Agriculture Reference
In-Depth Information
the humidity level right. The need to maintain air
circulation is essential as the opportunity arises.
Excessive feeding with high nitrogen fertilizers
should also be avoided because it can create soft
growth which makes them vulnerable to disease and
excessively soft and vigorous plants can be checked
(their growth interrupted) when planting out.
Growing seeds in open ground
The success of sowing outdoors depends greatly on
preparing the seedbed; the
tilth
needs to be matched
to the type of seed, soil texture and the expected
weather conditions (see soil structure p. 147).
Figure 11.5
Bedding plants in nursery
Tilth
is the crumb structure of the seedbed.
Weeds need to be dealt with by creating a stale (or
false) seedbed, hoeing or using weedkillers (see
p. 194). Nutrients, especially phosphate fertilizer, are
worked in and the ground levelled to receive the seed.
The process of sowing seeds in the open can be by
broadcasting or sowing in drills (hand or machine) and
is shown on the companion website.
The
sowing rate
will depend on the species and the
likely losses that can be estimated from:
X
seed viability
(see p. 128)
X
germination percentage
- a measure of potential
emergence under ideal conditions; the proportion
of seeds that produce healthy seedlings under
laboratory conditions
X
fi eld factors
- seed emergence under fi eld
conditions, i.e. allows for quality of the seedbed
and weather conditions.
Sowing dates in the open vary according to the plants
concerned (see germination temperatures, p. 68) and
the location where they are to be grown. The general
rule is not to sow before the soil warms up to the
appropriate temperature.
Figure 11.6
A frameyard: a collection of cold frames
each covered with 'lights' which are sheets of glass
(or clear plastic) in a frame
ground without a check in growth caused by the colder
conditions, wind chill and a more variable water supply.
As the pricked-off seedlings become established, they
are moved to a cooler situation, typically a cold frame
(Figure 11.6), which starts off the process of hardening
off by providing a closed environment without heat.
After a few weeks the cold frame is opened up a
little by day and closed at night. If tender plants are
threatened by cold or frosts, they can be given extra
protection in the form of easily handled insulation such
as bubble wrap or coir matting put over the frame.
Watering has to be continued and usually the plants will
use up the fertilizer in the compost so need applications
of liquid fertilizer. The hardening process then continues
with the frame lid ('light') gradually being opened up
more to allow air circulation day and night. Ideally
the plants have been fully exposed to the outdoor
conditions by the time it is ready to plant them out.
The young plants are very susceptible to fungal
diseases while in the cold frame because of the high
density of planting and the difficulties with keeping
Aftercare
There are advantages in providing protection for the
developing plants including windbreaks or fleece (see
Figure 11.7). Where residual herbicides are not used
there needs to be ongoing control of emerging weeds
while they are in competition with the seedlings and
young plants (see p. 208). If the seedbed was well
watered then there should be no further need to add
more water; indeed there are advantages in not doing
this in terms of water conservation (see p. 156) to
encourage deeper rooting and the prevention of soil
capping (see p. 150).
