Everything You Need to Know About Growing Raspberries
Raspberries have so much going for them: because of their upright habit, they produce a relatively large crop from a very small area of ground; they are simplicity itself to prune; and by choosing your varieties carefully, it’s possible to have fresh fruit for a period of at least 4 months. Most varieties freeze well without disintegrating and so, of all soft fruit, the raspberry probably comes closest to being available in more or less the same, recognizable form all year round. Apart from having rather stiff instead of flexible canes, they differ principally (and most usefully) from related species of Rubus, such as the blackberry, in that the ripe fruit separates easily from the plug or receptacle when they are picked.
HISTORY AND TYPES OF RASPBERRY
The value of the raspberry has been appreciated since ancient times although for many centuries it was the fruit of the wild Rubus idaeus that was collected. But at first it seems they were gathered more for medicinal than food use. Rubus idaeus grows in many parts of the world, usually in woodland habitats but by the sixteenth century, in England at least, it was being planted in gardens. Although its fruits can be sweet and delicious, they are small compared with those of the cultivated raspberries that we know today. 1t’s a very variable species, however, and gradually larger-fruited forms were selected for garden cultivation and gradually, too, both red- and yellow-coloured types became available to European gardeners. The so-called yellows range, in practice, from a rich gold to an extremely pale yellow-fruited variant that was known historically as the white raspberry. There are also black-fruited species and varieties and even purples too, produced by crossing the red with the black. Black raspberries are less hardy than red, however, and have never been as popular in Europe as in North America where they originated. In the present century, a good deal of research has been devoted to producing new and better raspberry varieties, especially those with disease resistance. The North American raspberry species Rubus strigosus and several others too have been used in making the crosses.
Apart from fruit colour, modern garden raspberries are divided into two main groups depending on the way that the fruit are borne. Most raspberries fruit on the canes produced in the previous season but there is a small group of varieties, called primocane raspberries, that fruit on the tips of the current season’s canes. They bear a smaller crop but help in extending the cropping period well into the autumn. The cultivation of the two groups is similar in all respects except for.
The classic, fairly deep medium loam with a pH around 6.5 is the ideal raspberry. On wet, cold, heavy soils they will grow very inadequately while on very light, free-draining sites they will produce small, dry and tasteless fruits although this is less of a problem in areas with a high rainfall. Both heavy and light soils should, therefore, be improved with organic matter before planting but if the soil is very heavy, and very large quantities of organic matter would be required, it is generally still possible to produce a reasonable crop if this improvement is confined to the area of the trenches in which raspberries are planted, rather than over the whole plot. On even slightly alkaline soils, raspberries will display symptoms of iron deficiency which should be corrected.
As they are naturally plants of lightly shaded woodland, raspberries are tolerant of light shade in gardens, and if the soft fruit garden has a slightly shaded area, they will generally grow better there than other types of soft fruit. Nonetheless, the very best crops will always be obtained in full sun and the rows should, if possible, be orientated north-south to make optimum use of this. Shelter from strong winds is important and in very windy spots, it’s sensible to choose shorter, stiffer-caned varieties. Raspberries make a good choice in areas prone to spring frosts, however, for they flower late and usually escape frost damage.
Raspberries are best planted in the winter; early winter is ideal but any time when the soil isn’t frozen is suitable. They are, in any event, generally sold bare-rooted during the dormant season and do not establish as satisfactorily (even when obtainable) from container-grown stock planted at other times of the year. Usually, raspberries are grown in rows and I find they are most easily planted in a trench rather than in individual planting holes. Although they produce a mass of fibrous roots close to the surface, they do produce deep roots too and so the trench should be at least 45cm (18in) deep and of similar width with plenty of well rotted manure or compost dug in, and a handful of bone meal added per running metre (yard) of row.
The canes or ‘stools’ should be planted shallowly, with the upper part of the roots about 5cm (2in) deep on top of the carefully firmed contents of the trench. Any new white cane buds should be just at soil level. Planting deeper than this may discourage the production of new canes. Move the canes slightly as the soil is refilled around them to ensure than no air pockets are left, and then firm the soil carefully with your boot, ensuring that the soil slopes slightly away from the canes. Water well, top with a mulch of compost and cut back the canes (if this hasn’t already been done by the nursery) to just above a bud about 25cm (10in) above soil level.
