Agriculture Reference
In-Depth Information
What about ventilation?
Most polytunnels rely on nothing more complicated for ventilation than opening
the doors at either end, although more sophisticated options, such as ridge vents
and ventilation skirts, are available. Ventilation is vital because it is your only
method of controlling heat in the polytunnel, and also the only method of reducing
humidity. If the tunnel stays humid for long, the plants are at increased risk of
attack from moulds and other fungi.
Except in freezing weather, you should open at least one end of the tunnel as
soon as possible after dawn, and close it again at least an hour before sunset. In
sunny conditions, it is important to leave the doors at both ends open to allow a
through draught.
What about water?
As polytunnels are unaffected by rainfall, having an adequate watering schedule
is crucial to healthy plant growth. Especially in the first year, it's important to
monitor the condition of the beds constantly so that you get a really good idea of
plant requirements. Until you get the hang of it, a moisture meter is invaluable.
Naturally, how much water you need to give, and how often, depends on what
sort of soil your beds contain. Light, sandy soils hold water poorly and should be
watered twice a day during warm weather. Fail to do this and you are very likely
to damage or even lose the harvest. Perversely, heavy clay soils can actually be
more difficult to manage. In cool, cloudy weather they need watering only once
every few days, but just a day or two of sunshine dries out the surface layer; there
is still plenty of water deeper in the earth, but many food plants have shallow root
systems and depend on moist conditions close to the surface. Lettuce, for exam-
ple, suffers sooner than most and its leaves don't have to wilt very far before they
completely lose the ability to come back. Stressed plants bolt, which is a natural
survival tactic so that the species continues even if the individual plant dies, and
for many crops bolting means the end of the harvest.
However often you need to water, it can take a big chunk out of your day. If the
idea of spending a great deal of time hand watering everything doesn't really
appeal to you, take heart - there are several different options available.
Automatic systems start with a battery-operated timer connected to the mains
water supply, or to a reservoir with some header space to provide pressure. The
water is then directed through a branching hose system to where it's needed.
Even if you normally activate the system by hand, if you are going away in the
middle of the summer, make sure you are familiar with using the timer before
you go. Then you will be able to leave with confidence, knowing everything is
going to be fine back home while you're lying on a beach somewhere.
