This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
Dahlias are offered in five forms: large clumps, ordinary field-roots, pot-roots, green plants and seeds. The clumps give the best satisfaction the first year, but are entirely too large and unwieldy for anything but a local trade and exchange among amateurs. The ordinary field-roots are the most valuable, as they can be handled easily and safely, and always give satisfactory results. Pot-roots are largely used in the mailing trade, and, while they will not give as good results the first year, are valuable for shipping long distances where larger roots could not be profitably used, owing to heavy transportation charges. Green plants are mainly used to make up any deficiency in the field-crops, owing to unfavorable seasons, or an unusual demand for certain varieties.
There is diversity of opinion as to the proper time to plant dahlias, but the writer has always found it best to plant early, and would advise planting large strong roots about two weeks before danger of frost is over. This would be, in the vicinity of Philadelphia, about April 15; and as it requires from two to three weeks for the plants to get up through the ground, there will be no danger, while the plants will bloom that much earlier. It is best, however, not to plant small roots or green plants until danger of frost is over-in the vicinity of Philadelphia, about May 1 to 10, according to the season. A good rule to follow everywhere would be to plant small roots and green plants as soon as danger of frost is past, and large roots about three weeks earlier.
The first requisite of successful garden cultivation is thoroughly to stir the soil to considerable depth and enrich it, if it is not already rich, by broad-casting and plowing or spading in a good coat of well-rotted manure. Too much stress cannot be placed upon the thorough preparation of the land, as it not only allows the roots to go down deep after the moisture more readily during dry weather, but affords good drainage during excessive rains. Having prepared the land as above, mark out rows 4 feet apart and 6 to 8 inches deep, and plant the roots from 18 inches to 3 feet apart in the row, according as solid rows or specimen plants are desired.
In its early stage of development, the dahlia grows very rapidly, and should be kept thoroughly tilled. But while deep tillage is beneficial during its early stages of development, it is almost fatal to the production of flowers if practised after the plants come into bloom. Therefore, when the plants begin to bloom, cease deep tillage, and stir the soil to the depth of 1 to 3 inches only, but stir it often, and never allow the surface to become hard and baked. This will not only prevent excessive evaporation of moisture and keep the under soil cool and moist, but will also prevent the destruction of immense quantities of feeding-roots.
As long as the roots supply more nourishment than is needed to support the plant, both the plant and the flowers increase in size and beauty; but as the supply gradually becomes exhausted, the plants cease growing and the flowers become much smaller. This condition is what is generally called "bloomed out," but what is really "starved out," and can easily be prevented if the proper attention is given to the plants. As soon as the flowers begin to grow smaller, broadcast around each plant a small handful of pure bone-meal, and nitrate of soda, in proportion of four parts bone to one part soda, and carefully work it into the soil.
This is a debatable subject, and, although a judicious application of water during a severe dry spell is very beneficial, yet in nine cases out of every ten in which water is applied, a thorough stirring of the surface soil would give better results.
Many persons think Dahlias should be watered every evening, and as soon as they are up begin watering them daily unless it rains. This practice is very injurious, as it causes a rapid but soft growth, and as the soil is seldom stirred, the roots become so enfeebled that they are unable to supply the needs of the plant; as a consequence, but few buds are formed, and they generally blast before developing into flowers. In other cases, as the enthusiasm wears off, watering is stopped, probably right at the beginning of a severe drought, and the weak, pampered plants are fortunate to survive, much less bloom.
Fig. 1215. A semi-double form of dahlia.
If large, strong roots are planted and the soil is kept thoroughly stirred, there will be little need of artificial watering until after the plants come out in full bloom. However, if it should become hot and dry after the dahlias come into bloom, it would be very beneficial to give them a thorough watering once each week or ten days during the continuance of the drought. But care should be taken to stir the soil to the depth of 1 to 2 inches the next day, carefully pulverizing it later in order to break the natural capillarity by which the moisture is evaporated.
The best rule to follow is not to allow the plants to suffer for want of moisture, not to water them except when they need it, but to water them thoroughly when necessary, and not to allow excessive evaporation for want of frequent stirring of the soil.
In planting the roots or tubers, place them on their sides with the eye as near the bottom as possible, and cover only 2 to 3 inches deep. As soon as the shoots appear, remove all but the strongest one, and pinch out the center of that one as soon as two or three pairs of leaves have formed, thus forcing it to branch below the level of the ground. As the plants develop, the soil is filled in gradually by subsequent hoeings. By this method the entire strength of the root and the soil is concentrated on the one shoot, causing it to grow vigorously; while the pinching back not only causes it to branch below the surface of the soil, and thus brace it against all storms, but also removes all of those imperfect, short-stemmed flowers that appear on some varieties. If the plants are pinched back low, as described, there is no danger of the branches splitting down, as the soil around them will hold them securely in place. However, when they branch above ground and are inclined to split down, drive a short stout stake near the stem and tie the branches to it.
These short stakes are not to hold the plants up, but to prevent the branches splitting down when the above directions have not been followed closely.
By this method it is possible to grow dahlia blooms on stems from 18 inches to 2 feet long. It has always been thought necessary to tie dahlias to stakes to prevent them from being blown down by heavy winds. The system of staking is not only unsightly during the early stage of their growth, but is attended with considerable labor and expense. Staking, however, is unnecessary, if the directions already given are followed, as the plants will branch out below the surface of the ground, and the stems will become so heavy as to resist the strongest winds. The plants are one-third dwarfer, compact and regular in form, and produce much finer flowers on long stems well supplied with buds and foliage.
As soon as the plants are killed by frost, lift the roots, and, after removing all the soil possible from them, allow them to dry in the air for a few hours, when they should be stored in the cellar or some other cool place secure from frost. If the cellar is very dry or is not frostproof, put the roots in a barrel or box and cover completely with dry sand or some other suitable and convenient material, such as sawdust or tanbark, to prevent freezing or loss of vitality by drying or shriveling. Lawrence K. Peacock.