How to Grow Raspberries
There has been a great upsurge of interest in raspberry growing in gardens, due in large measure to the ease with which this excellent fruit can be frozen. There are other reasons also, including the high cost of purchased raspberries, even on a pick-your-own basis, and the advent of new and heavy cropping varieties.
One considerable advantage the raspberry has over all hardy fruits except the strawberry is the ability to come into full bearing quickly, assuming the plants are well-grown. Well-grown implies good manuring, adequate water supplies, and the early removal of, necessary to allow the plants both to fruit and renew their entire aerial system each summer.
Soil and site
The wild raspberry—Rubus idaeus—grows in the British Isles, so this native is well suited to our climate, and particularly to the wetter and cooler parts of the island. The crops in Scotland are much heavier than those obtained in the drier south-east, which points clearly to the need for goodpreparations, and in particular to the desirability of ensuring a constant supply of moisture during the growing season.
It is of equal importance to avoid water-logging in the winter months because the fine fibrous roots of the raspberry are very susceptible to bad drainage, which can lead to the death of canes. The raspberry will tolerate a reasonable amount of moist shade and, other things being equal, it is better to plant in the thin shade of protective trees or shrubs than to expose the canes to the fierce blast of the unfiltered wind. The fruit is carried on side-shoots which are very readily severed from their origins by a summer’s gale, and with the shattered shoots go all hopes of a crop. So, plant in, if you can, without going to extremes. Above all else, plant the canes in a relatively weed-free part of the garden. The raspberry cannot compete successfully with strong growing weeds. Weeds will appear, of course, and should be pulled up at an early stage, or destroyed by gentle, shallow hoeing, taking care not to cultivate deeply at any time after planting.
Propagation is relatively easy, because all that is necessary is to dig up suckers, or spawn, in the autumn and plant these rooted canes. There are one or two problems. The raspberry sometimes suffers from virus diseases, and once these are in the plant a cure is beyond all but the lavishly equipped laboratory. Secondly, and of lesser importance, new raspberryoften appear at the base of the fruiting canes. It is therefore best only to propagate your own raspberries if the plantation from which you obtain the suckers is of riotous, fecund and uniform vigour. There is an excellent certification scheme used by nurserymen, and this is much the safest bet for the beginner. It is so important to make a good start that the point is worth repeating even in the form of negatives. Never use suckers from weakly growing plantations with sparse new canes carrying light-coloured foliage. Even if free, they are much too expensive.
Varieties are numerous and mostly new. Whereas the Cox’s Orange Pippin dates from 1825, and other popular apples are even older, there are few raspberry varieties available today which were extant even thirty years ago. The change is partly due to the depredations of virus diseases, but even more to the splendid work of Research Stations who saw the need for new varieties, and who with great patience and skill bred the new and greatly improved kinds that we now have. Gardeners are incredibly fortunate in the spin-off they enjoy from research which is carried out essentially on behalf of the commercial grower.
The selection of varieties is not easy, but any modern nurseryman’s list is likely to include the following. Those marked * are best for freezing.
Mailing Orion Glen Clova*
The latest report from one research station shows that over seven thousand new seedlings were grown-on in 1975. If only one of these is an improvement on what we already have then we will have benefited. An example of the possibilities in scientific breeding lies in a brief reference in the report to one of the new late ripening varieties, named Mailing Leo, which outcropped the excellent established variety Norfolk Giant by a magnificent 60 per cent in the preliminary trials. My choice of three to cover the season would be:
Mailing Promise is a well-tried, heavy-cropping early variety.
Mailing Jewel, one from the same stable but rather later and of good freezing quality. If I had room for one variety only this would be my choice.
Norfolk Giant, a late variety which always crops well. If Mailing Leo lives up to its early promise then it will be the natural successor to Norfolk Giant, but we won’t know its real value for some years.
So far we have been considering the main summer fruiting varieties, those which produce their fruits on last year’s canes. It is surprising that the autumn fruiting varieties are not grown more widely. These fruit on the current year’s canes and prolong the season, although the crop is not as heavy as that produced by the summer fruiting kinds. Of the two varieties listed, Zeva and September, the latter is to be preferred. If you like to be different there are also yellow, summer fruiting, raspberries of which the one most frequently encountered is Yellow Antwerp.
The planting of both summer and autumn fruiting varieties is best done during the late autumn, in early November for preference. The soil at that time is still warm enough for re-rooting to take place, and plants to become established before the strain of the following growing season commences.
