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The
Right Dose
21 May 2003
Garden centre shelves are stacked high with
an amazing array of fertilizers. Many, it is
claimed, are ideal for every crop and plant
in your garden. It is not as simple as it would
appear though. Apply the wrong nutrients and
the tree may refuse to fruit and your cabbages
will remain stunted.
 Fertilizers
are sold in three forms, powder, granular or
liquid. The latter is immediately available
to the plant whereas the other two have to be
dissolved by available water in the soil before
they can be absorbed by the plant roots.
Slow release fertilizers are granular and provide
the nutrients over a 3-6 month period. Liquid
foliar feeds are applied to, and absorbed through,
the leaves.
There are three main nutrients in most fertilizers.
N (nitrogen ), P2O5 (phosphate) and K (potash)
each shown as a percentage. Specialist fertilizers
such as those sold for roses contain minute
quantities of trace elements such as manganese,
zinc and iron. Without these the rose foliage
would be discoloured and the plant stunted.
Each of the main nutrients has a roll to play
and certain plants need more or less of each.
Nitrogen promotes growth and when applied to
the lawn makes the grass grow more quickly with
a rich, dark green colour. It is ideal for leafy
vegetables such as cabbage.
Extra nitrogen in the feed will speed up the
growth of a hedge producing soft stems, which,
unfortunately, are more prone to frost damage.
 Phosphate
is essential for good flower colour and encourages
sturdy growth. Potash is needed to produce a
good root system, helps the plants to resist
disease and firms up soft growth.
A high nitrogen fertilizer can be used during
late spring and summer to promote extra stems
and foliage. When followed by high potash feeds
in autumn, that growth will be hardened and
immune to winter frosts.
The most popular liquid tomato feeds have a
potash reading double that of nitrogen. Lawn
feeds are usually high in nitrogen. Many others
are balanced with an equal percentage of the
three main nutrients
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