How Plants Grow in the Greenhouse
The exotic plant trapped in its heated greenhouse is, by definition, in a very artificial situation. Not only that, it is also totally at the tender, or otherwise, mercy of the man in charge and the amount of heat that can be produced by the boiler in order to maintain an agreeable temperature. Some would have us believe that all the plants would be better off if they were returned to their little niche in the Caribbean,.or wherever. But this need not be so, and the perfect example of plants looking very much the better for enjoying the controlled conditions prevailing in the modern greenhouse is the poinsettia, Euphorbia pulcherrima, which is equally attractive as a compact pot plant as it is as an untidy shrub in its native habitat.
To grow at all in the greenhouse, plants need light, air, moisture, adequate warmth and some form of nourishment to stimulate growth. And all these need to be given at the correct level as too much or too little of any will at least be harmful, if not fatal, to the plant. Some plants, such as sansevieria, will tolerate extremes of conditions much more successfully than others, but even the sansevieria will turn up its toes and die if the growing mix is permanently saturated or if the temperature drops and remains below 45°F (7°C) for any length of time. It will almost certainly die should the conditions remain cold and wet for even a comparatively short space of time.
Over the years, generations of greenhouse gardeners in the commercial and the amateur field have grown plants of almost every description and learned to know the likes and dislikes of most of them. But you will meet few gardeners in the glasshouse business who are prepared to have themselves described as ‘experts’ — they probably, rather most certainly, know that plants in pots inare fickle things: you may well have an excellent crop one year, do exactly the same thing with the crop the following year, only to find that the results are disastrous. You can never become complacent about growing plants in greenhouses, there is always a new challenge and new problem to be met and one supposes that this is one good reason for taking a deal of pride in the job when it is well done.
For the beginner it is unwise to be too ambitious with the first greenhouse — in the first year or two it is much more sensible to experiment and get the feel of growing easy or simple plants before attempting more difficult subjects. Generally speaking, the more difficult the plant, codiaeums for example, then the higher the temperature it will require in order to succeed. This may mean making a start with an unheated, or cold house in which one can grow a reasonably interesting range of plants,planted in late April, for an early crop, hardy winter lettuce, even grapes above your head.
Camellias, one of the most beautiful of garden, do particularly well in the if it is well ventilated. Later in the year when summer warmth is about it will be possible to grow all manner of colourful and interesting plants in pots and hanging baskets — , tuberous begonias, calceolarias, streptocarpus, schizanthus; all sorts of beautiful things, really. The difficulty is, though, that none of these could be successfully overwintered in the cold greenhouse and fresh young plants would have to be purchased annually. This may seem to defeat the purpose of having a greenhouse which suggests that you should do everything for yourself, sow the seed, mix the growing medium and so on. But if you have no heat in the house then you have no alternative, and to stock a small greenhouse with young plants in late spring is not a costly business. The professional raises the plants for you in his heated greenhouses and you pay him for that service by purchasing his plants. And there are always plenty of fine quality young plants about for you to pick from — you can choose from a host of lovely things, put them into slightly larger pots when you get them home and have a very fine display that is well ahead of similar plants that you- may have raised from seed sown much later than those in the heated greenhouse.