If late autumn planting is not feasible then any time up to the middle of March is still possible, but the earlier the better. Cover the roots with the most friable of the soil which was dug from the planting hole or, even better, with used potting soil. Spread the roots out, plant shallowly when the soil is reasonably dry, make the ground firm, and all will be well.
Space the plants 60cm (2ft) apart and, if you can manage more than one row, allow some 2m (6ft 6in) between the rows. Finish with a good mulching of the surface, although this can be deferred until growth begins, if more convenient.
Pruning begins on planting, and follows the same principle applied to newly planted black currant bushes, in that the aim is to prevent the formation of fruit (on summer fruiting varieties) in the first year. Instead all the energy of the new plant, which after all has only a limited root system, is directed to the production of new roots and new canes. Accordingly, cut each newly planted cane back to about 25cm (10in) above ground level. Unlike black currant prunings the cut shoots cannot be used asfrom which to produce new plants, because the raspberry, like so many members of the genus Rubus, has a perennial rootstock which produces only biennial stems. In other words the stems die after fruiting, to be replaced by new stems growing directly from the roots.
Pruning is therefore simple, because in a way the plants are naturally self pruning. To improve on nature, not only cut out completely the fruited canes but also reduce their numbers during the growing season. This is done by pulling out the weak surplus suckers, wearing a protective glove. The idea is to leave behind strong young canes at about 10cm (4in) apart. At the end of the season, prune out the decrepit old and tie in the triumphant young. In fact pruning can be done at any time once fruiting is over, and in some years the young cane appears to be all the better for the early removal of the previous generation.
One further act of pruning remains. In early March the tip of each cane is trimmed back to a uniform height. The purpose is to encourage the fruiting laterals to break and at the same time to remove a source of rather weak laterals at the end of the shoots. It is wise to prune the tips in spring rather than winter so allowance can be made thereby for dying-back following a hard winter. There is room for experiment here, in that the tradition with the older varieties is to cut back to about 1.75m (6ft) but the new, more vigorous ones need not be trimmed so severely, indeed it is wasteful to do so. If the canes are really vigorous then the lightly pruned tips can be bent over and secured to the top wire in a series of loops. Naturally, varieties that fruit in autumn (September) are cut down to ground level each winter, so that a new crop of canes is produced and fruit carried in the same season.
In many gardens the canes are left to support each other as best they can, with moderate results. There is no doubt that if you are looking for heavy and regular cropping combined with neatness and long life, the raspberries should be grown against posts and wire. Use stout posts, with end struts. Space each post about 3m (10ft) apart, and standing 2m (6ft 6in) out of the ground. Three wires are stapled to the posts, one at the top, the bottom one 60cm (2ft) from the ground and the other mid-way between the two. It is possible to contrive simpler and less expensive supports, but none so satisfying. There is no reason, however, why raspberries should not be grown in clumps rather than rows, each clump being supported by a single post. Whichever system is used take care to prevent the suckers straying away from the parent plant.
It is tiresome but necessary to repeat that the best results follow on the incorporation of large quantities of farmyard manure or composted vegetation or other moisture-retaining bulkybefore planting. This foundation should be supplemented by an application of sulphate of potash to the soil at 33g per m2 (1oz per sq yd), and the whole status maintained subsequently by an annual mulching of whatever is available, including lawn clippings. Thereafter be guided by the performance of the plants. Raspberries respond to supplies of potassium and on soils which tend to be low in potash the dressing mentioned above may be necessary as an annual rite of spring. If growth generally is unsatisfactory, despite the liberal use of bulky organic materials, then apply a general compound fertilizer in the spring. Growmore at 100g per m2 (3oz per sq yd) is about right. More concentrated compounds should be used at lesser rates according to analysis.
Pests and problems
On really heavy clay soils that tend to lie wet it is possible to overdo the mulch to the extent of excluding air from the soil and bringing about soil stagnation and the death of canes. But such soils will not need mulching in any case, save in drought years. Another risk, worth taking, is that mulching sometimes encourages a tiny pest called cane midge, which feeds just below the rind of the cane and allows disease to enter. Carry on mulching, if you can, and deal with midge if it occurs.
Much more troublesome than cane-midge is the loathsome raspberry beetle, which gives rise to maggoty fruits. Dust the fruitlets with derris or spray with malathion as soon as the first pink fruits are seen. Aphids also can be a nuisance, but are easily-dealt with by spraying with malathion or other suitable aphicide as soon as the colonies appear. The most difficult of the fungus diseases is called cane-spot, but this is at its worst on loganberries.