Delphiniums can easily be grown from seeds that can be sown practically any time of the year, according to the climatic conditions, equipment available, or desired flowering time.
Under California conditions, for early spring flowers, sow from June to September; for midsummer blooms, December to January; and for Fall blooms, February to April.
Early Seed Sowing
Early summer sowing is recommended in regions with severe winters so the little plants are well-established before the winter sets in.
Otherwise, the most practical time to sow is early spring. Seed can be kept in good condition for several years if kept in airtight containers in a refrigerator.
It is practicable, even with fresh seed, to place it between two moist blotting papers and leave it directly under the freezing compartment of the refrigerator for at least a week to induce higher germination.
For best results, sow in flats in a mixture of two-thirds coarse leaf mold and one-third loam, covering slightly with the same mixture, and moisten thoroughly.
To prevent evaporation, cover the flats with newspaper and glass until germination occurs.
Immediately after the young plants begin to appear, both the glass and the newspaper should be taken off; however, the plants should be kept shaded and moist constantly.
Germination
If the seeds do not germinate 100% percent and the flats are exposed to strong light immediately after the first few plants have appeared, the rest may not germinate at all.
Artificial heat can be used for germination in early spring, giving far better results than the natural heat in summer.
Bottom heat is necessary to get the best results in germination, with a cool temperature overhead.
This is well supplied under glass in the early spring; however, in summer, it is usually the opposite due to hot weather conditions, and this is why many people have failed even with the freshest seed.
At temperatures of 85° degrees Fahrenheit and up, the germination is often very poor, and what germinates stands a very good chance of being simply cooked.
To prevent this, after the seeds are sown in flats, place them on the floor in a cool room or shed, where they can be kept dark for the first 10 days until germination takes place. Then give light and fresh air, but keep them well-protected against any drying out.
We have repeatedly checked on seeds that were sown under greenhouse conditions in Summer or the cool shed method or a well-shaded lath house, and the results in each case were from 20% to 50% percent better under lath house conditions than under the greenhouse conditions.
Under slow, cool germination, practically every seed will gradually come up. However, under quick, hot conditions, only a few will germinate, the rest remaining dormant in the soil.
Damping off will occur only if flats are kept too wet in the greenhouse without proper ventilation.
Transplanting
When the second leaves are developed and before the plants are too crowded, transplant them in flats, 3” inches apart, in a mixture of two-thirds sandy loam and one-third leaf mold.
Keep shaded for two or three weeks; then gradually give more light and, when larger, harden off in full sunlight before planting out in a permanent position about 2’ or 3’ feet apart.
An open, sunny location is necessary for the best development. In the shade, they will grow too spindly, with only small flower spikes. If too close to walls, they will mildew more than in the open.
The ground should be well-prepared for planting. A liberal application of well-rotted cow or sheep manure, with a sprinkling of bone meal mixed with the soil, which should be dug a foot deep, will produce fine growth.
Heavy, wet soils will require a slight addition of lime. Good drainage and a uniform supply of moisture during growth are essential.
Feeding
When the first crop of blooms has faded, cut the flower spikes off just above the foliage and keep them slightly dry for two or three weeks to give the plants time to rest before the new shoots appear above the ground.
When this takes place, cut the rest of the old stock off, sprinkle a teaspoonful of ammonium phosphate around each plant, rake it into the soil slightly, and water thoroughly.
From the new shoots appearing from the ground, select two or three of the strongest, and cut the rest.
The remaining ones will develop into fine spikes again. Do not force a new growth late in Autumn; rather, keep the plants on the dry side because if forced into bringing a third crop late in the season, the plants will soon exhaust themselves and gradually die.
Diseases
Mildew will attack plants grown close to a wall or planted thickly together, especially later in the Fall. Sulfur, dusted on the foliage, will act as a preventative before the disease is established.
Green Flower: This virus disease has been reported only west of the Rocky Mountains and is most prevalent near ocean areas.
A species of leaf hopper transmit it from infected weeds to the delphinium plants. All plants showing signs of the disease should be immediately discarded.
Crown Rot may be caused by several fungi prevalent in the eastern and southern sections of the United States, where high temperatures and humidity prevail during the growing season.
For the best information, send parts of infected plants to your state university for identification.
A Good New Variety Of A German Delphinium
Among the showy flowering herbaceous perennials, delphinium hybrids rank foremost because of their impressive flower spikes and the beautiful blue coloring of the flowers.
For about 30 years, the well-known German plant breeder, Mr. Karl Foerster, at Bornim near Potsdam, has occupied himself with raising new, hardy, and healthy rich-flowering varieties of the plant we call Delphinium cultorum.
His principles are:
- An ideal delphinium must be a strong growing plant, the tall spikes supporting themselves without staking. A halter (cord) ought to be sufficient for very tall plants for heavy storms and downpours.
- They must not be susceptible to mildew and other disorders.
- The stalks of the lowermost flowers must not break if soaked with rain.
- The lower flowers of the spike, even a long one, must not fade precociously.
- The spike must be tall and straight, like a cylinder, or have a pyramidal appearance.
- The varieties must be hardy even in the colder parts of Central Europe and must endure rather extreme dryness.
Glasturm
The variety shown in the picture is called Glasturm (Glass Tower). Its color is silvery blue with a dark center. The flowers have a fine vanilla scent and last very long.
Young plants are, of course, disappointing, but if they become older, they improve from year to year. The spikes are not very long, but when fully in bloom the variety is splendid.
44659 by Frank Reinelt