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.
|Figure 1.2 The requirements of the plant for healthy growth and
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
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.