Here at Gardening Know How we get lots of questions, and our goal is to provide answers to those inquiries to the best of our knowledge. Growing grapes in the landscape is a popular endeavor for many gardeners, and one that includes many issues. As a result, we receive a number of questions about grapevines in the garden. Here are the top ten.
Growing grapevines prefer a well-draining sandy loam with a pH of 5.5-6.5. That said, grapes are fairly tolerant of their soil conditions provided they are neither too alkaline or too acidic, have sufficient organic content and are well-draining.
Almost all commercially produced and grown grapes are self-pollinating. This means that they do not require another grape to set fruit. Wild grapes, on the other hand, usually require a male and a female plant to produce grapes. If you have the space though, plant two just for variety.
Grapes should always be pruned during their dormant period in the winter. In order to promote fruiting, be brave and prune hard. Be sure to cut off as much of the old wood as possible, which will, in turn, encourage production of new shoots and vines upon which the fruit is produced. When pruning grapes that require winter protection, the goal is to prune into one horizontal trunk that can easily be removed from the support structure. Otherwise, remove all growth except new fruiting canes and renewal spurs. Select a branch and cut it back 3-4 feet (around a meter), leaving at least a two-bud renewal spur. Tie this cane to the support and remove all other canes. At the end of the growing season, cut off the old trunk just below the renewal cane.
Grapes have a deeply growing root system and, as a result, unless your soil is very poor, usually require very little additional fertilizer. The only way to really be sure is to do a soil test; grapes like a pH of 5.5-7.0, so amend accordingly. Thereafter, give the vine a light fertilization with an all-purpose 10-10-10 food at the rate of no more than ¼ pound (113 g.) applied in a circle 4 feet away from each vine. If you would rather use manure, apply 5-10 pounds (2-4.5 kg.) of poultry or rabbit or 5-20 pounds (2-9kg.) of steer or cow manure per vine. Urea, ammonium nitrate and ammonium sulfate can also be used to fertilize the grape after the vine has bloomed. Fertilize grapes just when buds emerge in the spring.
Grapevines do not usually produce their first year, although it depends on how old the vine was when purchased. Generally, grapes begin producing in their second year but these should be snipped off to allow the vine to focus on strengthening its root system. By the third year, a healthy vine should be producing grapes for harvesting.
A grapevine that is not producing could be the result of several of factors. It could be that the soil pH doesn’t suit the vine; grapes like a pH of 5.5-7.0. They also do not like soil that doesn’t drain well or has a surfeit of nitrogen. Do a soil test and then amend the soil if necessary. It may be that the vine does not get sufficient light. Pruning hard will go a long way to giving the vine access to more light and a hard prune actually encourages growth. Most hard pruning should be done every winter when the plant is dormant, but some cultivars such as Concord, Crimson Seedless, and Thompson seedless are cane pruned in the spring and early summer. Most grapes are self-pollinated, but there are a few that require a partner or they will not produce. If your grape is a Riverbank grape or Muscadine, it needs partner in order to produce grapes.
Grapevines have deep tenacious roots, so if you need to move the vine, you will either need a backhoe or a strong back and a willingness to sweat. If you are up for it, the best time to transplant a grapevine is in the fall or early spring. Cut the vine back to 8 inches (20 cm.) from the ground. Dig around the trunk to locate the peripheral roots and then start digging them free from the soil. Once these outer roots have been freed, dig a deep vertical trench around the vine and lever it from the earth. Move the vine to a hole that is twice as wide as the root system. Loosen the soil at the bottom of the hole to accommodate the roots and then fill in. Water the vine frequently as it establishes.
Black rot of grapes should be treated between bud break until around four weeks after bloom. Use Captan or Myclobutanil fungicides. Otherwise, prevention is the best management option. Remove any mummy grapes and all grape detritus from the ground in the fall. Prune out any afflicted vines and don’t be afraid to prune heavily. In the spring, if any lesions pop up, remove them ASAP and begin fungicide applications.
Grapes grow quite well in containers if you follow a few guidelines. First of all, you need a container that is at least 15 gallons with drainage holes. The container can be made of almost anything but keep in mind that some materials absorb heat and might make the roots of the plant too hot. Next, you need a sturdy trellis or other support. Now you just need to plant your grape. Grapes are tolerant of most soil types but prefer a well-draining, sandy loam with a pH of 5.5-6.5. Grapes do not need additional fertilizer, but if you do decide to feed the vine, do so with a low nitrogen food. Keep the container consistently moist.
Grape winter protection depends on your USDA zone. Some areas can get away with mounding 8 inches (20 cm.) of snow over the vines, while colder regions need to add insulating mulch like straw or shredded cornstalks to protect the vines. If your area gets cold but doesn’t snow, the vines should be covered more deeply, say with a foot or two of soil. Some gardeners go to extremes and actually plant the vine in a deep trench. As the plant grows, more soil is added. Others use a shallow trench and the dormant vines are removed from their supports, wrapped in old blankets or burlap and then placed into a slightly sloped trench lined with sand. A second layer of protective covering place atop the vines along with black plastic or insulating fabric and is then secured with soil or rocks.
We all have questions now and then, whether long-time gardeners or those just starting out. So if you have a gardening question, get a gardening answer. We’re always here to help.