Backyard grapevines are not water hogs

Question: “We are thinking about planting a half-acre to an acre of wine grapes on our property. Given our drought, is there a way to plant and maintain a residential vineyard and conserve water at the same time?”

And a related question: I have a small home vineyard in my backyard that produces lovely wine grapes. How can I tell if I’m giving them too much water? Can I dry farm them?

Answer: With our ongoing drought conditions in spite of the rain, your concerns about water use are justified. The good news is grapevines use less water than fruit trees and most landscape plants. They also can provide a fire break to protect property against wildfires when properly watered and kept weed-free. Watering requirements vary depending on the weather, soil conditions, topography and the rooting depth of the vines. In general, a good starting estimate is 4 gallons of water per vine per week.

Drip irrigation is the best way to deliver precise amounts of water to each vine without wasting water on the surrounding soil. And while mulching is not practical for commercial growers, it works in the backyard vineyard. Lay down weed cloth or cardboard first, then cover that with wood chips, bark or straw to control weed growth and minimize soil moisture loss.

An inexpensive soil-moisture meter can help you determine when to start watering, the minimum amount of water give vines and how often to water. Grapes don’t need water during the winter, their dormant season. Start watering when the soil begins to dry, in late spring or early summer. In general, you can limit water until you see the first signs of leaf wilting or raisin development, but be careful not to overstress the vines.

Recently, there has been renewed interest in dry farming, although it’s not a new practice. You often can see dry farming in vineyards with old vines. Successful dry farming requires soil moisture within access of the grapevine roots. The level of groundwater tends to be deeper on hillsides, while on valley floors and locations close to streams, even seasonal streams, groundwater is closer to the soil surface.

You need to train vines to be dry farmed. Water young plants deeply but infrequently to force the roots down to the available ground water. Once the vine develops the deep roots, you can reduce or eliminate watering. One caution: When dry farming, have a functioning drip system in place for days of hot, dry conditions, when leaves start to wilt and fruit begins to raisin. A dose of deep watering may be necessary to save the grape crop.

If the groundwater table is high enough, you can convert an established vineyard to dry farming. Begin by deeply watering the vines to encourage the roots to access the groundwater. Over time, increase the water depth while decreasing the irrigation frequency.

For more information, see:

Growing Grapes in Your Backyard: bit.ly/3EsUwF9

How and when do I irrigate: bit.ly/32uAP2K

Q: Every winter, all the leaves on my lemon tree turn yellow and the plant looks unhealthy. How should I treat this problem?

A: Yellow leaves, also known as chlorosis, can be caused by a variety of factors, but uniform yellowing of citrus leaves in winter often indicates nitrogen deficiency, over-watering or both.

Too little nitrogen is the most common mineral deficiency in citrus. Unfavorable soil conditions, including soils that are too wet or too cold, inhibit nitrogen uptake by the plant’s roots. With the arrival of warmer temperatures in the spring, nitrogen deficiencies in the plant subside as the soil drains and nitrogen becomes available. That’s when the leaves should green up again.

Nitrogen is a mobile nutrient, meaning it moves throughout the plant to where it’s most needed. For example, when your lemon is flowering and growing new fruits, plant nitrogen supplies are relocated to the reproductive regions of the plant and away from the leaves, which respond by yellowing.

Citrus prefer well-drained soils and regular watering. The best way to protect citrus from wet and cold conditions in winter is through good cultural practices. Protect the root zone from seasonal temperature fluctuations by mulching with a thick layer of aged compost. The nutrients in this surface layer of compost gradually find their way into the root zone and provide a balanced nutrient supply.

If winter temperatures drop below freezing, cover citrus with a frost blanket. An alternative method is to string old-style holiday lights through the branches; they usually provide enough heat to keep the plant from freezing.

Because citrus need a regular supply of nutrients, it may be beneficial to apply an organic fertilizer formulated for citrus in February and then two more times, four to six weeks apart.

For more information on growing citrus, see the UC California Backyard Orchard website: bit.ly/3pNvQDq.

January in the garden

• Prune roses anytime between New Year’s and Valentine’s Day. Be careful not to compact the soil around the plants with your feet when you prune. Prune hard, down to three to four young vigorous canes per plant.

• Keep an eye on weather forecasts. When frost is expected, protect frost-tender plants such as citrus, hibiscus and bougainvillea. Cover plants with sheets, lightweight blankets or burlap. A strand of incandescent holiday lights in a citrus tree is often enough to protect the plant from frost. Move container-grown succulents, citrus or other vulnerable plants under the canopy of a leafy tree or the eaves of an overhanging roof to shelter them for the duration of winter.

• You can start seeds indoors now for cool-season leafy vegetables, like lettuce, collard greens, kale, Swiss chard and spinach, and for brassica family of crops, like broccoli, spring cabbage and cauliflower. For information on when to plant your starts, see our useful guide to year-round food gardening in Sonoma County: bit.ly/3ilxJlI.

• Plant bare-root asparagus crowns, rhubarb rhizomes and bulb onions.

• Clean, oil and store tools such as shovels, hoes and pruners. Apply light machine oil to metal parts to prevent rust. While you are cleaning, consider spray painting the handles of the tools a fun color to keep your tools separate from any you happen to borrow or lend out. This also makes them easier to find in the yard.

Contributors to this week’s column were Janet Bair, Patricia Decker, Karen Felker, Dennis Przybycien, Laura Southworth and Debbie Westrick. Send your gardening questions to scmgpd@gmail.com. The UC Master Gardener Program of Sonoma County (sonomamg.ucanr.edu) provides environmentally sustainable, science-based horticultural information to Sonoma County home gardeners. The Master Gardeners will answer in the newspaper only questions selected for this column. Other questions may be directed to their Information Desk: 707-565-2608 or mgsonoma@ucanr.edu.