DAHLIA: FULL DETAILS OF CULTIVATION
For Garden Display and Cutting Throughout Summer and Fall
A tender, tuberous-rooted summer-and autumn-flowering plant which is found wild in Mexico. It belongs to the Daisy family, Compositae, and commemorates Dr. Dahl, a Swedish botanist.
Among late summer and autumn flowers the Dahlia is a worthy rival of the Chrysanthemum in popular favor, which is not surprising when one considers its many virtues. In coloring it embraces every conceivable shade and combination of shades with the exception of blue. The modern varieties have lost the old habit of hiding their blooms among their foliage; this has now been bred out of them, even in the true Cactus type, so that they now carry their flowers well above the leaves on strong stems for all to see. They prefer an open, sunny position, but nevertheless grow well and flower freely in partial shade. If given reasonable attention, particularly in regard to removing dead flowers, they bloom with remarkable prodigality from August until frost puts an end to their display; and, provided they are adequately supplied with food and moisture, they are among the easiest of all garden plants to grow successfully.
Where to Grow Them. Dahlias are such accommodating plants that it is never difficult to find room for at least a few of them, even in the smallest garden. The dwarf kinds are valuable for filling formal flower beds, for these Dahlias, of the Coltness Gem type, start blooming in early summer and continue without a break until frost if the dead flowers are picked off regularly each week, and spent growths are cut back. Other types specially suited for use in formal bedding are the dwarf double-flowered bedding Dahlias, and the miniature peony-flowered varieties of the Bishop of Llandaff type.
Borders of Dahlias. In large gardens a spectacular effect can be achieved by devoting a whole border to Dahlias. The best result is achieved by grading the varieties according to height, and by planting groups of not less than three plants of each variety. Such a border can contain representative selections of all the principal types, with the dwarf bedding varieties at the front, giving place to the small and medium Decorative and Cactus Dahlias, backed by large Decorative and Cactus varieties.
Dahlias are invaluable also for planting in the mixed flower border, and for filling gaps in the herbaceous border, for which purpose priority should, perhaps, be given to the smalland medium-flowered type, both Decorative and Cactus, as these are the best of all for general garden display, and they include also the best for cutting, though for the latter purpose the charming Pompon Dahlias must also be considered.
Official Dahlia Classifications.
Size divisions of Dahlias: The various types are recognized in three general size groups, i.e., "A" or Large, over 8 in. in diameter; "B" or Medium, 4 to 8 in. in diameter; and "M" or Miniature, under 4 in. in diameter. The exception to the above size groups are the Pompons, which must be under 2 in. and Miniature Ball Dahlias, 2 to 4 in. in diameter.
Formation or Type Classifications. Single Dahlias: open-centered flowers, with only one row of ray florets, with the margins flat or nearly so, regardless of the number of florets.
Mignon Dahlias: single flowers, the plants approximately 18 in. in height.
Orchid-flowering Dahlias: flowers as in Single Dahlias excepting that the rays are more or less tubular by the involution of the margins.
Anemone Dahlias: open-centered flowers, with only one row of ray florets, regardless of form or number of the florets, with the tubular disc florets elongated, forming a pincushion effect.
Collarette Dahlias: open-centered flowers, with only one row of ray florets, with the addition of
one or more rows of shorter, petal-like florets, usually of a different color, forming a collar around the disc.
Peony Dahlias: open-centered flowers with two to five rows of ray florets with or without the addition of smaller curled or twisted floral rays around the disc.
Incurved Cactus Dahlias: fully double flowers with the margins of the majority of the floral rays fully revolute for one half or more of their length and the tips of the rays curving toward the center of the flower.
Straight Cactus Dahlias: fully double flowers, with the margins of the majority of the floral rays fully revolute half their length or more, the rays being straight, slightly incurved or recurved.
Semi-Cactus Dahlias: fully double flowers, with the margins of the majority of the floral rays fully revolute for less than half their length and the rays broad below.
Formal Decorative Dahlias: fully double flowers, with the margins of the floral rays slightly or not at all revolute, the rays generally broad, either pointed or rounded at tips, with outer rays tending to recurve and central rays tending to be cupped, and the majority of all floral rays in a regular arrangement.
Informal Decorative Dahlias: fully double flowers, with the margins of the majority of the floral rays slightly or not at all revolute, the rays generally long, twisted or pointed and usually irregular in arrangement. Ball Dahlias: fully double flowers, ball-shaped or slightly flattened, floral rays blunt or round at tips and quilled or with margins involute for more than half the length of the ray in spiral arrangement, the flowers 4 in. or more in diameter.
Miniature Dahlias: all Dahlias which normally produce flowers that do not exceed 4 in. in diameter, pompons excluded, to be classified according to the foregoing descriptions.
Pompon Dahlias: having same characteristics as Ball Dahlias, but, for show purposes, not more than 2 in. in diameter.
Dwarf Dahlias: a term that applies to plant size without regard to the characteristics of the bloom.
Preparing the Soil. Although elaborate preparation of the soil is unnecessary, there is no doubt that Dahlias do appreciate an ample supply of food and plenty of moisture. These needs are best met by digging in plenty of humus-forming material well in advance of planting. Light soils should have half-rotted organic matter forked into the lower soil and a generous quantity of compost, together with 3 oz. of bone meal to the square yard, mixed into the topsoil. Failing sufficient compost, or even in addition to compost, a dressing of peat moss can be applied with advantage. If the soil is very clayey or is acid, the addition of hydrated lime will improve it to the Dahlias' liking.
