The cultivated raspberries are derived from three species, the European Red Raspberry of North America, R. Idaeus variety strigosus, and the Blackcap Raspberry, R. Occidentalis. Hybrids between Blackcap and Red Raspberries are known as Purple Raspberries and are grown extensively commercially in New York, and in other states, as well as Canada. Several species of Oriental Raspberries are now being crossed with American varieties to produce varieties suitable for cultivation south of the latitude of Washington D.C. Where the American varieties do not thrive.
Requirements for Growing Raspberries
Raspberries require a cool, moist climate, such as is found the upper Ohio Valley. The soil may range from a deep sandy loam to a clay loam, the former being preferable. Good drainage is important, as Raspberries die out readily where the water table is near the surface for more than a few hours after a heavy rain during the growing season. The water table should be down at depth of about 3ft. The soil should be well-supplied with organic matter.
Good air drainage is desirable because minimum winter temperatures are lower in frost pockets from which cold air cannot easily drain, and fungus diseases, especially anthracnose, and spur blight are more serious where air circulation is poor.
Wild Red Raspberries and run-out cultivated Raspberries should be eliminated before starting a new planting because these may harbor virus diseases and insect pests. Land that has grown tomatoes, potatoes, peppers or eggplants should be avoided as a site for a raspberry planting for at least three years because these crops may infect the soil with verticillium wilt, a troublesome soil-borne disease of black and purple raspberries.
Soil preparation should be as thorough as for vegetables. Organic matter may be supplied by the addition of stable manure or by plowing under green manure crops. Perennial weeds should be eliminated before the Raspberries are set.
Propagation of Raspberries
Raspberries, such as the red raspberry, increases by producing many sucker plants from the roots. When increase is desired, these are dug when dormant and are used for planting. Nurseries often grow them in nursery rows for a year and sell them as transplants or two year plants. The new shoots which come up in the spring are sometimes used as planting stock and, if transplanted carefully during cool cloudy weather, are entirely satisfactory. They should be dug before they are over 6 inches high.
Black and purple varieties are propagated by tip layering. This is done by inserting the tip of the new cane vertically in the soil to a depth of about 4 inches in late August or early September, before autumn winds have injured them. Roots develop rapidly on the tips, and the “tip plants,” as they are called, are dug in the spring and used as planting stock, or grown for a year in the nursery to become transplants, or two-year plants.
Red raspberries may be planted in the fall or early spring. They are usually grown in hedge rows, the plants being set 2’ apart in the row and the suckers filling in a solid row which should be restricted to a foot in width. Rows in the garden should be 6-7Ft. Apart, or, in commercial plantings, 9-10 ft. apart, according to tillage machinery that is to be used. They are also grown in hills 5-6 ft. Apart and tied to stakes.
Trellises are often used to support the fruiting canes of Red Raspberries, especially in the West, where they grow very tall. Trellises are of doubtful value in the East, although hone gardeners often use them. A simple trellis consists of two wires about 5 ft. High and about a foot apart. The fruiting canes are tied to these wires in the spring before growth starts. Often a single wire is used rather than a pair of wires.
When the red varieties are grown in hills, a stake extending 6 ‘ above the ground is used. Seven or 8 canes may be left in each hill and tied to the stakes.
The Black and Purple varieties are set 3’ apart in the row and, as they do not produce suckers, the plants remain in hills. The tip plants by which they are propagated are best set out in the spring, but the two-year plants may be planted out in the fall.
Care of Raspberries after Planting
The main task after planting consists mostly of weed control. Cultivation should be shallow and frequent enough to keep down the weeds. After the first year the suckers of the Red varieties will spread out into the row. These must be removed periodically to prevent the hedge rows from becoming over a foot in width. After the planting is in full bearing, which will be the third year, cultivation should be stopped soon after the harvest and a cover crop sown between the rows to check late fall growth of the canes, which may predispose them to winter injury.
Mulching with straw, hay, or a similar material is a very effective method of managing the soil, especially for light soils, or where the summers are hot and dry. The mulch may be put on in early summer and allowed to remain until it decays.
Nitrogen is the material most likely to be profitable for fertilizing Raspberries. It may be used at the rate of 60 pounds to be acre, and amount that may be supplied by 200 pounds of ammonium nitrate, 400 pounds of nitrate of soda or appropriate amounts of other nitrogenous fertilizers. The fertilizer should be applied in early spring before growth starts. Stable and poultry manures are excellent for Raspberries, but they should be used with caution as they may cause too vigorous growth, which is susceptible to winter injury.