Growing Blackberries Organically

Blackberries are vigorous, long-lived, and easy to grow organically in much of the US, as long as you start with clean plants, choose a cultivar suited to your winters, and keep wild blackberries away from your planting. Wild blackberries matter because they are a reservoir for the three problems organic growers can't spray their way out of: viruses, orange rust, and (in the Southeast) rosette. The rest is annual pruning and a sturdy trellis.

Growth types: erect, semi-erect, and trailing

Blackberry cultivars are grouped by how their canes grow. The type determines spacing, the trellis you need, and where the plant will survive the winter.

This breakdown follows Oregon State University Extension's home blackberry guide, which calls erect types the most winter-hardy and trailing types the least cold- and heat-tolerant. It also notes that most modern cultivars are thornless.

Blackberries also differ in which canes fruit. Floricane-fruiting types bear on second-year canes. Primocane-fruiting types, sold as "everbearing," can fruit on first-year canes as well. University of Arkansas guidance notes that primocane yields vary greatly by location.

Match the cultivar to your winter

Chilling needs vary a lot between cultivars. The same Arkansas publication lists 'Kiowa' at roughly 200 to 300 chill hours and 'Apache' and 'Navaho' at roughly 800 to 900. For choosing by region, see blackberry chill hours.

Site, soil, and spacing

Full sun and well-drained soil are the baseline. Recommended pH differs slightly by source: NC State Extension and Arkansas give 5.5 to 6.5, Oregon State gives 5.6 to 6.5, and Clemson's Home & Garden Information Center gives 6.0 to 6.5. A pH of 6.0 to 6.5 falls within all three ranges. Oregon State notes that blackberries tolerate wet soils and don't need raised beds. Arkansas still recommends beds 6 to 10 inches high where drainage is poor.

• Erect types: 2.5 to 3 feet apart in a hedgerow (Oregon State). NC State gives 3 to 4 feet.
• Semi-erect: About 5 feet apart (Oregon State).
• Trailing: 3 to 5 feet apart (Oregon State). NC State gives 6 to 8 feet.

The sources don't explain the differences. Follow your own state's guidance where it exists. Test your soil first. See soil test results explained.

Tipping and pruning

Blackberry pruning follows the cane cycle. Floricanes fruit and then die, so remove them after harvest. Primocanes are next year's crop, so manage them for branching.

1. Summer tipping. Cut the tips off new erect canes to force side branches. Clemson says to do this at 30 to 36 inches. Arkansas says 36 to 48 inches. Oregon State suggests about 3 feet for erect types and 4.5 feet for semi-erect.
2. After harvest. Cut spent floricanes to the ground.
3. Winter. Shorten side branches. NC State says 12 to 16 inches for erect types and to keep four to eight canes per square yard. Clemson says 12 to 14 inches.

For primocane-fruiting erect types grown for a single fall crop, Oregon State says to cut all canes to just above ground in late winter. Trailing types are handled differently: Oregon State describes training new canes in bundles beneath the fruiting canes on the trellis.

Start with clean plants

Oregon State recommends buying certified, disease-free plants from a reputable nursery instead of digging suckers from a neighbor's patch. It also points out that many cultivars are patented, which is another reason not to propagate your own. The virus risk for blackberries is serious. In the Southern US, blackberry yellow vein disease is caused by a complex of viruses rather than a single virus, spread by pollen, nematodes, whiteflies, thrips, mites, and other insects. According to the director of the Arkansas Clean Plant Center, healthy blackberries can produce for 20 years or more, but infected plants can become unproductive in as few as five. For more on how certification works, see why berry plants should come from certified clean stock.

Rosette and orange rust

Rosette (double blossom)

Rosette is a fungal disease caused by Cercosporella rubi. A USDA Agricultural Research Service fact sheet calls it a severe disease of blackberries in the southeastern United States. Infected buds produce several to many shoots from one node, giving a bunchy look, with bronze-tinged leaves. The flowers are pinkish, distorted, and set little or no fruit. Infection happens one year and symptoms show the next.

The fungicides the fact sheet rates most effective are conventional products, not organic ones. The organic toolkit is:

• Resistant cultivars. ARS says most thornless cultivars from the Arkansas breeding program are tolerant or resistant, and 'Navaho' and 'Arapaho' develop little or no rosette at most locations.
• Pruning. Remove any stems with rosettes in early spring, before infected buds open. ARS notes the fungus is localized, not systemic, which is why pruning helps.
• Cutting back. Cut heavily infected plants back to about a foot above ground immediately after harvest.
• Wild host removal. Clear wild blackberries from the immediate area.

Orange rust

Orange rust is the opposite case. UC IPM explains that fall infections can become a permanent, systemic infection of the crown, roots, and shoots. Infected plants send up spindly, pale shoots, and the undersides of the leaves develop waxy orange pustules. Blackberries, dewberries, and black and purple raspberries can be infected. Red raspberries are not. Pruning doesn't cure it. UC IPM says to promptly remove infected plants, roots included, and to remove nearby wild blackberries.

Spotted wing drosophila

Blackberries ripen in mid- to late summer, often when spotted wing drosophila numbers are highest. Clemson recommends picking fruit as it ripens and not leaving overripe berries on the plant. The full non-spray plan is in spotted wing drosophila in home berry plantings.

Blackberries share their virus and wild-host issues with raspberries. For the full picture on site selection and clean stock, go back to growing berries organically.