How to Grow Carnations
It is impossible to say when the culture of carnations began. They have been esteemed and cultivated in Europe for many centuries, but there is no record of their introduction to Great Britain. The story that they came over with William the Conqueror lacks evidence, but could be true. Judging from old paintings, it seems that for many centuries they differed little from their wild ancestor, Dianthus caryophyllus, a native of south and west France. When they began to vary from the wild type is not known, but it is certain that thehad reached a high degree of perfection early in the 19th century.
Three principal types of carnation are now grown: the border and the perpetual-flowering carnation, both of which are described in detail below, and the marguerite or Chabaud carnation, which is grown from seed. Marguerite carnations make splendid bedding plants, but their blooms are much inferior to those of the other two kinds. Their culture is the same as that of half-hardy annuals, and they are therefore not further described here.
Unfortunately, inferior plants of all types of carnation are frequently sold, and sometimes it even happens that plants sold as border or perpetual-flowering carnations turn out to be marguerite carnations. There are, however, a number of absolutely reliable specialist firms, and it is best to buy from them.
Carnations of more or less pure descent from the wild species are known as border carnations, and good specimens have a perfection of form and colouring found in few other plants.
The flower is of symmetrical shape, with broad, smooth-edged petals, and there are certain technical terms used to describe the types of colour marking.
Flowers of a single, even colour are called selfs.
In other cases, the basic colour is called the ground, and this may be marked in various ways. Where the markings are irregular or the colours blend, the flowers are called fancies. Picotees have a ground colour of white, yellow or buff, and the marking is confined to a band, which may be broad or narrow, round the edge of the petal. Those that have radial stripes or wedge-shaped marks are called flakes if the marks are of one colour only, and bizarres if the marks are of more than one colour.
The border carnation is a hardy perennial, producing in its first year a single flowering stem, which bears several flowers about July. Two-year-old plants will have a mass of bloom on several stems. Although some people keep plants for a third or fourth year, it is better to replant after two years.
SITE AND ASPECT
It is essential that the border carnation has a winter rest, and therefore it does not grow properly in countries where the winter is too mild.
Exhibitors often grow border carnations under glass, and indeed some varieties are suitable only for this purpose, but this is done merely to control watering and to protect the blooms. The plants are completely hardy and the greenhouse does not require heating.
Border carnations need a sunny position in an open place where the air can circulate freely; they should not be sheltered by other plants. They are highly resistant to many chemicals and grow particularly well in the smoky atmosphere of industrial areas. They also resist salt spray better than most plants, so they do well near the sea, and they thrive in chalk soils.
They are intolerant of stagnant moisture, and need good. Where there is any doubt about drainage it is advisable to raise the bed 6 in. or so to ensure success, because the plants are surface-rooting.
PREPARING THE SOIL
Border carnations will grow in most soils, provided they are not acid. If a simpletest shows that the soil is acid, add carbonate of lime at 8 oz. to the sq. yd. after digging.
Periodic checks should be made, particularly in industrial areas, for there the rain is usually acid and leaches out the lime remarkably quickly. If necessary, carbonate of lime at 2 oz. to the sq. yd. can be applied to the soil while the plants are growing.
Provided the sub-soil is porous, deep digging is not needed, turning to a depth of 9 in. being sufficient.
Well-rotted stable manure or compost is beneficial if buried below the top spit. Peat and leaf mould should be avoided except by experts, for after a time they tend to make the soil acid.
Wood or bonfire ash, at up to 8 oz. to the sq. yd., and soot that has been stored for at least three months, at up to 4 oz. to the sq. yd., are particularly beneficial if hoed into the top 4 to 6 in. of soil after digging. Bone meal should also be used, at 4 oz. to the sq. yd.
After preparing the bed, allow it to settle for a month or so and water it well unless there is plenty of rain. Autumn is the best time for planting, but spring is almost as good. Young plants that have been grown in 3-1/2 in. pots are usually sent out by garden centres or nurseries. The root ball and the soil round the plants should be thoroughly moist before planting.
