The plant

There is a feature common to all the above aspects of horticulture; the grower or gardener benefi ts from knowing about the factors that may increase or decrease the plant’s growth and development. The main aim of this book is to provide an understanding of how these factors contribute to the ideal performance of the plant in particular circumstances. In most cases this will mean optimum growth, e.g. lettuce, where a fast turnover of the crop with once over harvesting that grades out well is required. However, the aim may equally be restricted growth, as in the production of dwarf chrysanthemum pot plants. The main factors to be considered are summarized in Figure 1.2, which shows where in this book each aspect is discussed.

In all growing it is essential to have a clear idea of what is required so that all factors can be addressed to achieve the aim. This is what makes market research so essential in commercial horticulture; once it is known what is required in the market place then the choice of crop, cultivar, fertilizer regime, etc., can be made to produce it accurately.

It must be stressed that the incorrect functioning of any one factor may result in undesirable plant performance. It should also be understood that factors such as the soil conditions, which affect the underground parts of the plant, are just as important as those such as light, which affect the aerial parts. Increasingly, plants are grown in alternatives to soil such as peat, bark, composted waste and inert materials.

To manage plants effectively it is important to have a clear idea of what a healthy plant is like at all stages of its life. The appearance of abnormalities can then be identifi ed at the earliest opportunity and appropriate action taken. This is straightforward for most plants, but it is essential to be aware of those which have peculiarities such as those whose healthy leaves are not normally green (variegated, purple, etc.), dwarf forms, or those with contorted stems e.g. Salix babylonica var. pekinensis 'tortuosa’. The unhealthiness of plants is usually caused by pests or disease. It should be noted that physiological disorders account for many of the symptoms of unhealthy growth which includes nutrient defi ciencies or imbalance. Toxics in the growing medium (such as uncomposted bark) or excess of a nutrient can present problems. Damage may also be attributable to environmental conditions such as frost, high and low temperatures, high wind (especially if laden with salt), a lack or excess of light or water.

Weather plays an important part in horticulture generally. It is not surprising that those involved in growing plants have such a keen interest in weather forecasting because of the direct effect of temperature, water and light on the growth of plants. Many growers will also wish to know whether the conditions are suitable for working in. Climate also pays particular attention to the microclimate (the environment the plant actually experiences).

A single plant growing in isolation with no competition is as unusual in horticulture as it is in nature. However, specimen plants such as leeks, marrows and potatoes, lovingly reared by enthusiasts looking for prizes in local shows, grow to enormous sizes when freed from competition. In landscaping, specimen plants are placed away from the infl uence of others, so that they not only stand out and act as a focal point, but also can attain perfection of form. A pot plant such as a fuchsia is isolated in its container, but the infl uence of other plants, and the consequent effect on its growth, depend on spacing. Generally, plants are to be found in groups, or communities.