Summer Pruning of Shrubs in the Flower Garden

New Zealand Journal of Agriculture, Volume 81, Issue 6, 15 December 1950, Page 565

Summer Pruning of Shrubs in the Flower Garden

THOUGH most hardy trees A and shrubs grown in New Zealand for ornament do not require regular pruning, almost all of them require cutting at some time to improve their shape, to make them more healthy, or to increase their flowering capacity and general usefulness. In this month’s article for the flower gardener C. K. Ellis, Horticulturist, Department of Agriculture, Dunedin, gives advice about the pruning of shrubs which flower in spring and early summer on wood matured from the previous season’s growth.

PRUNING of trees and shrubs can be divided roughly into two types: The cutting back and thinning of trees and shrubs which have flowered on matured wood produced during the previous season, and the cutting back of plants which produce their flowers on the tips of shoots of the current season’s growth. The article deals only with the.. first type, which is known as summer pruning.

The most satisfactory guide to the time of pruning is the time of flowering. Spring-flowering and early summer-flowering shrubs should be pruned as soon as the flowers fade. The Diervilla species (weigelias), for instance, will live for a considerable number of years if left unpruned, but their flowering qualities are not nearly as good as those of shrubs pruned regularly and correctly. Immediately after they have • flowered the old flowered shoots should be cut back to a point where strong, new shoots are being produced. The shrubs will not be as long lived when this procedure is adopted, but a brilliant floral display for fewer years is preferable to a mediocre one for many years. ; Jasminum nudiflorum (winter ’ jasmine) is improved greatly by having its flowering shoots cut back to within two or three buds of their bases immediately . flowering has ceased. No cutting must be done on this species after growth has begun for the new season. Syringa species (lilacs) and varieties which do not produce flowers freely are often invigorated by the removal of all suckers from the base, the removal of all weak growths, and the severe thinning of inside shoots during January. Such thinning need be done only every two years or so, but suckers and weak growths should be removed each year. Philadelphus hybrids and their varieties (dwarf mock oranges) of the types similar to P. lemoinei benefit considerably from severe annual pruning. At the end of the flowering period the flowered branches should be cut back to where vigorous new shoots are growing. Such pruning

produces much longer flowering shoots than when the bushes are. left unpruned. The strong-growing Philadelphus species need only an occasional thinning, severe ■ pruning ■ being unnecessary. 1 ’ . The species, and varieties of the genera Cytisus and Genista have a somewhat unusual reaction to pruning. •. Should they be allowed to grow unpruned for several years and then be cut hard back into the old wood, invariably they suffer greatly, and usually they die. 1 If - they are not pruned regularly, they soon become straggly and rather unsightly. Immediately the ‘flowers'.fade the shoots should be cut back, but never beyond the bases of the shoots produced during the previous season’s growth or sections of ' the bushes - are likely to be killed. The following list, though far from complete, may serve as a guide to home gardeners. All the plants mentioned are early-flowering species or Varieties and may be pruned immediately the flowers have faded, but the best pruning time for some of the shrubs listed will have passed. by January. Acanthopanax pentaphyllum (fivefingered . aralia)’ Acer rubrum (red maple) and A. saccharinum (sugar maple): The maples should be pruned only when in full leaf. If they are cut during spring or autumn, the sap flows very freely, to the detriment of the trees. Amelanchier canadensis, A. sanguinea, and A. oblongifolia: Pruning the Amelanchier species is not necessary every year, occasional pruning to retain shape being sufficient.

Ampelopsis heterophylla: Regular pruning is not necessary unless space is restricted, in which case the young growths should be shortened well back once or twice during summer. Further pruning is necessary in winter.

Arctostaphylos manzanita and A. uva-ursi (bearberry): Shaping and cutting out of weak growth every second year is all that is necessary.

Berberis dictyophylla, B. thunbergi (Japanese barberry), B. vulgaris (common barberry), B. darwini, and B. stenophylla: Hedges of Berberis darwini should be clipped hard immediately after they have flowered and should not be cut again until after the next flowering.

