Tomatoes can be grown in the greenhouse using several different methods.
The majority of them attempt to get round the major problem of growing
tomatoes in a greenhouse year on year - pests and diseases in the soil.
It only takes a couple of years growing tomatoes in the greenhouse for
the soil to become "sick". The only solution is to remove and replace
the soil or sterilise it using heat. Both are expensive and
time-consuming. For this reason different cultural methods have evolved
which only use a small amount of disposable soil / compost or none at
HOW TO GROW GREENHOUSE TOMATOES - GROW BAGS
Possibly the commonest method of growing tomatoes in greenhouses is to
use grow bags. These are simply plastic bags filled with a compost
mixture. Cut two holes in the top and grow your tomatoes in the bags.
This method certainly gets rounds the soil contamination problems
because at the end of the season the grow bags are disposed of and new
ones bought for the next season
Costs are on the low side; new grow bags cost relatively little and the
cost of liquid fertilise is minimal. Given the amount of tomatoes
produced using this method, it is also financially sensible, and the
tomatoes produced are of course home grown and better tasting compared
to shop bought tomatoes. Other main advantages and disadvantages are
warms up quickly.
Requires very frequent watering. Holidays will
be a real problem.
small amounts of compost required.
Salts can build up in the compost.
Eliminates many pests and diseases from the compost.
Getting the amount of watering correct can be
difficult. Plants can easily be waterlogged.
Nutrients and water
levels can be well-controlled
One variant of growing tomatoes in grow bags is to puncture the lower
part of the plastic container. If the grow bag is on soil the longer tap
roots of tomatoes which search out water may well then grow into the
soil below and find a good supply of water. In some of the examples we have seen, this is
repeated year after year with little or no introduction of pest and
disease into the soil below. In essence, this method then becomes a
variant of ring culture (see below).
One word of warning though about the above. If the depth of the grow bag
is small, some of the fibrous roots may find their way into the soil
below and this has the distinct possibility of introducing pests and
disease into the soil. Keep this in mind if your grow bag tomatoes show
signs of disease.
HOW TO GROW GREENHOUSE TOMATOES - DIRECTLY IN THE SOIL
The key advantage of growing tomatoes directly in the soil is that you
simply plant them without much preparation. The key disadvantage is that
within a very short time pest and diseases will build up. The only
solutions are to either remove the top soil annually and replace it with
new sterile soil, or, to heat sterilise the soil each year.
The key good and bad points are summarised below:
grown this way taste better compared to other methods.
Pests and diseases will be a problem after the
first year. Soil should be replaced or sterilised annually. This
retains moisture well and therefore requires less watering.
Soil is slower to warm up compared to other
Other than growing tomatoes directly in the soil for the first year of a
greenhouse, we do not recommend this method. Pest and disease
accumulations in the soil will quickly become unmanageable.
BOTTOMLESS POTS (RING CULTURE)
This is not complicated and many greenhouse gardeners use this method,
or a variant of it, without realising. Large plastic pots have their
base cut out, and they are then placed directly on the soil, grit or
gravel. Click the picture on the left to see an an enlarged version.
When the tomato plants are ready to be transplanted and all
danger of frost is passed, the bottomless pots are filled with compost
and the tomato plants are transplanted into them.
The theory behind ring culture of tomato plants in greenhouses is based
on an understanding of their root system. Tomato plants have two types
of roots: the roots near the surface search out primarily food and
nutrients; the lower tap root searches out water. Click here for more
information on tomato plant roots.
The standard method of greenhouse using bottomless pots (ring culture), tomatoes or other
vegetables, is as follows:
Dig out the top 15cm / 6in of soil from the bed.
Replace the removed soil with 15cm / 6in of
grit, gravel or similar material.
Place the bottomless pots on the gravel
Water the bottomless pots with liquid tomato
feed twice a week
Water the grit (without liquid feed) at least
every other day, more often in warm conditions.
At the end of the season, wash the grit well in
running water and then store it dry for use next year.
The standard method above uses a 15cm / 6in layer of grit between the
bottomless pot and the ground below the grit. The taproots will grow
through the grit to reach the moisture in the soil below. Many gardeners
have been using the above ring culture but without the layer of grit.
The bottomless pot is simply placed directly on the soil. I know several
greenhouse gardeners who have been doing this for many years with great
results. It saves buying the grit, washing it each year and then storing
it for next year. The choice is yours.
The advantages and disadvantages to bottomless pots (ring culture) are summarised in the
Much cheaper than growing directly in the soil.
Frequent watering is required.
Over-watering is unlikely to be a problem.
Getting the correct level of nutrients can be tricky.
Compost warms up early in the year.
Pest and disease problems will be
to growing directly in the soil.
HOW TO GROW GREENHOUSE TOMATOES - OTHER METHODS
The above three methods cover the most common methods of growing
tomatoes but there are others. Hydroponics, grafted and disease
resistant plants, straw bale culture
are nut a few. However, the the main ones in the main article above are
probably the only ones worth considering for the amateur gardener.
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