mulching Means Moisture
Gardeners can also use mulch to ensure adequate soil moisture for vegetable plants. A mulch is any material spread on the garden bed that shades the ground completely, reduces soil evaporation, and helps retain moisture. Many organic materials will make a good mulch; you can try wood chips, sawdust, grass clippings, horse manure, or compost.
Place organic mulches around your plants’ stems, and cover the ground completely. Since organic material cools the soil, mulch in late spring after the soil temperature has warmed to at least 65 degrees F. The best time to spread an organic mulch is immediately after a rain, as it keeps the moisture in the soil for an extended period of time.
Water has such importance in the garden that it is worth repeating the fail-safe approach: Water deeply for two to four hours, and then don’t water again until the soil dries to a depth of 4-8 inches. Test with a trowel. If you follow this rule and garden in well-drained soil, you will probably be able to deal with conditions ranging from drought to several days of rain.