Calycanthus fertilis (Carolina allspice): Pruning in alternate years is sufficient.

Caragana arborescens (pea tree) and C. pygmaea: Regular pruning is necessary only in the young stages. Once shapely bushes are obtained occasional cutting is sufficient.

Cercis, siliquastrum (Judas tree): Pruning is necessary while the plants are young, but once they have grown into a good shape only the removal of dead and surplus wood is necessary.

Chaenomeles (Cydonia) japonica (Japanese quince) and C. maulei: When these shrubs are grown as bushes pruning them regularly is not necessary, but when they are grown against walls or trellises they should be pruned back to near the main stems as soon as the flowers fade.

Chimonanthus jragrans (winter sweet): Only occasional pruning to retain good shape is necessary. More flowers are produced if the bushes are left unpruned for several years.

SUMMER PRUNING OF SHRUBS

Chionanthus virginica (fringe tree). Cladrastis lutea (yellow-wood): Annual pruning is not necessary.

Clematis montana and varieties and C. alpina: These two species and several other early-flowering types should not be pruned until after they have flowered. All late summerflowering and autumn-flowering types are pruned in the normal way during winter. . ■ '

Cotoneaster adpressa, C. horizontalis, C. racemiflora, and C. tomentosa: The Cotoneaster species listed need pruning only every 2 or 3 years.

Crataegus coccinea, C. phaenopyrum (Washington thorn), C. crus-galli (cockspur thorn), C. oxyacantha (hawthorn), and C. punctata. :

Daphne ceneorum, D. mezereum, and D. mezereum var. alba: Pruning Daphne species every year is not necessary.

Deutzia gracilis: Gradual renewal by thinning out crowded stems is the best practice. Old flowers and dead and injured wood should be removed regularly.

Elaeagnus angustifolius and E. multiflora: These , are improved if the longest shoots are shortened during summer. . /

Enkianthus perulatus: This species need not be pruned every year.

Erica carnea and E. carnea var. alba: Little more than the removal of flower heads is necessary.

Euonymus alatus and E. europaeus (spindle tree): Only sufficient pruning to keep the bushes shapely is required.

SUMMER PRUNING OF SHRUBS

Exochorda grandiflora (pearl bush). Forsythia intermedia and F. intermedia var. spectabilis: Should this species and its variety be pruned severely, few flowers will be produced the following spring, but if the growths produced are left unpruned, a magnificent display is obtained a year later. Halesia Carolina: Occasional thinning only is necessary. Hamamelis mollis (Chinese witch hazel) . . Kalmia lattfolia. Kerria japonica: As much as possible of the old wood should be pruned out as soon as the flowers fade. Leucothoe catesbaei: Thinning of overcrowded shoots is sufficient. Magnolia denudata, M. lennei, M. soulangeana, and M. stellata: Pruning magnolias regularly is not , necessary, but any thinning needed should be done after they have flowered. If possible, cutting out large limbs should be avoided. Paeonia suffruticosa (tree peony) Little more than the removal of dead tips is necessary. - ' Pieris floribunda, P. japonica, and P. taiwanensis: Little more than the

removal of dead flower heads is necessary. • Prunus maritima (beach plum), P. subhirtella var. pendula (weeping Japanese cherry), P. persica var. flore albo-plena and rubris (double white and red peach), and P. serrulata: Prune flowered shoots back to within three or four buds from the base. Rhodotypos kerrioides (white kerria): Annual pruning is not necessary. Ribes alpinum (mountain currant) , and R. aureum (flowering or Missouri currant) . Sorbus americana (American mountain ash) and S', aucuparia (European mountain ash): Only thinning and shaping are necessary. Stephanandra tanakae: Remove dead wood after growth has started. Parts of this species are almost invariably killed during winter in colder districts. Styrax japonicum. Wistaria sinensis and W. sinensis var. alba: Shorten young shoots back to within five or six buds from their bases in January. Further shortening will be necessary during winter, for the aim is to produce short, spur-like growths. - 1

Flower Garden Work for January

Biennial plants such as wallflowers, sweet williams, and myosotis may be raised from seed sown during January in partly shaded places in the warmer districts. The seedlings should be pricked out a few inches apart in nursery beds where they can develop well and be ready for planting into the borders for next season’s flowering.

