There are a number of annuals known as half-hardy, which have been sown in a greenhouse, frame or under access frames and must be allowed to grow there until such time as the weather is warm enough either to plant them out of doors, or in the case of cloches or frames to allow them to be removed. It is possible to make open-air sowings, with half-hardy annuals late, say, about the middle of May, but as a result the flowers are late also.

Greenhouse Sowing

Most sowings are made in February or March in the greenhouse at a temperature of 13 to 16 °C (55 to 60 °F). A sedge-peat and sand no-soil compost is brought and filled into boxes, pots or pans which have been thoroughly cleaned beforehand. They should be well crocked and provided with good drainage holes. The no-soil compost in the boxes is then firmed and made level and the seeds sown over the top thinly. The smaller seeds should be covered by sifting a little fine silver sand over the top.

Water the boxes or pots through the fine rose of a can and stand them on the staging of the greenhouse, shaded for the first few days with a sheet of paper.

Thin the seedlings out when large enough to handle and if necessary prick some of the seedlings out into further boxes. Give the plants a hardening off process (a) by gradually supplying more ventilation in the house, and (b) by taking the plants out afterwards into a frame before they are planted out into the open.

Be very careful of the damping-off disease when the seedlings are in their young stage. This can be prevented by (1) sowing thinly, (2) thinning early, (3) preventing the atmosphere of the house from becoming damp and stuffy, (4) by not watering overhead but by immersing the box or pot in a bath of water for a minute or two and (5) by watering with a ‘cure’ known as Cheshunt Compound.

Frame Sowing

Those who have no greenhouse may sow the seed thinly in frames, either in the soil direct or into boxes or pans stood in frames. It is convenient to sterilize the soil used and thus there is no weed competition nor trouble from diseases or pests.

Cloche or Access Frame Sowings

In this case the cloches are put into position over the ground a fortnight before seed sowing is to be done in order to warm the strip of land concerned. The seed is then sown in very shallow drills and the plants thinned out as soon as the seedlings are fit to handle. It is useful to prepare the soil be-fore sowing and make it as near as possible to the compost used for the boxes by adding sedge peat and sand. The ends of the cloche rows are closed with sheets of glass to keep out draughts. The plants harden off automatically under cloches and when the middle of May comes and there is no further fear of frost (at any rate in the south) the cloches may be removed.

Cut Flower Half-hardys

There are a few half-hardy annuals that are especially useful as cut flowers. China Asters, for instance, which normally flower in July and August; ten-week stocks which flower at the same time, East Lothian stocks, which from August sowings will flower from May to the end of August and from February sowings begin to flower in June; zinnias which can be cut in August and September, and cosmos which comes into use during these two months also.

The China Aster is usually sown at the end of March as are the ten-week stocks. The East Lothian stock seed is sown in July or August; the zinnias should be sown at the end of March and the cosmos about the middle of March.

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