Put the plants in about 15 in. apart, planting firmly but not deeply. It is very important that no more of the stem than is absolutely necessary should be below soil level; in no case should the base of any leaves be buried. Deep planting invites stem rot, and the temptation to plant deeply to keep the plants upright should be resisted. Support can be given by a short stick and a ring tie.
In winter it is only necessary to firm in young plants if they become loosened by frost; to ensure that all plants are secure enough not to be broken by strong gales, and that no leaves or other rubbish collect round the main stems.
As the soil dries in spring, remove weeds by shallow hoeing, not more than 1 in. deep. Larger weeds should be removed by hand, for border carnations have shallow roots, and can be ruined by deep, vigorous hoeing.
If the soil has been properly prepared, young plants will not need spring feeding, but if it has not, and as a treatment for older plants in any case, apply special carnation fertilizer carefully following the manufacturer’s instructions. Ordinary garden fertilizers usually have too high a proportion of nitrogen for carnations; this leads to large, sappy growth, which will make the plants prone to disease, and it may also cause the calyces of the blooms to split. Never use organic mulches, for they rot the stem.
Border carnations are fairly resistant to drought, but if there is a long dry spell, give them a good soaking of water at the rate of at least 5 gal. to the sq. yd.
STAKING AND DISBUDDING
As soon as the flower stems begin to grow, insert a thin 3-ft. Bamboo cane close to each stem, and secure the young shoot to it with a ring tie, which can be moved upward as the stem grows.
It is most important that the growing tip should not be broken, and border carnations should therefore never be stopped.
The main stem usually carries numerous side stems, and the plant should be disbudded until one bud is left at the top of the main stem and one at the end of each side stem. Disbudding should not be too early or too vigorous; the buds should be removed when about the size of a pea. The top or crown bud opens first, sometime in July, and the side buds follow in succession.
Cuttings of border carnations are difficult to root except in a mist propagator; the usual method of increase is by.
Do not layer more shoots than are required, because each layer robs the parent plant of a flower stem the next year. One-year-old plants provide the best layers.
To form a rooting medium, stir into the soil round the plant a mixture of two parts by bulk of peat, one part sharp sand and preferably half a part of vermiculite. The mixture should be moist. (Peat can safely be used here, because it does not remain long enough to acidify the soil.) When flowering is over, layer the carnations in accordance with the instructions given in Propagation.
Growing from Seed
Border carnations do not come true from seed, and there is great variation in the flowers of seedlings, most of them being inferior to named varieties. Very good blooms can, however, be obtained from good seed sold by specialist nurserymen, and there is always a remote chance of producing an outstanding seedling that can later be propagated by layers to form a new variety. Seedlings are often very vigorous, and make a splendid show in their second year.
Seeds are best sown in boxes in April or May, using the John Innes seed compost. Cover the seeds with not more than 3/4 in. of soil; at a temperature of 55 to 70° F. (13 to 21° C), germination will take place in seven to ten days. Pricking and planting out are the same as for any hardy perennial.
PESTS AND DISEASES
Carnations are seldom attacked by pests, and such common ones as greenfly and caterpillar can be curbed if the usual insecticides are applied.
Cuckoo spit or soapy blight is serious on carnations, and can be cured by using any usual insecticide in sufficient quantity to wash off the froth. Maggots sometimes bore into the stems in winter, but this can be forestalled by spraying the plants every ten days or so during the autumn with a repellent insecticide such as B.H.C. White spots on the blooms of dark varieties, caused by thrips, can be prevented by applying D.D.T. or B.H.C. To the buds.
Stem rot, due to bad drainage or over-deep planting, is serious. The plants should be destroyed, the drainage of the bed improved and new plants put in at the proper depth. Rust, appearing as pustules of brown powder on the leaves in autumn, is a nuisance but not fatal. As soon as the disease appears, use a sulphur spray, according to the maker’s instructions, on all plants, whether they are affected or not.