Bulb planting will be started in the earlier districts in February, and the gardener should now be considering what types and varieties to buy. The best stocks are always sold rapidly at the beginning of the planting season. If the bulbs have to be stored before being planted they should be kept in a cool and dry place.

Compost, provided it is well matured,, can be. worked into the ground at regular intervals. It is valuable for improving soil texture and the water-holding capacity of the soil. The material should be sieved through a jin. riddle and the coarse parts returned to the heap for further rotting. The fine material, should be spread evenly over the borders and forked in lightly. Chrysanthemums will be growing strongly by January and attention should be given to staking and tying them. As soon as a clump of shoots is well developed a tie should be made right round the plant to prevent the small side branches being blown oft' by winds. Late-flowering varieties should be stopped again by pinching the tips out of the shoots to encourage branching and flowering. Cuttings of a great variety of herbaceous plants and shrubs can be taken in January and rooted in a cold frame or under a bell jar in a shady situation in the open. An inverted glass jar or a box without- top or bottom and with a sheet of glass over it probably serves just as well. The object with soft cuttings is to prevent wilting during the first few days after their insertion in the rooting medium (usually soil), and this is achieved by maintaining high humidity. A few of the. plants which can be propagated in this way are sweet williams, pentstem ons, antirrhinums, hybrid wallflowers, perpetual flowering carnations, and many shrubs, including buddleias, salvias, conifers, . and hydrangeas.

Cyclamen are extremely useful winter-flowering pot plants for the house and are not hard to grow. However, the raising of good plants from seed requires about 18 months, and the home gardener is better advised to buy plants in bloom from a reliable seedsman. After the flowers have faded in spring each plant should be dried off gradually and allowed to rest in a cool place outside until January, when it is started' into growth again by knocking it out of the pot with its ball of soil and repotting it. Most of the old soil should be knocked off and replaced with fresh potting soil. Plenty of crocks in the bottom of the pot ensure good drainage. The corm is . set almost on top of the soil, only its basal part being buried. Flowers of sulphur sprinkled over ' the top of the corm reduce any tendency to rot. The plant should then be watered thoroughly and stood in a cool, shady place until signs of growth appear.

Freesias are excellent pot plants for the house during winter. Eight or ten bulbs can be potted in a 4in. pot in a potting mixture consisting of 7 parts by bulk of loam, 3 parts of peat or leaf mould, and 2 parts of sharp sand. To each bushel of this mixture should be added IJoz. of dried blood, ljoz. of superphosphate, joz. of sulphate of potash, and foz. of carbonate of lime. The pots should be plunged into the soil in a cool part of the garden and watered thoroughly. A covering of ashes or light soil about Tin. deep should be spread over the top of the plunged pots. When the shoots appear above the covering the pots should be removed, cleaned, and taken to a sunny position in the house where the freesias will bloom.

Gaillardias bloom freely and make a bright show, especially in hot, dry weather and in poor soils where few other flowers will flourish. Seed of these plants can be sown in January and the seedlings later transplanted to warm, well-drained, sunny sites in the border. Gaillardias can be multiplied by digging the plants in autumn and cutting the fleshy roots into pieces about 2in. long, the end of the cutting which was nearest the crown being cut off square. The cuttings should be placed upright about 3in. apart in sandy soil with the square ends slightly below the surface of the soil. By spring they will have developed roots and buds and may be transplanted to the borders in the usual way.

Herbaceous perennials in the borders should be staked securely as soon as necessary. The criterion of good staking is a garden undamaged after a gale, yet with few strings and ties showing. Plants with massive and heavy flower heads, such as lilies, will grow unsupported for a considerable time but should be staked securely by the time the flower buds appear.

