In our climate, fruit trees do need to be watered periodically to stay healthy. A fruit tree's water needs depend on its size, day length and the weather (air temperature, humidity and wind). Under-watering will reduce fruit size and tree growth. With extreme water stress, fruit can sunburn and may shrivel and drop, and the tree may lose its leaves.
Can your fruit trees survive with less water? Yes, they can. In a year with normal rainfall, the soil at the beginning of May is holding as much water as it can. Ideally, you would observe the surrounding hills and start watering when the grass turns brown—a sign that the top six inches or so of soil have dried out. At that point, young trees need to be watered every 10 days to 2 weeks. Established trees only need water every three to four weeks from June through August. This infrequent watering encourages deeper roots, which makes more water available to the tree.
Trees that are one to two years old need just one to two gallons of water per day (applied 15 to 30 gallons at a time). A mature tree can use 50 gallons on a hot summer day. It might need 1,000 gallons every four weeks to replenish the water it takes out of the soil.
Make sure you water slowly enough so that all of the water is absorbed. Younger trees are more susceptible to water stress than established trees. And although you may have heard that citrus trees are drought resistant, they have shallow roots and are actually among the least drought-resistant fruit trees.
So what actions should you take in a drought year?
Water early. In a drought year, the root zone will dry out earlier so you have to start watering earlier. Adequate irrigation early in the season is more important than water later. Trees grow more slowly later in the season, and most trees will have already borne fruit. They may lose their leaves and set few flower buds, but they will survive. In extreme drought, deep watering once or twice in the spring and early summer will likely keep trees alive. However, these trees may not bear fruit.
Mulch your soil. Keep soil moisture from evaporating by applying a generous layer of mulch. Mulching also minimizes weeds that compete with your trees for water. Organic mulch will increase soil fertility and the soil's ability to hold water. Apply mulch to moist soil. If your garden has already dried out quite a bit, water first, then mulch.
Keep your trees small. The smaller the tree, the less water it will need. Home gardeners rarely need all the fruit that a mature standard or semi-dwarf tree produces. Smaller trees are also easier to manage. Thin stone fruits, apples and pears when they have the diameter of a quarter, keeping only about half as many fruits as you normally would. Fewer fruits require less water, and you have a better chance of getting good quality.
Prune hard. During the dormant season, cut back your fruit trees by about one-third. Then prune during the growing season to minimize growth. The goal is to limit the number of leaves the tree is trying to support. You will sacrifice fruit, but your tree will survive on less water. When you prune, paint the newly exposed limbs and trunk area with a mix of equal parts light-colored interior latex paint and water.
Water the right trees. Among common fruit and nut trees, almonds, figs and olives are the most drought-tolerant. Nectarines, peaches and citrus are the least tolerant.
Grow healthy soil. Keep adding amendments. The more organic matter in your soil, the more water it will hold. Healthy soil holds up to five times as much water as depleted soil.
Workshop: Napa County Master Gardeners will hold a workshop on “Let's Talk Rose Care for Spring and Early Summer” on Saturday, May 23, from 10 a.m. to noon. Join in the discussion about spring and early summer rose care, issues and solutions. We will talk about integrated management for common pests and diseases and how to keep roses healthy even during our current drought and water restrictions. Location: University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Online registration (credit card only)
Mail-in registration (cash or check only)
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners ( http://ucanr.org/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.