How to grow heirloom tomatoes, and when to sow them

What an heirloom tomato actually is

An heirloom is an open-pollinated variety that has been grown and saved and handed on for long enough to have a reputation, and the reason they taste the way they do is that nobody bred them to survive a fortnight in a truck. Modern supermarket hybrids are selected for uniform ripening and thick skin so they travel, and heirlooms were selected for flavour by people who were going to eat them that week, which is also why they split, crack and look a bit rough. If you can put up with an ugly tomato you get a much better one.

When to sow, which is the part most people get wrong

Tomatoes are frost tender and they will sit and sulk in cold soil rather than grow, so timing matters more than almost anything else you do. Sow seed under cover in late winter, in a seed tray on a warm windowsill or in a little greenhouse, and give them 6 to 8 weeks to get to transplanting size. Plant them out in spring once the frost risk has genuinely passed and the night temperatures are staying above about 10 degrees, which is usually somewhere from the middle of October around here rather than the first warm day in September. A plant put out three weeks early will be overtaken by one put out on time, every year.

Varieties worth starting with

• Grosse Lisse. The one half the gardens in the state are growing, and for good reason. Big, reliable, and it keeps producing for months.
• Rouge de Marmande. A ribbed, meaty tomato that copes with heat better than most and ripens early enough to beat the worst of it.
• Oxheart. Large, low-seed and heavy-fleshed, which makes it the one to grow if you are cooking rather than slicing.
• San Marzano. The paste tomato, so if you have any intention of making a sauce, grow this one and grow a lot of it.
• Red cherry. The easiest of the lot, the most forgiving of uneven watering, and the one that gets eaten before it reaches the kitchen.

Soil and spacing

Tomatoes are heavy feeders, so dig plenty of compost or aged manure through the bed a few weeks before you plant rather than on the day, and add some potash, which is what drives flowering and fruiting rather than leaf. Give them at least 6 hours of direct sun. Space them 60cm to 80cm apart, which feels ridiculous when you are planting a 150mm seedling and stops feeling ridiculous in February when the air cannot move between them and everything has fungal spots on it. Put the stake in at planting time, because driving one in later goes straight through the root ball.

Watering, and the mistake behind most tomato problems

Water deeply and on a rhythm rather than lightly and whenever you remember, because almost everything that goes wrong with a tomato traces back to the water going up and down. Twice a week with a good soak is better than a daily splash, and mulch over the root zone holds it steady between waterings. Water at the base rather than over the leaves, since wet foliage overnight is an invitation to fungal disease.

The problems, and what is actually causing them

• Blossom-end rot. The sunken black patch on the bottom of the fruit. It is a calcium problem, but almost never a calcium shortage in the soil, and it is the plant failing to move calcium up to the fruit because the watering has been erratic or the roots have been damaged. Even watering fixes it. Crushed eggshells will not, because they take years to break down, and that is the most repeated piece of bad tomato advice going.
• Splitting and cracking. A dry spell followed by a big drink, so the fruit swells faster than the skin can stretch. Same fix, which is steady water and a good layer of mulch.
• Flowers but no fruit. Usually heat. Tomatoes stop setting once it gets much over 32 degrees, so a run of hot days in January costs you a truss or two and the plant picks up again afterwards. Shadecloth over the top through a heatwave helps.
• Aphids and caterpillars. Squash what you can see, let the ladybirds do the rest, and keep any spray to the evening once the bees have gone home.

Picking them

Pick when the colour is even and the fruit gives slightly under a gentle squeeze, and if birds or fruit fly are getting to them you can pick at first blush and finish them on the bench with no real loss of flavour. Keep them out of the fridge, because below about 12 degrees the compounds that make an heirloom worth growing break down and you end up with an expensive supermarket tomato.

Shop related products

• D.T. Brown Tomato Grosse Lisse 75 Seed Pack. The reliable all-rounder to start with.
• D.T. Brown Tomato Red Cherry 75 Seed Pack. The most forgiving one in the range.
• Brunnings Potash Power 2.5kg. Feeds flowering and fruiting rather than leaf.
• PowerFeed 600ml. A liquid feed for through the growing season.

Did you know we also stock tomato seed in Rouge de Marmande, San Marzano and Oxheart, tomato food tablets, tomato dust, seed raising mix and garden stakes from 900mm up to 1.8m, and the seed and the stakes are not on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

More from the garden centre

The seed, the feed and the stakes all come out of the garden centre, and if you are deciding between two varieties, come in and we will tell you which one people keep coming back for.

Keep reading

• How to grow vegetables that are perfect for the South Australian climate
• The ultimate guide to growing climbing beans with ease
• Seven secrets to growing crunchy carrots in any soil

I grow more tomato plants every year than two people can possibly eat, and I have absolutely no plans to stop.

Candeece