Growing Organic Tomatoes

Organic NZ Magazine: November/December 2001
Author: Denise Mark

Denise Mark describes exactly how to grow delicious, organic ‘Love Apples’.

Is conventionally grown to your taste?

Imagine a conventionally grown tomato, bred for long shelf life, growing in a plastic bag full of sawdust. Imagine the plant being fed an unrelenting cocktail of calcium, ammonium and potassium nitrates, potassium and magnesium sulfate and potassium sulfite. Imagine chemical sprays dripping from its leaves, killing the pests and diseases attacking it. Now imagine buying this tomato from the supermarket and eating it!

… Wonder why things don’t taste like they used to?


History of tomatoes

Tomatoes grow wild in the Peruvian Andes and were first domesticated in Mexico and Central America. It’s hard to believe that Europeans initially regarded them as poisonous and grew them as ornamental plants. However, by the end of the 18th century they were widely used in cooking and salads. Although classed as a fruit, they are the second most popular vegetable in New Zealand, and give a higher yield for the amount of space than any other.


Tomato varieties

If you buy tomatoes from a supermarket you may think that only three types exist: large beefsteak, medium-sized salad, and cherry tomatoes. All are red, smooth and round. In fact, tomato colours range through red, pink purple, orange, green and yellow. Some varieties such as Tigerella are striped or splashed with a contrasting colour. There is a huge variety of shapes and sizes, from huge beefsteak to minute currant, and oval and tiny pear-shaped tomatoes. Some are solid; others almost hollow, bitter or sweet and have numerous culinary uses. Tomatoes also vary in their leaf shape, their ability to set fruit in cold conditions, and resistance to disease. In the mid-1990s over 600 varieties were commercially available in the US and Canada, and 2500 varieties kept as seed in the gene bank in Gatersleben Germany.


Heirlooms or hybrids?

Commercial growers purchase hybrid tomato seeds, bred for long shelf life, high yields, uniform ripening, disease resistance, easy picking and freighting. Flavour is not considered important. However, for most home gardeners, taste is a prerequisite. Home-grown tomatoes taste better because they can be left on the vine until needed, thus ensuring higher sugar content and better flavour. Tomatoes grown in healthy living soil without artificial pesticides and fertilisers also have a higher and more balanced nutritional composition.

Heirlooms usually have a flavour superior to commercial varieties, plus an infinite diversity of shapes and colours. However, some may have lesser resistance to a particular disease or a tendency to crack, split or just look odd. Planting a mixture of heirloom and hybrid seeds generally works well.


SIXTEEN KEY STEPS for successful tomatoes

1. Choose varieties carefully
Carefully choose the variety of tomato to grow. Research what varieties do well in your area. Some such as ‘Oregon Spring’ fruit in cooler conditions. In more humid areas grow varieties with proven resistance to fungal diseases. Decide if you want to purchase organic seed, hybrid or heirloom varieties, early or late harvesting varieties.
Tomato varieties are classified as determinate or indeterminate. Determinate varieties are bush types, producing one crop rather than a prolonged harvest. Indeterminate, or cordon types, grow on long vines and need staking. If their laterals or side shoots are removed these varieties crop over a long period.

2. Plant your seed
To get a head start sow seeds indoors five to seven weeks before you intend to set out plants – they take around three months to produce well. Tomato seeds germinate best in temperatures of 21° to 24°C during the day and around 16°C at night. Sow as deep as the seed is wide. Keep the soil moist until seeds have germinated.

Use fine loose compost with reasonable drainage, and water-in using chamomile tea to reduce the danger of damping off – caused by an overgrowth of soil-borne organisms. Seedlings should germinate in eight to 10 days and for the next fortnight should be watered from the bottom to inhibit growth of fungal organisms.

When the seedlings form two true leaves in addition to their seed leaves, transplant into individual containers about three inches deep. The objective is to keep them growing rapidly.

You can buy seedlings from your local nursery; but choice will likely be restricted to hybrid varieties. Choose young strong plants, not spindly specimens with flowers or fruit on them. If they’re already starting to flower and fruit, they’ve probably been kept in the seed tray too long and are maturing too quickly – they’ll never reach their full potential and growth will likely be stunted.

