Scientific NameVitis vinifera (wine grapes) Vitis labrusca) (table grapes)
General InformationPhoto: Luca, Unsplash
When to Plant
Plant dormant or green growing vines in the early spring.
Grapevines prefer full sun, ideally seven to eight hours per day.
Although grapes thrive in a wide range of soils, their roots do not like sitting in wet or damp soil. Plant them in an area with good drainage. In poor (or clay) soil, add a large quantity of compost into soil before planting.
Grapes need lots of space for good air circulation. Allow about eight feet between each vine where soil is marginal, and up to 12 feet with deep, rich soil (if the soil is richer, the vine’s roots will spread farther, therefore they need more room). Vine spacing within the row can be six to nine feet apart.
Grapevines require strong structures for support, such as a trellis, arbor, or fence. If you have the space, an arbor may be ideal. It also doubles as an eye-catching focal point in a garden.
Home gardeners can grow grapes on arbors. Use one vine per 50 to 100 square feet of arbor space, or more if vigorous varieties are used. A healthy vine will take up a minimum of about 50 square feet of arbor space, and vigorous varieties or vines grown in deep, rich soil should be given 75 to 100 square feet or more.
Grapevines will grow and produce well in a wide range of soil types, but good drainage is very important. Roots tend to grow deep – up to 15 feet deep -- although most of the roots grow in the top three feet of soil. Therefore, soils should be at least three or four feet deep above hardpan, stratified layer, or rock. With careful management, two feet of soil can be adequate.
The best wine quality often comes from vines that are grown on less fertile and rocky soils. Less fertile soils often produce smaller berries, which is preferable for wine making because it gives a greater skin to juice ratio.
Irrigation is essential for good vine growth and production. Grapes will adapt to low water conditions, but fruit production will be reduced. Apply water deeply, thoroughly filling the root zone with water. Irrigation frequency will depend on the soil type and depth, the rooting depth of the vines, and the weather. Drip irrigation is an excellent method; the frequency of irrigation should be once a week or more often.
Timing of irrigation is a critical factor for producing the best quality grapes. Avoid water stress from the bloom period to fruit softening, which occurs when fruits give in to finger pressure. Usually, color begins to appear on colored varieties at the same time. Grapes on the vines may succumb to cracking if the vines are allowed to dry between waterings. Maintain an even level of soil moisture to avoid cracking. Also avoid excessive irrigation to prevent having more vine than fruit.
Given good drainage, grapes are well adapted to a wide range of soils and generally have few nutritional needs. However, in some areas nitrogen, zinc, and potassium may become deficient. If deficiencies do appear, applying these nutrients at the right time and in the proper amounts contributes significantly to a successful crop. Refer to this guide to fertilizer management for grapes.
Over-fertilizing with nitrogen can be a problem, whether the nitrogen source is a fertilizer or a leguminous cover crop that fixes nitrogen. Nitrogen fertilizer should be used sparingly on grapes unless a specific deficiency has been diagnosed. Fertilizing with high levels of nitrogen can contribute to excess vegetative vigor in the vines and may reduce fruit set, fruit quality, or both.
The development of flower clusters on the emerging shoots usually starts in mid-March, and the flowers typically begin to bloom in May.
Most grapes are self-fruitful, so cross pollination is seldom necessary.
Most cultivated grapes have “perfect flowers,” with a normal ovary and pistil and fully developed, upright anthers. (In other words, they are both male and female.) This means that cultivated grapes are mostly able to set fruit by self-fertilization, with a few exceptions.
Grape flowers have a protective cap, known as a calyptra, which covers the male and female sex organs until bloom. The calyptra cracks open from the bottom and exposes the flower parts to pollination, which must occur before berries can develop.
Grapes will not continue ripening once picked from the vine. Test a few to see if they are to your liking before harvesting, usually in late summer or early fall. Grapes are ripe and ready to harvest when they are rich in color, juicy, full-flavored, easily crushed, but not shriveled, and plump.
StorageN / A
Good Varieties for Marin
For good table grapes, consider: 'Thompson seedless' (white), 'Autumn Royal' (purple-black, seedless), 'Catawba' (red, aromatic), 'Niabell' (blue-black, excellent on arbors), 'Niagara' (light green, good on arbors), and 'Red Globe' (pink-red).
If you are tempted to try wine grapes, Marin’s warmer, northern interior portions are best. In milder, more coastal areas of Marin, fruit production will suffer from chronic pressure from powdery mildew and other diseases.
Three types or species of grapes are available:
American varieties (Vitis labrusca) such as 'Concord' and 'Niagara'
European varieties (Vitis vinifera) - the predominant wine, table, and raisin cultivars grown in California
American hybrids, which are crosses of European and American species. Generally, American types are more cold hardy than European types. The two types also differ in their fruit characteristics and growth habits. European varieties generally require a longer growing season to mature their fruit, although most grape varieties need some summer heat to produce good-quality fruit.
Winter dormant season:
Prune to remove 75% to 90% of last year's growth and to maintain the form of the vine in the location desired. Almost all varieties can be cut to reduce canes to short spurs. Leave three buds on each spur if the canes are fat (diameter of thumb) two buds on medium canes (index finger size), and one bud for pencil diameter canes. Cane pruning is required for 'Thompson Seedless', but will work for any variety. Leave three to six canes containing 10 to 15 buds, depending on the vigor of the vine. Vines with numerous fat long canes can support many long fruiting canes. However, those with short skinny growth should be pruned back heavily, leaving fewer canes and buds per cane. Generally, 30 to 50 buds are left per mature vine regardless of the pruning system. Daub pruning wounds with benomyl immediately after pruning to control Eutypa (a fungal disease) dieback.
Spring bloom season:
Provide frost protection in cold areas by covering tender shoots with cloth or paper to reduce heat loss to the atmosphere. Dust or spray at two week intervals to prevent powdery mildew. Use dusting sulfur, wettable sulfur, or a one percent solution of soapy water. American varieties and hybrids are resistant to powdery mildew and need not be treated. Fertilize mature vines with one pound of urea or 20 pounds of manure at bloom time. Water fertilizer in.
Summer growing season:
Provide frost protection in cold areas by covering above tender shoots with cloth or paper to reduce heat loss to the atmosphere. Dust or spray at two week intervals to prevent powdery mildew. Use dusting sulfur, wettable sulfur, or a one percent solution of soapy water. American varieties and hybrids are resistant to powdery mildew and need not be treated. Fertilize mature vines with 1 pound of urea or 20 lbs. of manure at bloom time. Water fertilizer in.
Fall harvest Season
Remove all clusters of grapes and enjoy the fruit. Do not leave mummies of old fruit hanging on the vine. For the next season, control weeds around the base of the vine with up to three inches of organic mulch.
In Marin, a common disease in grapevines is powdery mildew, which covers the woody stems and fruit with a powdery white fungus. Dusting your plant with sulfur can help. (Or try to buy varieties that are resistant to powdery mildew, such as 'Niabell' or 'Niagara'). Another problem is bunch rot, which causes grapes to shrivel in late summer. This can be reduced by thinning berry clusters early and removing leaves around clusters to improve air circulation.