A green plant has a root, a stem, leaves and ultimately in most cases a flower, followed by a fruit or seed, and it will, if given suitable growing conditions, adhere to a fairly regular pattern of growth. The native habitat of many of the plants we grow is often vastly different, climatically speaking, to that prevailing in Britain, and a greenhouse is merely a device for overcoming climatic disadvantages. Modern breeding, however, has very much altered the basic characteristics of many plants, simply because nature’s own handiwork may not suit the demanding horticulturist in respect of flowering or fruiting habits. The plant breeder has endeavoured to blend all the best qualities of many different varieties and groups of plants to ensure optimum quality and performance, not always entirely successfully, but generally with a fair measure of success, as can be seen when one looks at the wonderful modern range of all the different plants and crops we grow, not only in our greenhouse, but out of doors as well.
The really important thing to appreciate about greenhouse gardening is that while nothing is vastly altered in the whole cycle of growth from seed or cutting to mature plant, we are dealing, in many cases, with groups of plants whose natural habitat is far away, and this makes them just that bit different from the plants which are true natives. There is more to this philosophy than mere tenderness and lack of ability to stand up to frost. Tomatoes came from sunny South America originally and still, despite intense breeding, yearn for all the light they can get, especially in their early days when we try to induce them to grow in our dreary winter. Many plants are natives of the Equatorial forests and long for the hot humid shady conditions typical of these regions. There are also lots of perfectly hardy plants which are not always grown out of doors because we wish to extend or alter their season of production, lettuce being a good example of this.
The really vital thing to appreciate with all greenhouse gardening is that a largely artificial growing regime is being created merely for our own convenience. There is light and air, but little or no moisture unless we supply it. The sun often shines to excess in summer and steps have to be taken in expel the trapped heat. Plants grow much more quickly in a greenhouse than they do out of doors, so that more moisture and nutrients are needed to sustain this rapid growth.
DAY AND NIGHT TEMPERATURE DIFFERENCE
Another highly important issue with all plants in a green-house is the differing conditions between day and night, especially during spring or autumn when sunny days are often followed by cold nights. The result is a tremendous temperature variation which can give rise to unbalanced growth.
A gardener, to a certain extent, creates an exclusive grow-ing environment in his greenhouse which is different from that in other greenhouses, and certainly very different from that in the garden. This is especially the case where pot plant growing and ring culture of tomatoes and other plants are concerned, involving limited quantities of growing medium which can, at the outset, be pest and disease free and in a certain physical and nutrient state, more or less under the control of the gardener. This is a tremendous advantage as results are much more predictable than they are out of doors. This facet should be fully exploited and no chances taken with doubtful materials, particularly with reference to the various propagating mediums, seed sowing and potting com-posts used for various crops.