Green light for blueberries

Press, 28 February 1980, Page 12

Green light for blueberries

GARDENER’S DIARY

By

Derrick Rooney

Why, asks a reader, are blueberry bushes so expensive, and can they be grown successfully in Canterbury — two questions to which it is not easy to give anything but partial answers. First, they are expensive partly because there are certain difficulties in propagating them (though there are methods, that the amateur can use), and partly because they are new to this country' and the consumer, subject to the ancient laws of the market place, is paying through the nose for novelty. To the second question, the answer is a qualified “Yes” — as long as they are not limed, and prefera--bly not fed with artificial fertilisers. They are plants that grow naturally in soils of low fertility. Most of the blueberries in cultivation in New Zealand are hybrids, either man-made or, more often, selected from wild-col-lected plants. The taxonomy of these plants seems to be ill-de-fined; some authorities lump them together as two or three large polymorphic species, others recognise eight to 10 species and numerous geographic forms and subSDPCIPS But as far as the home grower is concerned, a more practical division is into low-oush types, which are bog plants and seldom, if ever exceed a height of 18 inches and the highbush varieties, which, will grow six to 15 feet high. Blueberries belong to the genus vaccinium, as do the true cranberries, and thus are trans-Atlantic first cousins of the bilberry and whortleberry, which are British and Northern European species of the same genus. There are Asiatic species, too. All belong to the great family of Ericaceae — the heather family, a vast group that includes heaths, heathers,- the strawberry tree, and most notably the rhododendrons. '

In New Zealand, the family is represented by a handful of species of gaultheria and perhettya, the snowberries. /Almost'' without exception the members of this family occur in acid soils, often’■ rather sandy, and always with a. high organic content, either in the form of humus or peat but rarely as animal manure.

It is this soil preference that makes the blueberry tricky to grow. Though they are to be found over a vast area of the North American continent they are.very fussy about sites. The low-bush blueberries are, frequently, true bog plants, growing only a foot or so high. They inhabit the more northerly latitudes; the high-bush blueberries tend to be more southerly, and thus more tolerant of hot summer weather. But

they, too, are moisture lovers, and lime is anathema to them.

Many come from areas known in the United States as “pine barrens”; swampy pine forests, perhaps not unlike bur own kahikatea forests but without the dense undergrowth — areas rich in wildflowers but low in economic value.

The soil in these parts is often sandy, but because -there is an impervious laver beneath, it remains waterlogged, and in these conditions the accumulated organic debris turns into peat rather than

humus. So the blueberries that come from such places need rather more -than the normal Canterbury summer rainfall. According to the R.H.S. “Dictionary of Gardening,” the ideal growing situation for blueberries is an acid, sandy loam with a summer water-table that rarely dfops below 8 inches.

It is not difficult to create -these conditions artificially on a small scale — as many iris and primula fanciers do to grow • the choice, moisture-loving species — by simply burying a sheet of thick polythene about 18 inches below ground. Fortunately, the hybrid blueberries available now in this country seem to have sufficient vigour -to survive, and grow, without this special treatment. Two young plants in my, garden have done quite well this year, despite late planting, a site that is not altogether favourable because neighbouring trees tend to rob it of - food and moisture, and an attack by chickens.

But it has been a cool, wet summer, without the expected prolonged nor’west spells, and it remains to be seen how they will cope with a normal season.

One of the problems with blueberries, and one of the reasons why blueberry bushes are expensive to buy (though it does not explain the ridiculously high . prices sometimes asked), is that they prefer to grow, in cool Weather, and whereas many shrubs can be multiplied rapidly by softwood cuttings in summer, blueberries do not root readily from summer cuttings because ’the temperature is usually too high.

But there are two methods by which the amateur can multiply his blueberry bushes Once he has them. They were described as long ago as 1891 in. Bailey’s “NUrsery-Man-ual,” a very useful little reference book that stayed in print until the 19405.

One method is a rather drastic process known as “stumping,” in which the whole bush is cut down to the ground while dormant, in winter. The stump is then covered several inches deep with a mixture of one part sand and two parts peat, and kept moist throughout spring and summer.

According to Bailey, the new growths from the stump take the form of erect, scaly rootstocks which continue into leafy stems. They “tend to develop roots in profusion,” and may be removed from the stump early in the next spring. The' top growths are shortened to about two inches, and the rooted pieces are set out’ in a peaty soil to grow on through the summer, preferably in a-well-ventilated, shaded frame. By the autumn, they. should make sturdy little bushes.

The basis of this method of propagation lies in the art of deception — in hoodwinking the plant into producing small sprouts in such a way that their basal parts are, in effect, scaly rootstocks, with a strong tendency to grow fibrous roots. The same principle applies to Bailey’s other method, which he calls “tubering.” Cuttings are taken in autumn of old,

hardened wood from vigorous bushes, grown in full sun to ensure that the wood is starchy and well ripened. The cuttings, 3in or 4in long and unbranched, are packed in clean hardwood sawdust or sphagnum moss and refrigerated for two months or longer, during which time their starch is converted to sugar.

Early in spring, before buds begin to swell, the cuttings are taken out of refrigeration and planted, on their sides, in a mixture of peat and hardwood sawdust (Bailey says basswood sawdust is best, maple or birch next best; pine is “too acrid”). The easiest way to do' this is to lay the cuttings out horizontally, then cover them to a depth of about one inch. NOw comes the tricky part; the frame must be kept closed to retain high humidity, but the temperature inside it must not rise above 17 degrees. Sprouts should grow from each cutting, and as spring and summer progress these should root at the base. Bailey suggests leaving them in the cut-

ting-frame until the next spring, by which time they should be ready for planting, out in nursery beds.

Root cuttings, says Bailey, may be used instead of stem cuttings, “and often make excellent plants.” He recommends a mixture of four parts sawdust to one part of peat. These are the only methods, other than seed, that I know by which the amateur grower can raise his own young blueberries. Propagation by cuttings, taken in autumn, is possible, but not practicable for the amateur because the cuttings must be kept at ,-a steady 13 to 18 degrees for a month, then at a night temperature of 2'degrees and a day temperature of 15 degrees for two month's, and then at a night temperature of 13 degrees and a day temperature of 15 degrees indefinitely, until the appearance of twiggy secondary growths indicates that the cuttings have rooted. All this time the air inside the glasshouse must be kept saturated with moisture.