The spacing of the stools and the distance between adjacent rows depends on the variety (and its vigour) and also on the training system used. For most varieties, the rows should be between 1.2 and 1.5m (4 and 5ft) apart (depending, as much as anything, on the space available) but more vigorous types, especially those with widely arching laterals are better at a spacing of 1.8m (6ft). Spacing within rows for the most popular training method, the English hedgerow system, is 40cm (16in) but there is much to be said for the Scottish stool system where the plants are positioned 70cm (28in) apart.
SUPPORTS AND TRAINING
Like all other cane fruits, raspberries must be supported (although at a pinch, you can manage without support for the shorter-caned black- and purple-fruited and also the autumn-fruiting varieties in non-windy areas). Many support and training systems have been developed in different parts of the world although some are only really relevant to commercial fruit farms. The ones I shall describe here are those that I think are the best for garden use.
The easiest and most straightforward method is with horizontal wires strained between vertical posts. Obviously, any type of stout post can be used but my preference, on the grounds of aesthetics and strength, is for round rustic tannelized wooden posts, sharpened and driven 45 or 60cm (18 or 24in) into the soil (not concreted) to leave a height of about 1.8m (6ft) above ground. For rigidity, the posts should be braced with another diagonal post, driven into the ground and bolted on to the vertical half-way up. Although dependent on the overall size of the fruit garden, a row length of about 3.5m (12ft) between posts is ideal if the wires are not to sag.
Use galvanized or, better, plastic-coated wire of about 10 gauge or 3.15 mm (1/8 in) diameter, suitable for straining — normal tying wire will snap. It can be twisted two or three times around each post or attached to bolts screwed through each post for pulling taut by hand. Alternatively, straining bolts can be fitted at one end to give a tighter pull, although I have seldom found this much use unless completely rigid support posts are used — wooden posts will always ‘give’ slightly as they expand and contract and you will be forever having to re-tension the wires. The wires are most usefully positioned at approximately 60cm and 1.2m (24in and 4ft) above soil level, although this spacing isn’t critical, and with very tall-growing varieties, three wires may be used, the top one at 1.5m (5ft) or even higher. Individual canes should be tied to the wires with soft degradable garden string (fillis) in a figure of eight pattern or alternatively with a single strand running the length of the wire and wound around it, lacing each cane in turn. 1t’s important to use a biodegradable material as you will have pieces of wire or nylon string forever littering the garden after you have retied the canes each year. Raffia is suitable for individual ties but several strands must be twisted together to give adequate strength.
MAIN TRAINING METHODS
There are two main training methods to choose between for a system of single wires. The English hedgerow system is the most popular and here the crop of canes that emerges from and between each stool is thinned and tied-in to the wires so as to give as uniform and narrow a row as possible, the ideal being to have a cane every 10cm (4in). But although this is the most popular system, I have never found it the easiest, partly because it’s difficult to weed between the canes but also because it’s well nigh impossible to ‘arrange’ for them to emerge so uniformly. Much simpler is the Scottish stool system where the canes are allowed to emerge as a group from each stool, excess canes between the stools are cut out, and the canes tied-in, fan-pattern, to the wires.
OTHER TRAINING METHODS
An alternative to the conventional single row is to use a training system that entails having parallel wires.
Here, there are three options.
Half of the canes from each stool are then tied to each wire, the principle being to help separate the fruiting canes from the new ones that grow up in the centre. In the other two methods, two complete sets of posts and parallel wires are erected, just like the single wire system but duplicated. In the simplest, with the wires 60cm (24in) apart, strings are tied across them every 60cm (24in) or so, but the canes are not tied individually, merely confined in groups. There is no fiddly tying-in with this method but it isn’t worthwhile using it in windy areas because the canes inevitably suffer damage through being buffeted. It’s a system that works well with short-caned autumn fruiting raspberries. Finally, with the two sets of wires 1m (3ft) apart there is the Scandinavian system. Here, there are no cross-strings and the fruiting canes are drawn to the side wires and woven around them, also with the objective of leaving the young canes unharmed in the centre.
If space is very limited, as it can be in small gardens, it is perfectly possible to obtain a small crop of raspberries by planting two stools either side of a single post and tying in four or five canes from each of them. Pruning and all aspects of cultivation are similar to more conventional training methods.
