Time for tomatoes

JANE WRIGGLESWORTH
Last updated 08:30 07/09/2012
Tomatoes
Hybrid tomatoes are a cross between two genetically different tomato varieties. A plant breeder takes pollen from one tomato variety and pollinates the flowers of another variety.

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The tomato planting season typically kicks off around Labour Day but you can sow seeds now for an early start.

If you saved your own seed from last year, first determine whether it is from an heirloom tomato or a hybrid. Heirloom tomatoes are open-pollinated. Open-pollinated tomato varieties come true to seed, which means the plants they produce will be identical to the parent plant. They are self-pollinated, and have the same traits from one generation to the next.

On the other hand, seed saved from hybrid varieties will not come true to type. Hybrid tomatoes are a cross between two genetically different tomato varieties. A plant breeder takes pollen from one tomato variety and pollinates the flowers of another variety. He or she does that to combine the desirable traits of one variety with another. For example, a plant breeder may wish to cross a tomato that has good disease resistance with another that is uniform in shape. The two varieties are cross-pollinated and a new hybrid, a uniform disease-resistant tomato, is created.

You may have noticed tomatoes labelled F1. These are hybrids that have parents of two different varieties.

The seeds saved from these hybrid plants, however, are not self-sustaining. They do not keep the same characteristics of their parents. Rather, they usually have an unpredictable mix of characteristics. You can still sow the seed, of course, but if you plant it, do not expect to produce the same tomato that you grew the previous year.

Can tomatoes cross-pollinate? Heirloom tomatoes have a greater chance of cross-pollinating, but even then there is only a 2 per cent to 5 per cent chance of natural hybridisation. In modern tomato varieties, the pistil of the flower does not usually extend beyond the stamens. The pollen spreads on the inside of the flower and thus self-pollinates. However, in many heirloom varieties the pistil extends beyond the stamens, exposing itself to pollinating insects. But tomatoes do not typically attract pollinators as there are usually better pollen sources elsewhere. Hence there is only that small chance of cross-pollination.

If you want to be absolutely certain that the seeds you are saving will grow strictly true to type, you need to plant different tomato varieties at least 30 metres apart. Positioning plants with a rich source of nectar nearby to distract pollinating insects would be beneficial.

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At this time of year I start my tomato seeds off in trays. I like the black oblong seed trays because the shallow depth keeps the soil fairly warm. Once sown, keep trays in a warm spot under cover.

When plants have grown their second pair of leaves, transplant into individual pots to keep plants growing steadily until all risk of frost has passed. Grip them by their leaves rather than the stem, which is easily damaged. If damaged, growth may be inhibited and disease may enter the plant at the injured spot.

Dig plenty of compost into your soil before planting, as well as calcium in the form of lime. Calcium helps to control blossom end root by strengthening the cell walls.

Plant your seedlings out in the garden once all danger of frost has passed and soil temperatures remain above 10C. Harden them off first by gradually introducing them to the cooler outdoor temperatures and greater light conditions. Yellowing leaves soon after transplanting indicates they were not hardened off

Plant them a little bit deeper than they were in the pots. You can even plant them up to their first leaves. Tomatoes develop roots along their stems, and more roots will mean a stronger plant, one that is able to support heavy crops.

Give your plants plenty of space in the garden (at least 40cm apart) to ensure good airflow and to discourage disease.

Insert stakes at planting time so you do not damage roots later. Or use a tomato cage. Bend old reinforcing wire into a cylinder, use tying wire to secure it, then push the ends into the soil over your tomato plant.

Feed plants with a general liquid fertiliser in the early stages of growth to encourage strong, healthy plants. Just before your plants flower, switch to a specialist tomato fertiliser. Tomato fertiliser is high in potassium and encourages lots of flowers and fruit.

Regular watering is particularly important. Lack of or irregular watering can lead to all sorts of problems, including blossom end rot and cracked skins. If planting in containers, watering becomes all the more important, as the soil in containers dries out quickly.

As plants grow, remove the side shoots (laterals). If your plants have too many side shoots, they will put all their energy into growth rather than fruit. Pinch these off with your fingers.

As aphids and other bugs are attracted to the yellow, plant yellow nasturtiums at the base of your plants to lure them away from the main attraction.

Greasy cutworms can be a pest of young plants. They come out at night to munch on the leaves and stems. These creatures are grey-brown when young and dark grey with yellow stripes when mature, and around 4.5cm-5cm long. Spray plants with Kiwicare Organic Caterpillar Bio Control.

When it comes to harvesting, pick your tomatoes when they are fully ripe for the best flavour.

Cherry tomatoes are prone to splitting, especially when overripe. Watch them carefully and pick when just ripe.

- © Fairfax NZ News

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