3. Choose growing site carefully
Tomatoes are sweetest grown in full sun, but most varieties will produce a good tasty crop even in cool areas. Their main requirements are:
* Open, sunny well drained location. Many tomato diseases are associated with poor drainage e.g. stunting, bacterial wilt and fruit rots.
* Light, free draining soil pH 5.5 to 6.8, high in organic matter. Add peat moss or sand to improve texture of clay soils. Use compost to condition sandy soil.
* Good air circulation to prevent leaf blighting fungal diseases and fruit decay.
* Protection from frost and strong winds
* Temperature for fruit to set is 18°C to 24°C.

4. Prepare your garden bed
A base of healthy soil is the key. Ideally a green manure crop such as lupins, clover or broad beans should be grown over winter and dug into the soil in early spring. Organic beds for tomatoes need lots of compost, natural rock minerals, and excellent drainage. Suitable materials include fallen leaves, household compost, composted cow or horse manure, rock dusts and vermicast. Worms also help aerate the soil. Ideally beds should be raised to promote good drainage and ensure healthy roots. A balanced soil and a healthy population of micro-organisms from organic composted material ensures strong plants with an increased resistance to pests and diseases.

5. Transplant seedlings
Seedlings can be transplanted five to seven weeks after sowing. Transplant only after all danger of frost has passed and transplant only the healthiest looking plants. Reduce transplant shock by minimising disturbance to the roots and soil surrounding them. Add a handful of compost or worm castings to each hole, or water in with chamomile tea. A tablespoon of milk powder also helps ward off fungal diseases.

Set out plants 60 cm apart in rows spaced 60 to 100 cm apart. Plant deeply. Tomatoes sprout roots from the stem, which make the plant more stable.

6. Support plants
Tomato plants have many side stems that break easily if not supported. Most varieties are best trained to one or two leaders to give larger tomatoes and keep them off the ground. Staking also reduces the likelihood of anthracnose and soil rots. Each leader requires its own stake. Tie the plant to the stake with soft yarn or small strips of old cotton. To prevent injury to the rapidly growing stem, attach the tie tightly round the stake and loop it loosely around the plant stem just beneath a leaf node. Plants with several leaders should be supported and trained on a fence or fame – or use a wire cage. Ensure the spaces in the wire are large enough for you to reach through to harvest.

On cold nights cover young plants with inverted baskets or paper bags to protect from late frost damage.

7. Remove laterals
Other than those chosen for leaders, pinch out all remaining laterals (side shoots). To avoid large wounds and minimise disease attack, do this when laterals are small.

8. Mulch
Bare soil under tomatoes should never be exposed. Mulch provides a physical barrier between soil and plant surfaces, protecting from diseases, retaining soil moisture, preventing weeds from sprouting, and keeping roots cool. Suitable mulches include straw, leaves, dried grass clippings or pine needles. A living mulch of marjoram and oregano smells nice, confuses the white cabbage butterfly, and repels insects. Diverse living mulches of lettuce, basil and chives also repel insects and keep down weeds.

9. Use companion plants
Certain herbs and flowers planted near tomato plants improve their growth, repel insect pests and attract beneficial insects. Sprays can also be made from their leaves and flowers to tackle pests and diseases.

Basil is the classic tomato companion. Loved by bees, it repels aphids and whitefly. Tomatoes grown near basil take on their flavour. Basil sprays are useful to repel and sometimes kill whitefly, aphids and spider mites.

Other good companions include:
* Stinging nettles – proven to substantially increase crop yields and reduce fungal attack.
* Nasturtiums – repel aphids, green shield beetle. Also thought to deter/reduce fungal diseases
* Borage, phacelia and lemon balm – attract beneficial insects.
* All the umbilliferae family – celery, parsley and carrots – attract hoverflies to prey on tomato pests. They also feed at a different root zone so are good companions.
* French marigolds deter nematodes.

Other companion plants include thyme, asparagus, celery, foxgloves, lavender, garlic and sweetcorn. Do not plant rosemary, potatoes, kohlrabi, fennel, strawberries and dill near tomato plants. Members of the brassica family often harbour caterpillar larvae.

