Growing Raspberries Organically

Raspberries grow well organically if you get two things right at planting: drainage and clean plants. Root rot and viruses are the most common reasons home raspberry patches decline, and neither can be fixed with a spray once it's established. After that, most of the work is pruning, and how you prune depends on whether your variety fruits on first-year or second-year canes.

Summer-bearing vs. fall-bearing

Raspberry roots and crowns are perennial, but each cane lives only two seasons. In its first year a cane is called a primocane, and in its second a floricane. The type you plant decides which canes carry fruit.

The pruning steps above follow University of Minnesota Extension's home raspberry guide. For summer-bearing reds, UMN suggests thinning new canes to 4 to 5 sturdy canes per foot of row. For black and purple raspberries, it says to cut side branches back to 12 to 18 inches.

Fall-bearing types grown for a fall crop only are the simplest to manage, since every cane comes down each spring. The drawback is timing. A fall crop ripens during peak spotted wing drosophila season (more on that below).

Drainage matters more than anything else

Oregon State University Extension calls raspberries sensitive to wet or heavy soils and susceptible to root rot, and says poor drainage dramatically raises the risk of infection. Phytophthora root rot has no organic cure, and its main prevention is site choice.

• On heavy soils, Oregon State recommends mounded beds at least 1 to 1.5 feet high, or built raised beds 2 to 3 feet deep.
• UMN recommends well-drained soil and raised rows on heavy ground.
• Ohio State adds a caution: mulching can increase or aggravate Phytophthora root rot. That's a conflict with the general advice to mulch berries. Illinois Extension, for example, suggests 4 to 6 inches of well-rotted sawdust or clean straw on new plantings. If your soil drains poorly, go light on mulch or skip it near the crowns.

Site and soil

• pH: 5.6 to 6.5, per Oregon State, which suggests adjusting with lime or sulfur one to two years before planting. See soil test results explained.
• Sun and air: Full sun and good air movement. UMN ties both to less gray mold and cane blight.
• Crop history: Oregon State says to avoid ground where verticillium-susceptible crops grew in the past five years. Ohio State names tomatoes, potatoes, and eggplant grown in the previous year.
• Soil prep: UMN suggests tilling 8 to 12 inches deep and working in about 3.5 cubic feet of compost per 100 square feet. For more on compost rates, see too much compost.

Keeping viruses out

Raspberry viruses are the quiet problem. The plants don't die. They slowly get shorter and produce crumbly fruit. UC IPM says infected caneberries typically become unproductive in 2 to 3 years and that there is no cure. The viruses spread through aphids, thrips, nematodes, pollen, and infected plant material.

A few specifics are worth knowing:

• Raspberry bushy dwarf virus spreads through pollen. Oregon State notes that once a plant is infected, it stays infected, and recommends starting new plantings in a different location with certified plants.
• Tomato ringspot virus is spread by dagger nematodes in the soil. UMN warns that the nematodes stay in the soil, so you shouldn't replant red raspberries in a spot where it occurred. UMN notes that black raspberries are resistant and can go there instead.
• Mosaic is a virus complex that hits black raspberries hard. Cornell's berry diagnostic tool notes that red raspberries can carry these infections without symptoms. Ohio State advises against planting black or purple raspberries near reds, even healthy-looking ones, and says that if you must grow both, keep them as far apart as possible, with blacks upwind.

Ohio State also recommends not planting within 300 feet of wild blackberries or raspberries. Other extension services just say to remove or control wild brambles nearby. Illinois Extension recommends always buying certified nursery stock and checking plantings twice a year for stunted, unproductive plants to remove. For more, see why berry plants should come from certified clean stock.

Spacing and trellising

UMN recommends planting red and yellow raspberries every 2 to 3 feet and black and purple types 4 feet apart. Keep the row narrow. Oregon State suggests 6 to 12 inches wide for summer-bearers and 12 to 18 inches for everbearers. UMN recommends narrow rows, weeding, and thinning to improve air movement and reduce gray mold.

A simple trellis keeps canes and fruit off the ground. UMN describes wires at about 2, 3, and 4 feet high. It's worth building before the canes need it.

Spotted wing drosophila

Raspberries are a favorite host of spotted wing drosophila, and fall-bearing crops ripen right when populations peak. Pick every few days, refrigerate fruit promptly, and consider fine netting for fall crops. The full approach, including the salt test for larvae, is in spotted wing drosophila in home berry plantings.

How long a planting lasts

Oregon State puts raspberry productivity at five to 15 years, depending on type, soil, and pest pressure. Where the patch ends up in that range depends mostly on drainage and virus pressure.

Raspberries share their virus and site issues with blackberries. For the bigger picture, go back to growing berries organically.