This section is from the book "How To Make A Flower Garden", by Wilhelm Miller. Also available from Amazon: The Well-Tended Perennial Garden: Planting and Pruning Techniques.
From a coldframe may be had violets, wallflowers, forget-me-nots and pansies in March, "hepaticas" and trailing arbutus in April, together with wood-violets, wood-anemones, and the many other wild flowers, thus starting the flower season two months ahead. Again in October and November, when everything outside has been nipped by early frosts, the coldframe preserves a few choice heliotropes, begonias, Marguerite carnations, nasturtiums grown in pots, scarlet sages; and the queen of the autumn, the chrysanthemum, is seen in all her glory.
Violets for growing in coldframes are propagated, like strawberries, by runners. Great numbers of these are formed in April just as the flowering season closes. Take as many as you need to fill the frames the following year - say thirty-five to forty-five for a six- by three-foot sash, remove the old plants, and put the young ones in their places. Or, should the space be required for other things, place the young plants three inches apart in shallow boxes or in small pots until the beginning of May, when they should be planted in the open ground, kept watered and cultivated in summer, and transplanted into the frame, seven inches apart, by the middle of August. Flowers may be picked from early October until late November. In sections where the thermometer registers zero it will be necessary to keep the frames comfortably covered. In warm sections flowers may be picked all winter.
When plants are frozen, they should be left so, but during long warm spells air must be given or they will "damp off," or rot. The sunshine in February will bring the flowers out again, and they will continue to bloom until April. In summer all plants should be frequently sprayed to keep them free from the red spider and green fly, otherwise they will give trouble in winter.
The best single blue varieties are California and Princess of Wales; the latter has the larger flower and longer stem. Among double blues, Marie Louise and Farquhar dark are favourites, but Lady Hume Campbell or light Farquhar is the best. This variety has a more rugged constitution, and blooms later.
Forget-me-nots are raised to perfection in coldframes. Sow the seed in July in a sheltered spot in the open ground. In four weeks, or when plants are large enough to handle, transplant three inches apart; water and grow along till late in September, then plant seven inches apart in frames, and keep them growing till frosts set in. A covering of three inches of dry leaves or straw should then be put over them. The frost will not hurt them, but the sun shining on them when frozen burns the leaves. When the weather gets warm in spring, remove the leaf mulch. The plants bloom during April and May.
With the same general treatment, but leaving them in the open, the plants start to flower toward the end of May, and bloom continuously till July. The seed then falls, in due time germinates, and flowers appear next season. Old plants will bloom several years, but young plants each season give best results.
Wallflowers in coldframes are very satisfactory. Sow the seed in April or May in the open ground or in "flats." When the seedlings are large enough to handle, transplant three inches apart. They will crowd each other in four weeks, when they may again be transplanted, giving each plant a square foot. By the first of October they will be twelve inches high, and bushy, and may be planted singly into six- or seven-inch pots, or several in boxes, and removed to the frame, where they should be covered to prevent alternate freezing and thawing. They do not like high temperature, so the sash should be removed on all clear days, especially in February and March, as they start growing then. They flower in April. We have heard that around New Rochelle, N. Y., some plants have been known to flower after being left outside all winter, but we have never seen them.
Mignonette is always welcome and a general favourite in the garden and yard, but it is seldom seen in the window garden or coldframes, although it can be seen at its best when grown in either position during the fall and winter.
Sow the seed of the "Machet" or "Allen's Defiance" strains about August 15th, in small pots, putting four or five seeds in each. Water, and cover them with a sheet of newspaper. If the paper is kept moist the soil will not require watering again before the little plants come up. If more than two seedlings grow in each pot, they should be pulled out. For pot culture, as the pot is filled with roots more room should be given, until each has been potted into a six-inch pot. The stalks should be supported. After the center stalk flowers and is cut away, many side shoots will push out, and each will have a spike of flowers. Mignonettes may be kept in bloom all winter. When plants are to be grown in frames, they may be planted there as soon as the small pots first fill with roots. By planting several in a large pot a large specimen can be grown which attains a height of two feet and a diameter of the same.
Pansies are raised from seed sown each season. It is not necessary that they should be bought each year, as home-saved seed is equal to any from the store, always providing a good strain has been secured at the start, as Henderson's Mammoth Butterfly, Giant Trimardeau, or German mixed. They do best in frames, or "flats." They take kindly to transplanting, and can be moved when in full bloom. A good watering always brightens them up after moving. For early spring use in the window box, or for cut flowers in the coldframe, or for planting in beds, sow the seed the middle of August. When large enough to handle, about the time the third leaf shows, transplant singly three inches apart in shallow boxes. Attend to watering until they freeze, then cover with dry leaves and leave till spring starts them into growth again. They will stand a sharp frost. Ten degrees will not materially affect them, so they may be planted out in beds or window boxes the first week in April. For summer and fall flowering, sow seed in April, grow along, and plant in a shady bed eight inches apart.