Summer is months away but those who want to grow tomatoes from seed should get started soon, says Gillian Vine.
Although nothing is gained by planting tomatoes too early, those planning to grow them from seed should get cracking this month or the plants will fail to develop quickly enough to give a good crop, as it takes six or seven weeks from germination to transplanting.
The advantage of growing from seed is the large range on offer - one seed company lists 55 varieties, another has 33.
Containers for growing tomatoes from seed can be made from two-litre ice-cream containers with holes punched in the bottom.
Half-fill the pottle with tomato mix, then add a 20mm layer of seed-raising mix. Water so the mixture is moist, but not wet. Scatter seed thinly on top and cover with a 20mm layer of seed mix. To retain moisture, cover with cling film.
Keep in a warm place (18degC is ideal for tomato germination) but not beside a window, where frost outside can kill the tiny plants.
When the seedlings appear, wait until the first true leaves appear, then thin out the plants. At this stage, they can be transferred into peat pots to grow on, but the depth of the ice-cream container and the tomato mix under the seed mix means the plants can be left until they are bigger and stronger before being transplanted.
Plant outdoor tomatoes in a sunny, sheltered place when all danger of frost has past. Even then, it is a good idea to start them under a cloche or cold frame to give them the best chance to develop.
Greenhouse tomatoes can be planted out a little sooner but if in doubt, it pays to wait.
For those who prefer to buy plants, garden centres have begun stocking more varieties, including heritage types notable for their outstanding flavour, although they tend to have smaller crops. Grafted tomatoes are reliable performers, although Australian tests suggest that the crop yield may be smaller than for the same variety grown on its own roots.
Growing tomatoes in pots or bags of commercial mix means they receive the optimum nutrients without wasting the mix. At the end of the growing season, the mix can be tipped on to the vegetable garden to improve the soil.
The other advantage of potted or bagged tomatoes is that outdoor varieties can be moved if the initial choice of site is less than ideal.
Selecting the right tomatoes for your situation is important.
Small varieties, such as Sweet 100 and the somewhat larger Sweet Million, are good for outdoors, although Russian Red, Bloody Butcher and Black from Tula are hardy heritage varieties.
Every glasshouse owner has favourite tomatoes but Taupo, Big Beef and Moneymaker are worth trying.
For a hanging basket, look for Tumbling Tom, which comes in red and yellow forms. The small varieties generally have higher yields per plant.
All tomatoes are acid, with a pH of about 4.3. The so-called low-acid tomatoes have the same pH but a higher sugar content than their tart cousins; the sugar masks the acidity.
Except for dwarf types, tomatoes need staking and stakes should go in when the tomatoes are transplanted, so the root system is not disturbed.
Outdoor tomatoes can be grown against a trellis to which stems are tied.
Even watering during the growing season is important. Tomatoes can put their roots down 1m or more, so deep watering is necessary. As the tomatoes start to ripen, reduce watering and trim leaves so the maximum light gets on to the fruit.
After harvesting, do not put tomato plants in the compost bin.
Diseases
• Stem rot is the most common disease of tomatoes and appears as brown patches on the stems. It can be caused by several different fungi, which is why it is important to grow tomatoes in new soil each season.
• Tobacco mosaic virus (TMV) can be transmitted to plants from smokers' fingers and causes yellow mottling on leaves and uneven ripening. Modern cultivars have been bred to be resistant to TMV but it still appears in old varieties.
• Keeping aphids and thrips out of glasshouses reduces the likelihood of viruses found in potatoes and cucumbers attacking tomatoes. Growing dwarf marigolds (Tagetes types) between tomatoes will help keep whitefly and other pests at bay.
• Blossom-end rot on the fruit is a dark spot at the opposite end to the stem and is an indication that the plant lacks calcium (lime) or that watering is inconsistent. Work dolomite lime into the soil before planting.
Tomato types
• Tomatoes come in two main types, determinate and indeterminate, which refers to the way they grow.
• Determinates stop growing when they have produced a certain number of nodes, while indeterminates just keep on growing, giving sprawling plants that need more pruning by nipping out laterals.
• Except for the compact dwarf types, all tomatoes need some form of support.
