Agriculture Reference
In-Depth Information
as you have the slug situation under control - if not, water in the morning
instead. In warm weather, make sure that the doors at both ends of the tunnel are
opened as early after dawn as possible so that air can circulate freely through the
tunnel. As usual, close them again an hour before sunset to retain as much
trapped heat as possible. This is especially important when you are growing
tomatoes, as they dislike fluctuations in temperature, which can cause problems
with the developing fruit.
Never underestimate how much water the tunnel will need during summer, and
check water levels frequently using a moisture meter or by digging a small test
hole with a trowel in the middle of a bed. Areas with big, thirsty plants will need
more water than those with small plants or a moisture-retaining mulch. On a hot,
dry day a fully grown tomato plant can use two litres of water for transpiration.
Naturally, this level of demand means that you have to pay close attention to the
water supply in your tunnel. Water rationing could spell disaster in no time at all
unless you have a contingency plan, although hosepipe bans usually still allow
a hose to be used to fill watering cans.
Water security
All polytunnel owners, whether on mains water or not, need to have a backup supply
in case their usual supply of water fails. At the very least you should have a few
large water butts very close to the tunnel, and keep them topped up with fresh
water at all times in summer. We recommend the use of a self-adhesive product
called 'tunnel gutter' (made by Northern Polytunnels but widely available through
retailers) to harvest rainwater falling on the tunnel and direct it into water butts
positioned at the corners. The butts are best placed at the north side of the tunnel
to avoid shading the interior, and can be linked together near the bottom using a
butt-linking kit.
Plants in pots, modules and other containers pose special problems in hot weather,
as once the compost starts to shrink away from the sides of the container it can be
difficult to re-wet it. A 20-minute soak in a watering tray will work, but a more elegant
and time-saving solution is to make a capillary bed on a bench or shelf. This is
made up of a sheet of capillary matting covered with microporous membrane, often
sold with it, linked by a wick to a reservoir of water. Provided the reservoir is kept
full of water (preferably rainwater, to prevent the wick from clogging up with
deposited lime), the matting will stay wet, and pots placed on top of it and watered
in will stay moist indefinitely.
To prevent minerals from concentrating on the soil surface over time, plants that
spend a long time on the capillary bed should be taken off once a week, allowed to
dry out a little, and surface-watered before replacing them on the matting. Capillary
beds do not work for pots taller than 15cm: you need micro-irrigation for this, which is
available from good gardening suppliers as well as some specialist companies (see
Chapter 2, page 23).
