If you haven't done so already, get out your pruning shears, sharpen them and make sure they are functioning properly. Grapevines need a haircut now to be at their best when bud break occurs.
The purpose of pruning is to remove dead, broken or diseased wood; eliminate older, non-productive or marginally productive wood; and encourage development of new wood for future crops. Pruning opens the canopy to sunlight, air and spray penetration. It also makes future pruning, thinning and harvesting easier and keeps the plant to a desired size.
Many home grape growers prune too lightly. As a rule of thumb, you need to remove 90 percent of the wood produced the previous season. Prune mature vines yearly to remove all growth except one-year-old fruiting canes and renewal spurs.
Grapes are produced from buds that grow into shoots on one-year old canes. To fruit well, these canes need light during the growing season. Canes should be thicker than a pencil and as close to the trunk as possible.
Grapevines may be cane pruned or spur pruned. Most table grapes produce the highest yield of good-quality fruit when cane pruned.
To cane prune, select two to four one-year-old canes to be this year's fruiting canes. Cut back each of these to about 15 buds per cane. Next to each fruiting cane, leave a one- to two-bud spur cane. These "renewal spurs" will produce the fruiting canes for the following year. By this method, you can maintain fruiting close to the trunk. Remove all other canes.
To spur prune, prune main canes to leave two- to three-bud spurs, four to six inches apart. Remove all other one-year-old wood.
If your soil needs amending, now is the time to spread compost. Compost provides nutrients for plant growth, increases soil organic matter, improves soil structure and mitigates soil erosion. A compost application can affect plant growth over multiple seasons. How much to apply depends on your goals and the nutrient content of the compost.
Compost is most commonly applied in vineyards as a fertilizer. Grapevines generally require less fertilization than many other crops as growers seek to balance vegetative growth and fruit yield. Too much nitrogen can lead to excessive vegetative growth and poor fruit production.
Prior to determining an application rate, you need to know the nutritional analysis of the compost. That analysis will also determine if compost is the most appropriate fertilizer for you. If your vines need only a small amount of potassium or phosphorous, you might be better off with a commercial fertilizer containing only those nutrients. Most compost contains a wide range of macro- and micro nutrients, including nitrogen, phosphorous, potassium, calcium, magnesium, boron, iron, copper and manganese. If your vines don't need all those nutrients, a “complete” fertilizer like compost may not be the best choice.
Regardless of the time of year, you should apply fertilizer only if necessary. There is no single recipe for managing vine nutrition.Low to moderate soil fertility can improve grape quality, and multiple small applications are better than a single large one.
If you would like more information on grapevine care and some hands-on pruning instruction, register for the Napa County Master Gardeners'“Home Vineyard” workshop (information below).
Workshops: U. C. Master Gardeners of Napa County will host a workshop on “Home Vineyard: Part 1” on Saturday, February 27, from 9:30 a.m. to 2:30 p.m. at the University of California Oakville Experimental Station, 1380 Oakville Grade Road, Oakville. What to do, what to look for, and what to plan for in the vineyard between February and August. Workshop will be presented in two parts. The morning (9:30 a.m. to 11:30 a.m.) will be classroom discussion. The afternoon (12:30 p.m. to 2:30 p.m. will be a field trip to a local vineyard. On-line registration (credit card only); Mail-in/Walk-in registration (cash or check only).
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/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.