PRUNING AND CANE THINNING
You will have gathered from what I have said about training, that the removal of some canes is an important part of raspberry growing. In practice, this is almost all that the1n is to raspberry pruning. In the first year after planting, retain1nnd tie-in all the strong, stout canes that grow and simply cut out any feeble ones or any that emerge too far from the stool to enable them to be tied-in.
These canes will fruit in the following season and once the fruit has been picked, they should be cut off at soil level and then some of the new canes tied in their place. You can easily recognize the new canes: they are shorter, green with fresh healthy leaves, and of course, noor fruit. But here you must be selective. Again, cut (or better, pull from below soil level) any canes too far from the wires, but you must also cut off excess new canes, even if they are fairly strong ones. With most training systems, try to leave no more than eight or nine canes per metre (yard) of row, whether they are evenly spaced, as in the English hedgerow system or fan-patterned, as in the Scottish stool method. With the Worcester system, retain 8 canes per metre (yard) of row nine on each wire).
LIMITING SUCKER GROWTH
Raspberry canes, of course, are simply suckers but we tend to use this name only when we don’t want them. In good growing conditions, masses of suckers can emerge the rows and at some considerable distance from them, causing a nuisance in. They should be hoed or pulled off before they grow more than 15cm (6in) or so tall. You can’t prevent sucker growth but it can be limited by burying heavy gauge plastic sheeting vertically to about 75cm (30in) depth, and about a similar distance either side of the row. If previous experience has been that suckers will be a problem, this might be worthwhile when planting a new fruit garden.
I’ve suggested that the top wire on your post and wire system should be about 11.2m (4ft) high. But of course, many raspberry varieties will grow taller than this, and some a very great deal taller, although these are best avoided for garden use. If the canes are allowed to grow to their full potential, however, the plants will be weakened, yield will be reduced, the fruit at the top will be difficult to pick and, if they are being grown in a fruit cage, the top netting may be damaged. The excess top growth can be pulled down and trained horizontally along the top wire for 25cm (10Oin) or so but any growth beyond that is best cut off.
PRUNING AUTUMN VARIETIES
The pruning of the autumn-fruiting primocane varieties is simpler still. They should be pruned during the second half of the winter by cutting all canes back to soil level. The new canes that bear the fruit will arise within a few weeks so there is never any necessity to distinguish between fruiting and non-fruiting canes.
FEEDING AND WATERING
The simplest feeding procedure is to apply 34g per square metre (1oz per square yard) of potassium sulphate shortly after mid-winter and then 70g per square metre (2oz per square yard) of either Growmore or, blood and bone two months later. On most soils, raspberries display symptoms of iron deficiency — yellowed leaves with conspicuous dark green veins. This can be remedied by routinely applying a proprietary brand of sequestered iron at the manufacturer’s recommended dosage in spring. After the spring feeding, a thick mulch of well rotted manure or compost should be applied while the soil is moist. If the weather is dry, the plants should be watered as the fruit begin to swell; and the soil in the vicinity of the roots shouldn’t be allowed to dry out.
The organic mulch will keep down annual weed growth close to the canes, at least in the early part of the season. If sufficient organic matter is available, it may be spread between the rows but some hoeing is usually still necessary too. The hoe should be used with great care, however, especially on thin soils where most of the raspberry roots will be close to the surface. Perennial weeds among established plants must be controlled with the translocated weedkiller glyphosate as any attempt to dig them out will inevitably damage the canes. Although a total weedkiller, glyphosate may be used quite safely among the crop if it is sprayed carefully on a still day and doesn’t make contact with the raspberry foliage. If necessary, use a piece of cardboard as a temporary shield for the lower leaves on the canes.
Yields vary considerably between varieties and, to some degree, with the training system used, but as a rule of thumb, most modern summer-fruiting types should produce about 1.2-1.5kg per metre (2.4-3 lb per yard) of row; primocane varieties less than half this.
Raspberries should be picked as soon as the fruit parts easily from the core. The maturing period will extend for a month or more within each variety and so several pickings will be needed, even from a single variety. They can, of course, be eaten more or less immediately and will remain fresh in a refrigerator for about two or three days. They can be bottled, made into jams or preserves, or frozen.
Varieties differ in their suitability for preserving.
Unfortunately, raspberries probably suffer from more pests and diseases than any other type of soft fruit. Provided the plants are renewed fairly frequently, however, it is relatively unusual for cropping to be severely reduced.