What Plants Need to Live
How Plants Live
It would be wrong to make a special issue of the physiological aspects surrounding plants being grown in a greenhouse, as the mechanics of growth and all the associated facets are common to all green-leaved growing plants. The only special case which could be made foris that they will, in most cases, be growing a lot quicker than they would out of doors, so that everything will generally happen faster. On the other hand it is possible to control the environment of a greenhouse to fairly fine limits, which is a distinct advantage, compared to the resigned acceptance of conditions as they occur out of doors. Perhaps then, taking all things into account, there does exist the need for a nore complete understanding of basic physiological processes if greenhouse gardening is to be entirely successful.
All green plants, given air and moisture in the absence of any inhibiting or restricting factor, will grow at a rate commensurate with the light level and temperatures to which that particular species or cultivar of plant is attuned. This rather complicated sentence perhaps requires some explanation. A tomato plant, a native of South America originally, has an inherent need for high light intensity and warmth. For it to grow, flower and produce fruit successfully, it is therefore incumbent on the gardener to provide for these conditions as far as possible.
Plant a tomato plant outside in Britain during the month of March, instead of in the greenhouse, and if it does not die fairly quickly it will certainly not grow to any great size, but will tend to debilitate. Conversely, plant a cabbage, a native of Europe, outside in March and, provided it has been suitably acclimatized, it will grow quite happily and in time produce a heart. Put the cabbage into the warm greenhouse environment suitable for the tomato and it will certainly grow at great speed, but it is unlikely that a heart will be produced, the plant developing vegetatively and showing elongated growth.
These rather elementary examples by no means explain why the tomato and the cabbage must have an environmental regime compatible with their metabolism. One point, however, which does clearly emerge is that the velocity of growth of plants is invariably increased when they are put into an environment warmer than that to which they are attuned by inheritance. It is highly important to remember this elementary issue and to think of it categorically: the completely hardy plant which will survive out of doors all year in Europe in category 1; half-hardy plants such as the pelargonium in category 2; the tender tomato in category 3; and the very tender melon in category 4.
For more information, see Plant Processes – How Plants Grow