The Cultivation of Half-Hardy Annuals
WHILE the cultivation ofcalls for slightly more attention than hardy annuals, there are no very great difficulties, and the extra facilities required can be confined to modest proportions. As their name suggests, will not tolerate frost, especially during the seedling stage, but they can be sown in the open in May, when the danger of frost is over, but this sometimes reduces their growing period so that they do not have sufficient time to reach maturity before the summer is over.
The only practical alternative is to sow half-hardy annuals in spring in a well-protected frame or, better still, in a cool, and so continue to give the young seedlings protection until the weather is mild enough to plant them out. Even certain hardy annuals will give better results if raised under glass, as they can be sown earlier and the young plants are not subject to the vagaries of spring weather.
Care should be taken not to over-coddle young seedlings and to ensure they are not starved. It is not only practice and personal experience which can fully give this skill, but common sense and a close observation of the behaviour of seedlings.
Seeds should be sown in clean pots, pans or wooden they can be pricked out into other boxes and gradually hardened off. During the first few days after pricking out, it is best to keep the boxes of seedlings shaded and with very littlein order to give the young rootlets a chance to take hold of the soil. Gradually increase ventilation until the lights can be removed altogether from the frames and hardening off is completed, prior to planting out in the prepared positions. From then onwards the method of cultivation is the same as that for hardy annuals. While they are being hardened off some half-hardy annuals will benefit from being topped in order to produce bushy, robust plants. and in particular respond well to this treatment, and the tops can be used as if additional plants are required.
The soil is about 1 inch below the edge of the receptacle. A thin layer of very fine soil- should then be distributed over the surface by means of a sieve. A dusting of fine silver sand may be given before sowing, then the seeds, can be more easily seen on this and distributed more evenly. The even distribution of seeds is a matter of great importance, as at the time of germination overcrowding can be fatal to the health and future well-being of the plants.
The seeds should be gently pressed into the surface with a flat, wooden presser, and then covered with very fine soil. The depth to which the seeds should be covered varies according to their size, and a good old-fashioned rule is to cover them to a depth equal to twice the thickness of an individual seed. When sowing has been completed, give the pans or boxes another gentle press so that the soil surface remains even, and water with a very fine rose. They can then be placed on the greenhouse staging or in a closed frame, and covered with newspaper. Maintain a temperature of from 50° to 55°, especially during cold, wet weather. After germination, a lower temperature is preferable. The time required for germination varies greatly.frequently germinate in 2 or 3 days, while Antirrhinums may take 2 or 3 weeks. It is as v/ell to keep the seed-boxes or pots covered with paper until germination takes place, as this will conserve moisture and save watering. It is essential, however, to remove the paper immediately the seeds germinate.
Once seedlings are big enough to handle, they can be pricked out into other boxes and gradually hardened off. During the first few days after pricking out, it is best to keep the boxes of seedlings shaded and with very little ventilation in order to give the young rootlets a chance to take hold of the soil. Gradually increase ventilation until the lights can be removed altogether from the frames and hardening off is completed, prior to planting out in the prepared positions. From then onwards the method of cultivation is the same as that for hardy annuals. While they are being hardened off some half-hardy annuals will benefit from being topped in order to produce bushy, robust plants. Salvias and Antirrhinums in particular respond well to this treatment, and the tops can be used as cuttings if additional plants are required.
If comparatively small numbers of plants are being grown, and if labour is available, better results will be obtained if certain half-hardy annuals are potted into small pots after being pricked out into boxes. These can be gradually potted on, and eventually put into the positions where they are to flower as quite. Annual Carnations, bedding Calceolarias, and Celosias will all give better results if treated in this way.
Avoid Starvation in the Early Stages
Before leaving the subject, a word of warning must be given about nourishment. During the early stages, half-hardy annuals are particularly susceptible to starvation if they are too crowded. Another dangerous time is while they are being hardened off. If unsuitable planting weather prevents the seedlings from being planted and they are left unattended for any length of time at this stage, the most serious damage will be done. In fact, all annuals must make steady and continuous growth, and they will rarely recover from a check caused by malnutrition. The easiest ways of avoiding this trouble are: do not sow too early, avoid sowing and pricking out too densely, and plant out young seedlings immediately they are ready. If, for any reason, there has to be a delay in planting out, then artificial feeding is the only remedy, and this can be given by means of liquid manure or by watering the boxes with a soluble.