In February, your vines received eight to twelve inches of rain, depending on your location. The deluge was welcome but not even close to enough rain to say we are out of the woods. You can't put your grapevines on autopilot as you might do in wet years. You need a plan.
A smart draught plan starts with pruning, to adjust the crop size to match available water. In prior years, you might have left three buds per vine. This year, two would be wiser. If you didn't do this when you pruned, it's not too late. You can thin after flowering and fruit set.
You may have heard people talk about dry farming—growing grapes without irrigation—but that's a decision to make when you plant your vineyard, not as a response to drought. To dry farm, you need sufficient ground water and a rootstock that will send roots deep enough to reach it. Even dry-farmed Napa Valley vineyards may need irrigation this year as we haven't had enough rain to maintain ground water levels.
Grapevines are relatively drought tolerant, but insufficient water at crucial stages can compromise vine growth, fruit yield and quality. In the period between budbreak and flowering, avoiding water stress is critical. Vines use the water for root growth, establishing the canopy and determining the yield for this year and the next. Water stress between flowering and fruit set can result in poor fruit set, aborted fruit or smaller berries, all of which reduce yield. After fruit set, grapevines can tolerate moderate water deficits.
Before your first irrigation, make sure your system has no leaks andis operating efficiently. Irrigating at night will reduce evaporation loss by up to 10 percent.
Before irrigating,analyze the water content of your soil. Dig a few holes as deep as the longest roots. If the soil at the bottom of the hole is dry, you need to irrigate. If the soil is moist at the bottom, you don't.
Instead of growing a cover crop that takes water out of the soil, use mulch and compost to improve water retention. Control weeds that compete with vines for water. If you have dead or unproductive vines, don't replace them this year. Young vines require more water than established vines, so delay replanting until you know you can meet the new vines' water needs.
Be stingy with nitrogen fertilizer as nitrogen favors shoot growth over root growth, making vines more susceptible tolate-season drought. Monitor canopy size, limiting it to what's needed to ripen the crop.
Last but not least, thin fruit to reduce vine stress. Better to sacrifice some or all of the crop rather than permanently damage the grapevine.
Tomato Plant Sale: Napa County Master Gardeners will hold their second annual “Tomato Plant Sale and Education Day” on Saturday, April 19, in the South Oxbow parking lot on First Street in Napa. The sale will be held from 9:00 a.m. until sold out. All the seedlings have been started from seed and grown by Napa County Master Gardeners. More than 50 varieties of heirloom and hybrid tomato plants will be available. Master Gardeners will staff information tables on tomato support structures, common tomato pests and diseases, composting, good bug/bad bug displays and a mobile help desk. For a list of available tomato varieties, visit http://ucanr.org/ucmgnapa or call the Help Desk (hours below).
Workshop: Napa County Master Gardeners will conduct a workshop on “The Small Home Vineyard” on Saturday, March 29, from 9:30 am to 11:30 am, and from 12:30 pm to 2:30 pm. at the Yountville Community Center, 6516 Washington Street, Yountville. The morning session will focus on bud break to harvest. Learn the basics of managing a small vineyard including grape physiology, canopy management, vine nutrition, fertilization, irrigation and cover crop. The afternoon session will focus on identifying and managing the most common vineyard pests, especially powdery mildew. To register,call the Parks & Recreation Department at 707-944-8712 or visit its web site.
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.
Napa County Master Gardeners welcome the public to visit their demonstration garden at Connolly Ranch on Thursdays, from 10:00 a.m. until noon, except the last Thursday of the month. Connolly Ranch is at 3141 Browns Valley Road at Thompson Avenue in Napa. Enter on Thompson Avenue.