Grapevines in Napa are still dormant and enjoying their winter nap, but this doesn’t mean home grapegrowers have nothing to do. Bud break is occurring and the annual growth cycle will commence.
If you haven’t done so already, get out your pruning shears, sharpen them and make sure they are functioning properly. Prior to bud break, vines enjoy a haircut to be at their best when bud break occurs.
When to prune can be a bit of a guessing game. Prune too early and a late frost may damage the buds. Prune too late and spring growth will start slightly later, possibly delaying veraison and, ultimately, fruit ripening.
The purpose of pruning is to:
- eliminate dead, broken or diseased wood;
- eliminate older, non-productive or marginally productive wood;
- encourage development of new wood where future crops form.
Pruning also opens the canopy to sunlight, air and spray penetration, facilitates pruning, thinning, and harvesting, and keeps vines to the desired size.
Many home grapegrowers prune their vines too lightly. You should aim to remove 90 percent of the wood produced the previous season.
There are two types of grape pruning: cane pruning and spur pruning. Prune mature plants yearly to remove all growth except 1-year-old fruiting canes and renewal spurs.
Grapes are produced from buds that will grow into shoots on 1-year old canes. The most fruitful canes are those that were exposed to light during the growing season. They are thicker than a pencil and as close to the trunk as possible (when cane pruned).
To cane prune, select two to four new fruiting canes per vine. Cut them back to leave about 15 buds per cane. For wine grapes, leave 20 to 30 buds per vine. In table grapes, leave 50 to 80 buds per vine. Leave a one-or two-bud spur cane near the fruiting cane with one or two buds each. These “renewal spurs” will produce the fruiting canes for the following year and thus maintain fruiting close to the trunk. Remove all other cane growth.
Most table grapes produce the highest yield of good-quality fruit when cane pruned.
To spur prune, prune along main canes to leave two- to three-bud spurs, each four to six inches apart. Leave no more than 20 to 80 buds per plant, depending on the type of grape. Remove all other one-year-old wood.
If you have access to a chipper-shredder, chip the pruned wood to make an excellent mulch that you can use anywhere in your vineyard or garden.
If your soil requires amending, now is the time to spread compost. Compost provides a slow release of nutrients for plant growth, increases soil organic matter, improves soil structure and mitigates erosion.
You can purchase compost from local waste-management companies. You can have a truckload delivered, or you can load up your own pickup truck or even just a few containers.
A compost application can affect plant growth over multiple seasons. How much and how often to apply it depends upon your goals as a grape grower and the nutrient composition of the compost.
Grapevines generally require less fertilizing than many other agricultural crops, as growers seek a balance between vegetative growth and fruit. Too much nitrogen can lead to excessive leafing and poor fruit production.
Before purchasing compost, ask for its nutritional analysis. This will help you determine the application rate or whether it’s even the most appropriate fertilizer for your vineyard’s needs. If you want to apply only a small amount of potassium or phosphorous, you may be better off using a commercial fertilizer containing those specific nutrients. Most compost contains a wide range of macro- and micronutrients, including nitrogen, phosphorous, potassium, calcium, magnesium, boron, iron, copper and manganese. Use it only when your soil would benefit from all these nutrients.
The key to proper fertilization is to apply fertilizer only when necessary. There is no recipe for nutrition management. Low to moderate soil fertility can improve wine quality, and multiple applications are better than a single application.
In a few months, you will move on to leaf pulling, shoot thinning, cluster thinning and berry thinning — all to aid in the health and success of your vineyard. Disease management, including the use of approved organic pesticides, should also be your focus in spring.
Workshop: U.C. Master Gardeners of Napa County will host a workshop on “Home Vineyard Part 1” on Saturday, Feb. 24, from 9:30 a.m.to 2 p.m. The Master Gardener Integrated Grape Team will explain what to do, what to look for and what to plan for in the vineyard between February and August. The morning session will be a classroom discussion of growth cycle, pruning and training and basic cultural practices for growing table or wine grapes in the home garden.
There will be an afternoon field trip to a local vineyard, weather permitting. Participants should be prepared for outdoor conditions, wear good walking shoes or boots, and bring lunch. There will be a 30-minute lunch break. Location address provided upon registration. Reserve your spot: https://ucanr.edu/survey/survey.cfm?surveynumber=21969. Mail-in/walk-in registration (cash or check only).