Published in the Contra Costa Times on July 19, 2008
Question: I want to grow my own vegetables, but am very concerned about my water bill. How much water do vegetables need?
Answer: You bring up a very important aspect of growing food. The majority of the plants we like to eat need a substantial amount of water delivered on a regular basis. If you are planning on replacing a lawn, the vegetables will need approximately the same amount of water, with the advantage of being able to eat the fruits of your labor.
There are other excellent reasons to grow your own vegetables: flavor, nutrition, freshness, food safety and reducing the carbon footprint of your dinner. If you decide to grow your own, you will want to make the most efficient use of the water you are paying for.
Amend the soil with plenty of compost, as compost helps the soil hold moisture for plant roots.
Consider installing drip or trickle irrigation that applies water directly to the roots, minimizing runoff and evaporative loss. There are many kinds of drip systems available at nurseries and hardware stores.
Keeping the soil surface covered with mulch reduces the evaporative loss and minimizes weeds, which compete with plants for moisture. Newspaper can be used as it breaks down, but it needs to be covered with something heavier, as it tends to blow around. Wood chips or grass clippings can be used to cover paper mulches.
Automatic irrigation systems can be scheduled to start in the early morning hours when evaporative loss is minimized.
Deciding how much to irrigate can be an art in the ever-changing climates found in this area. You want to irrigate when the plants need moisture. If they become water-stressed, it will negatively affect yield. Water when the soil at the 4-inch depth falls apart when you squeeze it, or look for slight wilting on hot afternoons.
Water long enough for the water to penetrate as deeply as the roots, which may mean watering for several hours if you are using drip. Never water so long that you see runoff occurring. Vegetables plants will rot if overwatered.
Choose crops that have deeper root systems such as tomatoes, corn, winter squash, melons and asparagus. Summer squash, carrots, peppers, beans and cucumbers root at an intermediate depth, while potatoes, onions, rutabagas, turnips, radishes, lettuces, celery and cabbage are shallow-rooted, requiring more frequent irrigation.
Plant warm-season crops now and cool-season crops in the fall. For lists of warm- and cool-season crops, call the Master Gardener hotline at 925-646-6586.
Bethallyn Black is director of the Contra Costa Master Gardeners, a program associated with the University of California Cooperative Extension and supported by Contra Costa County. Reach her at bblack@ucdavis.edu, or 925-646-6586. General questions for the Master Gardener should be sent using our Question Form