Climate + Site
Raspberries generally grow from zones 3 to 9, but you'll need to find a cultivar that's appropriate for your climate. In Northern areas, try extra-hardy cultivars such as Boyne, Nova, and Nordic. In the South, try heat-tolerant Dorman Red, Bababerry, and Southland.
Find a site with full sun and good air circulation. Avoid places where high winds can whip the canes around and damage the plants. The site should be at least 1,000 feet (30 m) from any wild blackberries or similar bramble berries that could share problems. Provide fertile, well-drained soil that hasn't been used to grow bramble berries, tomatoes, potatoes, peppers, eggplants, or roses, which can leave behind diseases that attack raspberries.
Buy only certified disease-free plants. You can get the bareroot, in containers, or as tissue-cultured plantlets. Your best option is probably vigorous, year-old, bareroot plants that have been propogated from virus-indexed stock.
Raspberries come in several colors. Yellow and red are the hardiest and are very sweet. Black raspberries are delicious but also the least hardy and the most susceptible to disease. Purple raspberries fall somewhere in between red and black.
Select raspberry cultivars that ripen at different times to spread out your harvest. For example, you could plant early-ripening, red summer raspberries such as Algonquin and chilliwack, then black raspberries such as Bristol, then ever-bearers such as Autumn Bliss and Heritage.
Planting + Care
Plant red and yellow raspberries 2 feet apart in a row, and they'll fill in solid in a year or two. Space black and purple raspberries 3 feet apart. Keep the row width fairly narrow—6-24 inches wide—to allow every cane to get plenty of sun and be fully productive. Mow or till along the edge of the row as needed to keep the raspberries from creeping out.
Apply compost and a little balanced organic fertilizer in late winter, if needed, for good growth. Mulch to discourage weeds and keep the soil evenly moist; water during dry spells. Propogate by division or layering, but only if you are sure your plants are healthy. In many cases, you're best off buying new, certified disease-free plants.
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Pruning and Training
Regular pruning will encourage your plants to produce high yields of top-quality berries. For a single fall crop on ever-bearers, simply cut off all the old canes at ground level when they are done fruiting.
Summer-bearing red raspberries produce fruit on 2-year-old-canes. Cut down the old, grayish brown fruit-producing canes after you harvest, but leave the new, current-season canes to produce berries next year.
In late winter, remove the smallest canes to leave three to six sturdy canes per foot of row.
Black and purple raspberries produce fruit on side branches that grow off the older canes. During summer, cut off the fruit-producing canes after your harvest, and snip off the tips of new canes when they're 3 to 4 feet tall to make them branch. During the dormant season, remove the smallest canes to leave four to six sturdy canes per foot of row. On the remaining canes, cut out any spindly side branches and trim the remaining side branches back to 8 to 10 inches long.
Harvest berries when they're sweet and ripe. Eat them promptly, dry or freeze them. Berries do not keep ripening after harvesting. For best flavor and ease of picking, wait until they are fully ripe. Some raspberries offer a slight resistance to picking even when fully ripe. Let your taste tell you when to pick. Red raspberries vary in color at maturity from light to dark red. Some purple ones change from red to purple to almost black, with sugar levels increasing as the color darkens. Raspberries slip off the stem when picked, leaving a hollow inside the fruit.
Pick your berries as early in the morning as possible, when they are cool. If the berries are wet, let them dry before picking. Handle them gently and place, don’t drop, them into a shallow container. Refrigerate immediately.
It’s easier to pick berries with both hands free. Tie two long strips of sturdy cloth like apron ties to a large tin can or small bucket. Tie your picking can around your waist, or hang it around your neck. Put your berry basket in the bottom if you like. Carry an extra basket to put overripe or moldy berries in as you pick; removing these berries will help prevent rot problems from occurring later.
Problem Prevention + Control
Several fungi diseases may attack raspberries. Powdery mildew can cause a white coating on fruit, leaves and shoots. Anthracnose produces dark blotches on canes and possibly sideshoot dieback. Cane blight causes wilted shoot tips and dark spots on the canes. Proper pruning, as previously described, should prevent many of the problems. If these diseases were a problem the previous year, spray with lime-sulfur when the buds begin to turn green. Check catalogs for resistant cultivars.
Viruses may produce stunted growth, curled, yellow-marked leaves, and/or crumbly, malformed berries. There is no cure; dig and destroy infected plants. Start a new patch in a different site with certified virus-free plants.
Crown gall can cause lumpy swellings on the roots and the base of shoots. Dig up and destroy infected plants. Replant new stock in a different site. Avoid wounding stems.
Bright orange spots on the undersides of leaves in spring indicates orange rust. This incurable disease attacks black and purple raspberries, as well as blackberries. Remove and destroy infected plants.
Gray fuzz on the fruit indicates fruit rot. Pick and destroy infected berries. Gather ripe fruit daily.
Borers are insect pests that damage canes, causing wilted shoot tips. Look for a small entry hole near the base of the wilted area. Prune off damaged tips or canes, borer and all. If the shoot tip is wilted but you don't see an entry hole and if the inside of the cane is discolored, a disease may be the culprit; cut off the cane at the base and destroy it.
This article is courtesy of Rodale's Ultimate Encyclopedia of Organic Gardening.