Greenhouse Gardening FAQs
How do you sow seeds ?
The method of seed sowing in a greenhouse remains constant whether the plants being raised are vegetables for inside or out, bedding flowers to be planted out for the summer, or to be grown in pots for temporary life in the house.
The receptacles needed are shallow pots or trays and the compost, or soil mixture, used must be light in texture. (Compost in this context must not be confused with the compost made by rotting down vegetable refuse for digging into the soil during the winter.) For everyday use a compost based on peat, proves in every way satisfactory. It is light and clean to handle, is sterile and therefore free from organisms that attack small seedlings, and its texture encourages the seedlings quickly to make a greatly ramified system of roots.
The shallow plastic pots or trays are filled with the compost, which is only lightly pressed down. Then water thoroughly with a fine rose, making sure that the compost is thoroughly wetted, and allow it to drain. Sow the seeds very thinly and cover with no more than a light sifting of compost.
Unless the pots or trays are stood in a plastic covered propagator it is best to slip each into a transparent plastic bag. This will provide the right degree of humidity that seeds need in order to germinate, provided the end of the bag is slipped underneath the container so that it is sealed. Whenhas obviously taken place — apparent from the tiny green spots on the surface of the compost — air can be admitted, and the seedlings will then grow quickly. In a few days the bag can be removed altogether.
However, at this stage the small seedlings must still be kept lightly shaded from the hot sun or they may get burned up. This is one of those factors that calls for the judgement developed with experience.
Once the seedlings are big enough to be taken hold of by their first pair of leaves — never the stem, for fear of damaging it — they are transferred to a position where each can begin to realise its potential. For the best results, this means giving each a small pot of its own, or spacing them out 2in. apart in another tray, still using the same peat-based compost.
If they are summer bedding plants the seedlings can stay in these containers until they are ready to be put out, but if they are pot plants for the home they will need “”, being given progressively larger pots as the roots reach out and begin to encircle themselves in their smaller ones.
What kinds of bedding plants?
Ageratum for soft blue edgings, antirrhinums that give tall spikes of snapdragon flowers, asters with huge shaggy blooms, begonias that bloom for four months at a stretch; cosmos for cutting, dahlias too; sweet smelling pinks and tobacco flowers; salvias that can be purple as well as scarlet, alyssum, lobelia and French marigolds for bold ribbons alongside rose beds; and annual phlox, petunias and verbena that trail and smother the ground. But there are so many more if you only study the seed catalogues. Once you have a greenhouse even these take on a new dimension.
And what kinds of pot plants?
Big-flowered begonias, brilliant calceolarias with highly coloured flowers like pouches, starry cinerarias in every colour there is; cyclamen for winter, gloxinias for autumn, freesias for spring and primulas for summer. Schizanthus that they call the poor man’s orchid, African violets, saintpaulias that flower the whole year round. But again there are so many more, just to be found for the looking through the catalogues.
When to sow?
The lengthening days of March, as early as possible, are the most favourable time for bedding plants, but sowing seeds of pot plants can go on all through the spring and early summer. Helpfully, seed firms always put on the packets the best time for sowing.
Some pot plants can be raised from bulbs and tubers also, both of them nature’s storehouses of plant food and rudimentary growth. The big begonias, trumpet-flowered gloxinias and funnel-like gesnerias are plants that can be grown in this easy way. You simply have to put each tuber or bulb in a small pot of compost in March or April, keep it lightly watered and on the greenhouse bench, when it will turn into a lovely flowering plant that can be brought into the home when it has almost come into flower, which is generally about four months later.
Isn’t watering tricky ?
Watering. That’s a key word in managing greenhouse plants and seedlings. The vital point is to give a little less than you would think the plants could do with. In hot weather they may be greedy for it, but most of the time in our climate plants are happier just on the dry side.
Automatic equipment can be bought that will look after the whole business of watering, but a much less expensive way is to buy the special self-watering capillary matting for lining greenhouse benches. If this is kept damp it allows the plants, by this natural process, to take up just as much water as they need.
All greenhouse plants, whether they are fully grown, or just seedlings, need feeding. Specially blended liquid fertilisers, like Liquid Garden ‘Plus’ and Liquid Tomato ‘Plus’, will provide all the essential nutrients in exactly the right proportions. For house plants there is a particularly convenient liquid feed called ‘Kerigrow’, which is dispensed drop-by-drop straight from the bottle and watered in.
How do you know when to feed?
After a plant has been growing in compost for about six weeks it will need the supplement, and then it pays to give a little food each week.