Organic gardeners can grow grapevines naturally, controlling grape pests and diseases without using chemical pesticides or fungicides.According to the Environmental Working Group, imported grapes are number 10 on the dirty dozen list for carrying the highest pesticide load. Organic gardeners can grow this easy crop at home and enjoy this sweet treat safely.
Choosing Grape Varieties
Gardeners should consult their local county extension agent to find out what grape diseases are prevalent in their area, and choose resistant grape varieties accordingly. ‘Rosette’ and ‘Alwood’ exhibit black rot resistance, which is the most important disease in the East. Gardeners with mildew problems can grow the resistant ‘Buffalo’ or ‘Clinton’ varieties. ‘Dutches’ is one of the few varieties resistant to anthracnose.
Planting Grapevines
Gardeners can plant grapevines in the spring or fall, when mild conditions encourage strong root development. Grapes like a slightly acidic soil pH of 6.0; gardeners with more alkaline soils can lower the acidity with the addition of organic material like compost and leaf mold. Grapes require a sturdy support and many gardeners are enchanted with the idea of grapevines laden with fruit draping over their pergola. This is fine, but gardeners must be prepared to protect the exposed fruit from hungry birds.Although gardeners commonly picture grapes as a crop grown in large fields in rural areas, grapes are surprisingly adaptable to container culture. The gardener must choose a large pot, at least 16 inches in diameter, as this will be the vine’s permanent home. Plant a small variety like ‘Delaware’ in two parts organic potting soil combined with one part compost. Container-grown grapes thrive when gardeners give them fresh soil every few years.
Organic Fertilizer for Grapevines
Grapevines are heavy feeders, and need regular fertilizer applications each spring. Potassium, or potash, is the most important nutrient required by grapevines to produce quality flowers and fruit. Organic gardeners can apply a side dressing of rock potash around the base of each vine, which supplies 10.5% potassium to plants. Rock potash isn’t soluble and will linger in the soil for the entire growing season, supplying grapevines with potassium as needed.
Organic Pest Control for Grapes
Several kinds of caterpillars feed on grapes and their foliage. Organic gardeners should encourage bat populations to control the moths that lay caterpillar eggs. The bacterial control agent Bt also controls caterpillars.Mite outbreaks can cause grapevine damage during hot, dry conditions. Gardeners should minimize dust to reduce stress to plants by applying mulch, planting cover crops, and spraying vines with water during drought conditions.
Organic Disease Control for Grapes
Fungal diseases present the greatest challenge for organic grape growers. Mildews and rots plague grape growers in all but the driest regions. Organically acceptable fungicide controls include sulfur and copper-based formulas, but these can burn grapevine foliage when temperatures rise above 85 degrees F. Horticultural oil applied to dormant grapevines is another way to control recurrent seasonal fungal diseases.A gentler disease control method gardeners with limited disease outbreaks can try is the application of compost tea to grapevine foliage. The beneficial microbes present in this nourishing formula out-compete the pathogens, leading to disease control.