Growing Raspberries

There are 3 varieties of raspberries available for home gardener — red, purple, and black. Blackberries may be available, but differ from raspberries in that the "core" stays in the fruit when it is picked. The canes of raspberries grow upright while black raspberry and blackberry canes are long and trailing.

Most raspberries bear red fruit but a few have white or yellow berries. Most ripen in July, some in September or October, and some in either season according to when they are pruned. For varieties fruiting in summer, pruning is carried out immediately picking has finished, the old canes being cut out completely and replaced by the new canes from the perennial rootstock which will then fruit the next year. With autumn-fruiting varieties the fruited canes are cut back during the dormant season (usually in February) and the new canes which appear in spring will fruit in the autumn of the same year.

Site Selection

To get the most out of your raspberry planting, you must choose your planting site carefully. Raspberries prefer full sunlight and grow best in well-drained, sandy loam soils rich in organic matter. Clay soils are not well suited to growing raspberries. Avoid low areas that remain wet late into the spring, but select a site with access to a water supply. Irrigation is important for good plant growth during dry periods and can improve fruit size and yield.

Do not plant raspberries where tomatoes, potatoes, peppers or eggplant have been grown within the past four years, because these crops carry a root rot, called Verticillium, which can also attack raspberries. Destroy all wild raspberry and blackberry plants within a distance of 600 ft.(183 m) of the site if possible, to reduce the possibility that virus diseases might spread to your planting.

Soil Preparation

Getting the soil ready for raspberries may take up to two years, depending on its condition. Test the soil to determine it pH and fertility levels. Raspberries prefer a soil pH of 5.6 to 6.2; this may require applications of ground limestone to increase the pH of more acid soils. Soil testing information is available from your county Cooperative Extension office.

The level of organic matter in the soil can be improved and perennial weeds discouraged by sowing a cover crop, such as buckwheat, rye, millet or oats, and plowing it into the soil before it goes to seed. There should be time enough for two sowings in a single season.

Applications of barnyard manure or compost and repeated tilling for a full season can be substituted for cover cropping. However, be aware that animal manures may contain weed seeds that can become a problem in your planting later.

In the spring of the planting year, spread 25 pounds (11.3 kg) of 10-10-10 garden fertilizer per 1,000 square feet (93 square m) of the planting site. Organic fertilizer sources, such as compost, manures, sul-po-mag and rock phosphate, may be used in place of synthetic fertilizers.

Apply enough of these materials to deliver two pounds (.9 kg) each of nitrogen, phosphorus (P2O5) and potassium (K2) per 1,000 square feet (93 square m). Cultivate the soil several days before planting to incorporate the fertilizer and break up any clumps or clods.

Description of Raspberries

The crowns and roots of raspberry plants are perennial, but individual canes live two years. Each spring, the plants produce canes from buds on the crown and underground lateral stems. These canes grow vegetatively during the first season, overwinter, and produce fruit during the summer of the second year, while new canes emerge to provide a crop for the following year.

Second-year canes die shortly after fruiting. Everbearing raspberries bear a crop on the tips of first-year canes in the fall, followed by a typical summer crop on the lower portion of the canes the second year.

It's easy to tell first-year canes from second-year canes. First-year canes have green stems, while second-year canes have a thin, brown bark covering them.

Shoots may arise from 2 places — from buds at the base of the old canes and from buds on roots. Red raspberries and blackberries produce shoots or "suckers" from both places and will usually fill in a row very quickly. Purple and black raspberries do not produce suckers, so shoots occur in groups or "hills" instead of being scattered throughout the row.

Although a wide selection of raspberry varieties is available, only a few will do well under the short growing seasons and severe winters of northern climates. Select only those that are rated very hardy and early or mid-season ripening.

Use only healthy plants that are known to be virus and disease free. Propagating diseased plants will cause the disease to spread and shorten the life of the planting.

In general, red raspberries are the hardiest type, followed by purple raspberries, black raspberries and blackberries. Temperatures below 5 degrees F will injure or kill blackberry and most purple and black raspberry canes, so these should only be planted in southern parts of Maine and New Hampshire, on protected sites.

Order your plants from a reputable nursery or garden dealer. Specify disease-free, virus-indexed stock. Most raspberries are sold as dormant, one-year-old canes, but some nurseries offer plants generated by tissue culture, or micropropagation. Tissue-cultured plants may be more expensive, but they are less likely to have disease problems.

Do not store plants any longer than necessary. Store plants for short periods by placing in a plastic bag in a refrigerator or other cool place. Sprinkle dry roots with water before storing. Do not leave roots soaking in water as this kills the plant. If plants must be held for more than 1–2 weeks, they can be placed upright in a hand dug trench with the roots covered.

How to Manage

Raspberries should be planted early in the spring after the danger of severe frost is past (in late April to early May). Do not allow plant roots to dry out prior to or during planting. Plants should be set at the same depth or slightly deeper that they were in the nursery. Firm the soil around the roots and water the plants. If one-year-old canes are used, cut them back to a height of four to six inches (15 cm) about the ground.

Red raspberry plants are typically grown in a hedge row. Crowns should be planted about two feet (60 cm) apart in rows that are eight to 12 feet (3.6 m) apart. Choose the wider spacing if you'll be using large equipment, such as tractors, in the planting. The plants will soon send up suckers from the roots and crowns to form a hedge, which should be maintained at 12 to 18 inches (30 to 45 cm) wide.

Purple and black raspberries and blackberries only produce suckers from the base of the crown and will not fill out a hedgerow as red raspberries do. For this reason, they are frequently grown in the hill system to get the most production out of individual plants. For this system, plants should be set four feet apart in rows eight to 12 feet (3.6 m) apart.

Black and purple raspberries are propagated by "tip layering". Shoot tips are bent downwards and inserted about 8 cm into the soil in late summer. Roots and shoots are produced by the buried portion of the shoot. The following spring the "tip" plants can be severed from the mother plant, dug, and transplanted.

All raspberries should be grown with some sort of a trellis. This will improve fruit quality, make harvesting easier and reduce disease problems. Trellises also make pruning simpler by encouraging new cane growth to occur in the middle of the row, rather than the outside edges. For plants grown in a hedgerow, the "T" or "V" trellis systems are recommended.

For the T trellis, sturdy posts should be set in the row with 3 1/2-foot (1 m)-long cross arms affixed at a height of 3 1/2 feet (1 m). The posts should be set at least two feet (60 cm) deep in the ground and anchored at each end of the row. Secure heavy-gauge wire along the length of the row on each side of the cross arms.

For the V trellis, two posts should be set at each end of the row at about a 30 degree angle such that they are 3 1/2 feet (1 m) apart at a height of 3 1/2 feet (1 m). The wire is run from each post at 3 1/2 feet (1 m). After pruning, the fruiting canes should be tied to the wires on each side.

For black and purple raspberries and blackberries grown using the hill system, a study post should be set next to each plant (four feet (1.2 m) apart in the row). A wire can be run along all the posts in the row, about 4 1/2 feet (1.3 m) above the ground. The fruiting branches of each plant should be spread along the wire, or the canes of each plant can simply be tied to the post next to them.

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