One of the joys of growing tomatoes in pots is that they do so well, and if the pots can be moved as the sun moves then one can pick tomatoes well into winter, which is a real bonus.
Growing tomatoes in containers is a viable option for gardeners who have limited space, plus it also allows one to be creative – to experiment with different varieties and to turn a few container-grown tomatoes into special features. One of the nicest things is that the pots can be moved to take advantage of the changing position of the sun as summer moves into autumn and then winter. Provided their new positions are also warm and sheltered, the plants can continue to produce tomatoes into the winter months.
Tomato types for containers
Both determinate and indeterminate tomatoes can be grown in pots. This includes cherry tomatoes, which are usually indeterminate.
Determinate tomatoes are bush tomatoes that grow to a set height of about 1,2 metres. While it is not absolutely necessary to stake them, you may find that as the fruit develops it begins to weigh down the branches and they need supporting. Staking can also help to expose the fruit to the sun for ripening. Good determinate producers for pots are Red Khaki, Heinz 1370, Rodade and Marianna (a Saladette tomato).
Indeterminate tomatoes are ramblers that just keep on growing unless you stop them. Such tomatoes need special treatment if grown in a pot. A sturdy trellis or framework is necessary and the plant should be trained up and tied onto the support. This gives you more control over the fruit production and the shape of the plant. Good producers are cherry tomatoes such as ‘Bite Size’, ‘Red Cherry Sweetie’ and ‘Yellow Pear’. The full sized tomato ‘Moneymaker’ (which is open pollinated) and the hybrid ‘Sundance’ (which is very disease resistant) are also good options.
The bigger and deeper the container, the better it is for growing tomatoes, although if it is too big then you lose portability. Make sure the pots are at least 40 cm in diameter and depth. A large container prevents the roots from getting too hot and the potting medium from drying out too quickly. Make sure there are enough drainage holes.
The drawback of containers is that the nutrients leach out because of the water flowing through the container and out. This means starting off with a rich growing medium and following this up with regular feeding.
One option is to make a 50:50 mix of potting soil and (reconstituted) palm peat. Alternatively, mix a little compost in with the potting soil as this helps with water retention and drainage. Also mix in bone meal or an organic fertiliser.
Sowing seed in trays or in small pots makes it easier to care for the plants. When the seedlings are sturdy and about 10 to 15 cm tall then transplant them into bigger containers, with the lowest set of leaves at soil level (this produces a strong plant). Plant only one seedling in each pot, as a single tomato plant will fill a pot as it grows. Putting two or more seedlings together in a pot means they have to compete for nutrients. Also, more than one plant results in dense, overcrowded growth that does not allow in air or sun and the plants thus become susceptible to fungus.
Parsley, oregano, marjoram and basil (if it is pinched back regularly) can be planted along with the tomato plant. These herbs are also good insect repellents. Bark chip mulch will act as a buffer against the sun and keep the roots cool.
Feeding and watering
Vegetables in pots need more frequent watering and feeding than their counterparts in the ground.
•Watering is of the utmost importance. To determine the frequency of watering do the knuckle test every day. This involves pushing your finger into the soil up to the middle knuckle and feeling the soil. If the soil feels almost dry then water the plant, if it is moist to wet then delay watering to the following day.
•A tomato growing in a large pot will benefit if it is given a liquid feed every two weeks. This helps to replace the nutrients that leach out. Feeding can be stepped up to once a week when the plant starts developing fruit.
All potted tomatoes, both determinate and indeterminate, benefit from staking. For indeterminate tomatoes it is best if the trellis is fixed onto a wall. As the plant grows, tie the stems onto the trellis, making sure that you fan the growth out where possible. When you feel the plant has reached its maximum manageable height then pinch off all the growing tips.
A novel way to stake a determinate tomato is to stake the main stem, and then as the side stems are produced to stake them individually so that they are also growing upright. This opens up the plant, exposing all the flowers and fruit to the sun.
Plastic covered steel frames are also available. These must be securely anchored in the soil for them to provide a framework for the tomato. Use plastic or cloth ties (never wire) to secure the stems to the stakes or trellises.
•Tomato plants that dry out in their pots will be susceptible to red spider mite, so be sure to keep the plants properly watered. Keep a watch for red spider mite infestations; if they appear then spray immediately with Ludwig’s Insect Spray, drenching the underside of the leaves. The canola oil in the spray should smother the spider mites. If the infestation is too bad it may not be worth saving the plant.
•Once the fruit starts to form prevent bollworm and caterpillar damage by spraying with an organic insecticide, like Ludwig’s Insect Spray or Margaret Roberts Biological Caterpillar Insecticide.
•Whitefly is always a nuisance and tends to develop a resistance to pesticides. Using a product with a smothering action (those that have oil as an active ingredient) is probably the best option.
•To prevent fungal infestations, keep the containers in an area where there is some air movement. Water the base of the plant and where possible don’t wet the leaves. If the growth is too dense, thin out some of the leaves.
Indeterminate tomatoes have an indefinite harvesting period; keep on picking and they will keep on producing. By comparison, determinate tomatoes have a limited harvesting period and by the time the last tomatoes are picked the plant is exhausted and ready to be pulled out.
Pick most of the tomatoes as they just begin to change from orange to red because leaving them on for longer stresses the plants. It is worth leaving some fruit to ripen completely on the plant because this produces tomatoes with the best flavour. Ripen picked tomatoes at room temperature and out of direct sunlight. Don’t store them in your refrigerator because the cold causes them to lose flavour and texture.