Hollyhocks can be used effectively near a house to break the lines of bare walls. Plants are best raised from seed sown each year during summer, because young plants are less susceptible to attacks by rust fungi. On an old infected plant the rust spores persist from year to year round the crown at the base. If the typical brown spots of rust appear on the leaves, they should be sprayed at once with a spray containing 2 fl. oz. of lime sulphur and Joz. of colloidal sulphur to 2 gallons of water. Should the plants be near a painted wall, the paintwork should be protected with newspapers or a cloth while the spray is being applied, for sulphur will discolour the paint.

Hydrangeas root readily from cuttings taken from the new shoots at this time of year. Each cutting should be cut off neatly immediately below a bud 3 or 4in. from the

WORK IN THE FLOWER GARDEN

tip and inserted in sand in a cold frame. They should be well watered and covered with a sheet of paper to prevent the entry of bright sunlight, and the atmosphere within the frame should be constantly moist. The bottom few leaves from each cutting may be removed for convenience in handling. Iceland poppies may be planted in January, though recent experience has shown that plantings in February and March are less susceptible to spotted wilt attacks. Seed may be sown in January in boxes kept in a shady position and covered with paper until the seedlings are showing through the soil. As soon as the seedlings are big •enough to be handled they should be pricked out about 2in. apart in boxes .and later planted into a well-limed bed which has not been manured .recently. Plantings made at this time ■of year will flower late next winter. Kniphofias, popularly known as redhot pokers or torch lilies, flower during summer and autumn. They will succeed in comparatively poor soils and dry situations, though most frequently they are planted near pools. They respond well to cultivation and regular dividing every third year. Lawns should be given their quarterly dressing of fertiliser provided the weather is not too dry. If grass growth has ceased because of dryness and the lawns are brown, the feeding should be delayed, as the fertiliser tends to delay recovery of the grasses. The dressing consists of 3 parts of sulphate of ammonia, 1 part of superphosphate, and 1 part of sulphate of iron applied at the rate of loz. per square yard. Meconopsis betonicifolia (the Himalayan blue poppy) thrives in wellshaded places in the cooler parts of New Zealand and makes an attractive summer display among shrubs and trees. The plants should never be allowed to suffer from dryness. The seeds germinate best if sown immediately after ripening, which occurs about January and February. They should be sown .’.n boxes or pots in a shady position and be planted out as soon as the seedlings are large enough.

. . . WORK IN THE FLOWER GARDEN

Peonies are herbaceous plants which normally flower in early summer. They should not be moved more than necessary after they have become established, for they take a season or two to recover, but evergreen clumps which are many years old should be lifted and divided early in the new year, immediately they have finished flowering. Each clump is lifted carefully, the soil is removed, and the fleshy roots are cut into a number of pieces, each with a crown, and replanted. Proteas are excellent decorative plants and should be grown more widely in New Zealand. They are grey-leaved evergreens suitable for well-drained, sunny positions and extremely tolerant of drought. The flowers are conspicuous and. attractive, though not really beautiful. At this time of year the gardener should observe some of the more popular protea species with a view to deciding which he can grow in his own garden. Rambler roses such as Dorothy Perkins which finish flowering before the end of January should also have produced a number of vigorous new shoots from the base of each plant. Branches which have flowered should be cut out and the new shoots be tied in to take their places. Rose blooms should be cut with long stems, as this encourages the growth of new shoots and prevents the bushes from becoming straggly. Faded flowers should be removed by cutting their stems back to the nearest bud 'or strong shoot rather than by removing only the flower head. Rock gardens should be overhauled at this time of year, all dead flower heads and pieces of straggly growth being removed. The full beauty of a rock garden cannot be appreciated if it is not kept tidy. Sweet peas should not be allowed to run wild after their original training in early summer. If dead flower heads are not removed regularly, flowering soon ceases.