10. Feed plants
Foliar feeding is best, supplemented by the occasional root feed. The general rule is feed plants once a fortnight prior to fruit set. When fruit is setting, feed once a week, preferably late in the day, as plants feed at night. Suitable foliar sprays include compost tea, fish, molasses, worm rum and seaweed. These strengthen the stem and help plants resist pests and some fungal diseases.

Comfrey, animal and bird manures are suitable liquid fertilisers. Sprinkle a tablespoon of milk powder once a week around the plants and water in to help reduce fungal disease. As long as plants have good colour, pH is fine. If a plant looks a little off colour give it a good feed of liquid fertiliser.

11. Water often and sparingly
A light watering every day is preferable. Watering should be even and regular so as to avoid problems such as blossom end rot, sclerotorium and stem rots. Watering or rain when the fruit is maturing may cause the skin to split near the stem.

Water early in the morning, never in the heat of the day. Do not water in the evening when plants are more prone to fungal attack. Hand, rather than overhead watering, reduces the risk of fungal attack. Water around the roots. Hand watering also helps avoid spreading disease.

12. Pluck the first flowers
Growing deep, extensive roots and a full leaf canopy helps establish newly transplanted tomatoes. Pull off the first flowers (that’s hard, I know) so the plant doesn’t devote energy to forming fruit before roots and foliage have filled out. Do this until plants are at least 30 cm tall. Also remove all shoots from the main stem below the first fruiting branch.

13. Inspect plants daily
Are any parts being eaten? Any change in leaf colour? Do any parts of plants look like they’re dying? Are plants wilting even though watered? Correct symptoms promptly. It doesn’t take long for a problem to get out of hand. Remember, cultural inadequacies, too much water, too little water, and erratic watering can produce symptoms that mimic disease. Promptly remove any dead, diseased and rotting fruit and leaves. Just one leaf attracts pests and more disease. Do not put diseased materials in the compost. Insects and pests always attack the weaker plants first: consider having a sacrificial plant in the hope pests will leave the other plants alone.

14. Know your pests, diseases and disorders
The main pests affecting tomato plants are aphids, whitefly, red spider mites and caterpillars. Tomatoes are also prone to fungal diseases, especially blights and rots. Prompt diagnosis and action is essential. Use the sprays/methods in Recipes for Success p.25. Because tomatoes are heavy feeders, any nutrient imbalance may look like a disease.

Other actions to reduce outbreaks of pests and diseases:
* Regular inspection
* Prompt action
* Ensure good air circulation around plants
* Do not water in the evening
* Control weeds – many harbour pests and diseases
* Keep soil well mulched
* Use companion plants
* Regular feedling with foliar sprays, especially compost tea
* Water regularly and evenly – cracking of fruit, blossom end rot, wilting and dried patches on leaves all resemble disease!
* Good housekeeping, removal of diseased or rotting fruit and leaves.

15. Protect against birds
There’s nothing worse than mentally savouring the taste of your first tomato then watching in disbelief as our winged brothers descend for a meal. Place netting over your plants. Intriguingly, birds do not seem to attack yellow or cherry tomatoes.

16. Save the seed
Only save seed from non-hybrid plants. Tomatoes are one of the easiest crops to save from seed and this is why there is such a wide selection of heirloom varieties. Cross-pollination rarely occurs, except in some of the oldest varieties such as currant tomatoes (Lypopersicon pimpinellifolium). Where cross-pollination might occur, cover flower trusses to isolate them.

Save seed from the biggest and best looking fruit. Leave on the plant until really ripe then cut open and squeeze seeds and gel into a bowl. Leave in a warm place until a layer of mould covers the surface. This smells unpleasant but natural fermentation kills many seed-borne tomato diseases.

After three to four days, scoop off the top fungal layer. Use a sieve and clean water to wash the seeds. Dry in a warm place out of direct sunlight.

Store seeds in a cool dark place with little temperature fluctuation. Keep seeds in paper packets in an airtight container with silica gel crystals. Seeds will keep at least three years. (See also S&H Jan/Feb 01.)