Planting Density
The number of plants to grow per square metre, or
the planting density, is a trade-off between increased
yield and decreased quality. While close
spacing produces increased yields per square metre
it results in smaller flowers and lower quality. Stems
are generally weaker and longer due to the decreased
light levels. The incidence of disease can
be higher due to the decrease in air movement
caused by the crowding. Increased space between
plants results in better quality, but lower yields per
square metre.
Planting density varies with plant size, the number
of years between replanting, the sensitivity of the
crop to disease, the method of harvest and the
staking requirements. It also varies with each plant
species; most seed catalogues or supplier’s guides
give recommended spacings. Some spacing
principles are common to most crops. For example,
the larger the size of the mature plant the more
room that will be needed between plants. Gypsophila
will need much more room than a smaller
plant like zinnia. In general, perennials are planted
less dense than annuals to allow for the several
years of growth between digging up and splitting.
Plants that are prone to foliar diseases, for example
snapdragons, which are susceptible to powdery and
downy mildew, will benefit from a wider spacing
due to the increased air circulation. Perennials
which need staking may benefit from an increased
density where the flower stems tend to support
each other
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