Propagation. Dahlias can be increased by sowing seeds, taking cuttings and by dividing the tuberous roots.
If the tubers are taken from winter storage in February or early March, placed in flats, partly covered with leafy soil and kept moist, they soon start into growth in a greenhouse having a temperature of 55-60 degrees. When the young shoots are about 3 in. long, they should be cut off, each with a small piece of old stem attached, and inserted as cuttings in a bed of sand or vermiculite. If the atmosphere around them is kept moist they will form roots in a few weeks. When rooted they should be placed on the benches of the greenhouse and soon afterwards be repotted in 4-in. pots. They must be hardened in a cold frame prior to planting them out of doors in early June.
Sowing Dahlia Seeds. Seeds of Dahlias are sown in a heated greenhouse, temperature 55-60 degrees, in February in flats of sifted sandy loam. The flats are covered with glass and then with paper to keep the soil moist and the temperature fairly constant. As soon as the seedlings are an inch or two high, they are potted singly in
small pots in a compost of loam and leaf mold. When well rooted in the small pots they should be repotted. Later they should be hardened prior to planting out early in June.
The single-flowered Mignon and other single and semidouble dwarf types can be raised in this way without difficulty. They make good plants by summer and bloom from late in June or early July until autumn.
When to Plant. The young growths of Dahlias are frost-tender; therefore, it is unwise to plant them in the open ground until all risk of frost damage is past. In practice this means that young Dahlias from cuttings and plants raised from seed should not be set in the open ground until the end of May or early in June, according to district.
Planting Old Tubers. It is usually safe to plant divisions of old Dahlia tubers that have been stored for the winter directly into the open ground about the time the first Corn is sown, setting them with the tops of the tubers about 4 in. deep.
When dividing clumps of Dahlia tubers it is very important to remember that the new growth is produced from the base of the old stems, not from the actual tubers, so that it is essential to secure a portion of old stem with each division. The safest method is to start the tubers into growth first in flats of leaf mold or moist peat in a completely frostproof place. Once the new shoots are showing, the tubers can be carefully divided with a sharp knife, the cut surface being dusted with flowers of sulphur or powdered lime to prevent decay.
Planting Young Dahlias. All young Dahlia plants should be thoroughly hardened by gradually exposing them to outdoor conditions, before they are set in the open ground. Those of medium to tall height will need stout stakes to support them, for they become very top-heavy as growth advances and unless secure may be blown over by strong winds. Although they may look rather unsightly, it is best to put the stakes in at planting time, before the plants or tubers are actually set in place, so as to avoid any damage to the roots. The stakes should equal the flowering heights of the varieties.
If three plants of each variety are grown, they are most effective when set in triangles, spacing them 18 in. to 3 ft. apart, according to the height they will attain, and allowing a similar distance between the groups. The dwarf single bedding Dahlias should be spaced 12 to 15 in. apart. The plants should be put in with a trowel and the soil made firm about them, after which they should be watered well if the weather is dry.
Treatment After Planting. Each plant should be tied to its stake immediately after planting. When growth is active again the growing tips should be removed, just above the third pair of leaves, to encourage the development of side shoots, which should be looped to the stake as they lengthen, at the same time removing any weak, spindly ones. Thereafter, growth will be rapid, especially if the plants are kept well watered and given occasional soakings of weak liquid fertilizer. Mulchings of old manure, compost, or even lawn mowings, will benefit them; in fact, the chief aim should be to prevent any check to the roots through dryness.
Some thinning of the growth may be desirable as the plants gain size, and if flower buds are produced prematurely these should be removed; in fact, apart from the dwarf bedding types, if they are to give a really good show they should not be allowed to bloom until they have gained at least two thirds of their height.
Dahlias for Exhibition. No show flower is easier to grow than the Dahlia, and even the large Decoratives are not beyond the range of the skilled amateur. The aim should be to keep the plants growing strongly, by heavy watering (not driblets) when necessary. Growth thinning should be rather more drastic than for garden display, and later the number of flowers must be restricted by disbudding, especially on the big bloom types. Timing of the latter is probably the most difficult part of the business, though easy to master by experience; big blooms take 3-4 weeks, or rather less in hot weather, to reach full beauty, and this can be controlled to a limited extent by shading.
Lifting and Storing the Tubers. When the first sharp frost has cut down the plants, the tubers should be lifted without delay. If they are exposed to further severe frosts, it is possible that they will be damaged although the damage may not be apparent until some time afterwards.
The ideal place for storing them is on an earthen floor in a cool, frostproof cellar. If such a position is out of the question the tubers may be placed in boxes in a frostproof place. The storage temperature should be between 35 and 50 degrees. In heated cellars where the air is dry, cover the tubers with peat moss, sand, ashes or vermiculite; or wrap them in newspapers to prevent shriveling. Cut broken tubers cleanly across and dust cut surfaces with fine sulphur. Examine tubers in storage occasionally through the winter.
Storing Dahlias Out of Doors. Some gardeners find that Dahlia tubers remain sound if they are buried out of doors. A hole 2 ft. or so deep, and as wide as may be necessary, is dug, and ashes, straw or salt hay are put in the bottom. The Dahlia tubers are then put in, stout sticks are set across the top of the hole, and straw and finally soil are heaped on to make a frost proof covering.