How to grow Tomato in New Zealand

Where to plant

Choose the sunniest spot you have, with at least 6 to 8 hours of direct sun and shelter from strong wind. Dig in compost and sheep pellets before planting. Tomatoes dislike cold soil, so there is no gain in planting early into a cold bed.

Rotate your beds. Tomatoes, potatoes, capsicums, eggplants and chillies all belong to the same family, so do not plant any of them where one of them grew last season. Leaving three years between tomato crops in the same spot is better still.

• Northland and Auckland: sow seed under cover from mid August and plant out from October once the soil warms. Coastal gardens can plant from September.
• Waikato, Bay of Plenty, Wellington and Nelson: plant out in October and November once the frosts are over. Labour Weekend is the usual guide.
• Central North Island: plant out from mid November, and keep cloches handy for cold plateau nights.
• Canterbury, Otago and Southland: plant out in November or December, in the warmest spot or in a glasshouse or tunnel house. Choose early-maturing and cherry types, which ripen before autumn.

Choosing a variety

• Tall (indeterminate) types such as Money Maker, Sweet 100 and the heirlooms Black Krim and Mortgage Lifter grow 1.8 to 3 m tall and keep fruiting until the cold weather. They need tall stakes and their side shoots pinched out.
• Bush (determinate) types such as Roma grow 0.5 to 1 m tall, ripen their fruit over two or three weeks, and need no side-shoot removal. They are good for sauce.
• Dwarf and trailing types such as Russian Red and Tumbling Tom suit pots and hanging baskets.
• Beefsteak types give big slicing fruit for summer sandwiches but need a long warm season, so they are best in the north or under cover in the south.

How to plant

1. Sow seed 5 mm deep in seed-raising mix indoors in a warm, bright spot, about a month before you plan to plant out. Pot seedlings on when they have two sets of true leaves.
2. Harden seedlings off by putting them outside for a few hours a day for about a week.
3. Put the stake in first, so you do not damage the roots later.
4. Plant in the early morning or late afternoon, setting the seedling a little deeper than it was in the pot so the bottom few centimetres of stem are buried. Roots form along the buried stem.
5. Water in well and mulch with pea straw, keeping it clear of the stem.
6. Tie the main stem loosely to the stake as it grows.

Watering and feeding

Water deeply and regularly at the base of the plant, not over the leaves. Uneven watering, with dry spells followed by a big soak, causes split fruit and blossom end rot. Mulch helps keep the soil evenly moist.

Tomatoes are heavy feeders. Dig compost or a tomato mix into the bed at planting, then feed regularly through the season. Once flowers appear, use a tomato food that is higher in potassium, which helps fruit set. Too much nitrogen gives big leafy plants with little fruit.

Pruning and care through the year

• On tall types, pinch out the laterals, the side shoots that grow between the main stem and a leaf. This keeps energy going into fruit and lets air move through the plant. Neatly snipped laterals can be struck as cuttings.
• Bush types can be left to sprawl, though a short stake or cage helps in windy spots.
• Check the undersides of leaves weekly from late spring for the tomato/potato psyllid. Fine insect mesh over a frame keeps it off.
• Pull out and bag any plant whose growing tips turn yellow and stunted, with cupped leaves and dropping flowers. These are signs of psyllid yellows, and the plant will not recover.
• Remove yellowing lower leaves that touch the soil, to help keep leaf diseases away.

Harvesting

Pick when the fruit is plump and fully coloured for its variety, twisting it off at the knuckle on the stalk. Tall types crop for weeks, so pick every few days.

Tomatoes keep ripening after picking. In a cool or wet autumn, pick fruit as it starts to colour and ripen it on the bench. Store picked tomatoes at room temperature, not in the fridge, for the best flavour.

Growing in pots

Use a pot at least 40 cm wide and deep for a full-size tomato; cherry and dwarf types such as Tumbling Tom cope with a smaller pot of about 30 cm. Fill it with a tomato or premium potting mix, give tall types a stake, and water often, as pots dry out quickly and uneven watering causes blossom end rot.

Saving seed

Heirloom (open-pollinated) varieties come true from saved seed. Scoop the seeds from a ripe fruit, let them ferment in a little water for two or three days, rinse, dry on paper and store in a cool, dry place. Seed from hybrid (F1) varieties will not grow true to the parent.