The cool greenhouse is one which is kept absolutely frost free and in which a minimum temperature of 4 C. (40 F.) is maintained. If the temperature is nearer to 10 C. (50 F.) so much the betler for many plants, excluding annuals which much prefer a temperature nearer 4 C. This kind of greenhouse is sheer delight for the adventurous gardener, for compared with the unhealed greenhouse the scope is wide indeed. There is no difficulty in having plants in flower during every month of the year. If you wish to make more practical use of such a house it is possible also to grow tomatoes during the summer months and letluces during (he winter.
It is desirable to have a small propagating frame in a cool greenhouse in which a h iijh temperature can be maintained in the spring say 16 to l1SnC. (60 to 65 F.). This is used for germinating seeds of begonias, gloxinias, antirrhinums, lobelias and a host of other plants which are going to be grown on throughout the summer.
1 have said that w ith this kind of greenhouse it is possible to have colour throughout the year, so let us now consider some of (he plants which can be grown lo provides succession ofcolourand interest. If we divide I lie year into quarters, then in January. February and March wc can have Azalea indka. cinerarias. Primula obconka and the most popular of all flowering bulbs such as daffodils, narcissi, tulips and hyacinths in bloom. The joy these flowers can hring in these bleak, often grey months will be readily appreciated.
In the second quarter, April. May and June, the pleasures are different for plants
like the pelargoniums (geraniums) fuchsias. the large-flowered calceolarias and thai most lovely of half-hardy annuals, schizanthus, (the Poor Man's Orchid or Butterfly Flower) arc coming into flower. Also coming into bloom now are such autumn-sown annuals as clarkias. godet-ias, stocks and salpiglossis.
In July. August and September even the cool greenhouse can begin to look exotic with begonias, gloxinias and fuchsias continuing lo bloom, and achimenes. Lilimi cniruiwn and L. speciosuni rubrum. pelargoniums and Campanula isophylla all making their contribution.
In the last three months of the year there are chrysanthemums, pre-cooled narcissi, daffodils and hyacinths, abuii-lons, 2onal pelargoniums, Lorraine begonias, primulas and cinerarias in flower, and Solanum capsicastrum. the popular Winter Cherry, wilt be bearing its orangered berries.
The perpetual-flowering carnations, or tree carnations as they ate sometimes called, are ideal for growing m a greenhouse with a minimum temperature of TC. (45 F.) and these will provide a continual display of flowers throughoul the year.
The cool greenhouse needs even more ventilation lhan the unhealed greenhouse because of' the type of plants grown in il. Most of these need a free circulation of air and can be harmed by too high a temperature. It is. therefore, necessary to use the top and bottom ventilators during ihe spring, summer and into early autumn, and (he top ventilators should also be used throughout the year whenever the weather is what gardeners call "open', (hat
is to say whenever the air is not cold or damp,
Anolhcr point lo keep in mind with this kind of greenhouse is thai it is inadvisable to sow seed too early. To use tomatoes as an example, 1 would not recommend sowing seed of this fruit until the middle of March and then only in a warm propagating frame and they should certainly not be planted out in a bed or in pots or boxes until towards the end of April. Tomatoes give a better return if they are planted out later when the days are longer and the sun warmer. Generally speaking, most propagating carried out in a cool greenhouse should be done three weeks to a month later than that in a warm greenhouse.
An important environmental factor in managing a cool greenhouse successfully is that the atmosphere in winter must be kept much drier than thai in warmer houses, and the plants must be watered with more care. During winter, watering should be done during ihe early part of the day raiher than in the afternoon or evening. If (he atmosphere in ihis type of greenhouse becomes loo moisture laden or stagnant due to faulty ventilation then ii is only loo easy for botrytis lo gain a hold on plants such as pelargoniums and fuchsias and be the cause of many losses.
If these cautionary words are heeded and your cool greenhouse is fully exploited you can be sure that ii will give you enjoyment in full measure. If you turn to the Quick Guide to Decorative Plants on pp, 1.14 to 136 or refer to ihe notes on individual plants you will see how wide is the scope of ihe cool-greenhouse gardener.
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