Sowings of seeds of annuals for autumn planting may be made in January, including those of winterflowering pansy, Brompton stock, stock Beauty of Nice, cinerarias, and wallflowers. At this time of year flower seeds are best sown in boxes or pots in a cool, shady place and left there until after germination; by this method the seed soil is more easily, kept constantly moist. Topdressing the flower borders with 2-oz.. of sulphate of ammonia and goz. of superphosphate per square yard is very effective if particularly fine , flowers are desired. This dressing should not be given if good dressings of flower border fertilisers were applied during spring. Violas and pansies will have grown straggly by January and - will be exhausted by continuous flowering. The plants should be cut back to within an inch or two of the ground to encourage them to . send up new shoots, which probably will provide valuable flowers during autumn. A few plants may be left to provide cuttings which later can be rooted in the cold frame. Pests and Diseases Narcissus fly: Cultivating the soil thoroughly where bulb foliage has died down does much to reduce the possibility of attack from narcissus fly by making it difficult for the young larvae to find their way to the bulbs. When narcissus bulbs have been lifted they should not be left lying about the garden, as this provides opportunity for the flies to lay their eggs directly on them. All bulbs that feel soft should be destroyed by burning, as they are probably infected. Rose mildew is probably the commonest disease of roses in New Zealand. Its attacks are particularly severe where circulation of air about the plants is poor; for example, about rambler roses growing against a wall. This disease can be controlled reasonably well by regular dusting with

Grevillea rosmarinifolia

interesting Australian evergreen shrub, Crevillea rosmarinifolia, as the name suggests, has rosemary-like foliage and clusters of rich red flowers borne during summer. It is of a bushy habit and grows from 4 to 7ft. high and almost as much in diameter.

The grevilleas prefer a lime-free soil and make splendid subjects, particularly for seaside gardens. The best medium for growth is a sandy loam to which plenty of peat or leaf mould has been added. Pruning, which may be done after flowering has finished, is carried out mainly when the shape of the bush is in need of attention.

The plants may be propagated by cuttings to 2in. long taken from side shoots, with or without small heels of old wood attached, and inserted in sandy compost in a glasshouse or glasscovered frame, box, or pot in January or February. Layering the ends of the lower branches in spring is a method sometimes used. —H. P. THOMAS, Vegetable Instructor, Department of Agriculture, Wanganui.

flowers of sulphur. A convenient method of dusting is to place some flowers of sulphur in a small bag made of fine muslin, hold the bag close to the plants, and tap it sharply with a stick, causing clouds of sulphur dust which reach most parts of the plant.

Thrips are slender insects up to Jin. long and varying in colour from yellow to black. Their attacks are particularly ■ severe on gladiolus. Regular spraying with nicotine sulphate (1 part in 800) plus summer spraying oil (1 part in 100) usually controls this pest. D.D.T. dust is also effective. Caterpillars of the magpie moth (“woolly bears”) attack cineraria leaves at this time of year, looper caterpillars eat geraniums and other plants, and leaf roller caterpillars become common. They can all be controlled by hand picking and by dusting with derris or D.D.T. dust. Geranium rust, which disfigures geranium plants, by producing rustbrown spots on the leaves, can be controlled by regular spraying with 2 fl. oz. of lime sulphur and J fl. oz. of colloidal sulphur to 2 gallons of water.

Greenflies are still common in January and should be sprayed at 10-day intervals with nicotine sulphate at the rate of 1 fl. oz. to 4 gallons of water plus 6 fl. oz. of summer spraying oil until all trace of the pest has disappeared. Subterranean grass caterpillars, larvae of the large nocturnal porina moth, often ruin lawns by eating the grass and leaving large bare patches during summer. Poison baits have been found most effective in controlling this pest; 21b. of wheat bran, mixed thoroughly with 2oz. of arsenate of lead powder or loz. of paris green moistened slightly, makes sufficient to broadcast over 1500 sq. ft. The application should be made on a fine, warm evening. Both arsenate of lead and paris green are extremely poisonous substances and the greatest care should be exercised in using them, especially where there are children or pets. The treatment can be repeated during February if the attack is serious. An alternative to the laying of baits is spraying with arsenate of lead at the rate of 31b. of paste or l|lb. of powder per 100 gallons of water.