Growing tomatoes outdoors - my top tips

In out, in out, shake it all about - my tomato seedlings get moved indoors and out to harden them off. A washing up bowl makes a cheap, secure carrier.

Back in 2004, the year I started blogging, I was writing about tomatoes. Years later, I am still going on about tomatoes.

This is partly because people keep asking me about them - for some reason beginner gardeners always seem to start with tomatoes, which is a curious choice. On the scale of veg growing difficulty that goes from 1, easy, pea shoots and mustard cress - right through to to 10, extremely difficult, vanilla pods (OK I just invented that scale, but let me run with this...) tomatoes score about a 7, I'd say.

They have a short harvest window, are vulnerable to blight and other problems, and are tender, so have to be toted in and out of the house all spring until it's warm enough to put them outside day and night. And yet I can see their appeal.

Want early tomatoes? Sow an early variety, like this one - Belarusian variety 'Peremoga'. Photograph: Jane Perrone.

I was inspired to grow tomatoes by seeing my grandad John's plants laden with huge beefsteaks, rubbing the furry leaves between my fingers and sniffing their curious scent. When I started growing them myself, I got obsessed with the curious world of heritage tomatoes. If you're interested in finding out more about this - I'd recommend listening to the episode of the Guardian's Sow, Grow, Repeat podcast where Alys Fowler and I talk about tomatoes, including an interview with breeder Craig LeHoullier. 

But rather than waxing lyrical, I wanted to revive my tomato growing advice that's existed in various guises over the life of my blogging, update it and offer it to anyone who's sweating over the state of their tomatoes this spring. So here goes. If I have missed anything, give me a shout in the comments!

Outdoor tomato growing tips*

1. Sow early, but not too early - March or April - in a heated propagator. Sow an early variety if you want the quickest possible harvest (Real Seeds has a good selection of early tomatoes). When you pot them into their own pots, use good quality peat-free compost as this can make all the difference to early growth. The tomatoes you can see above were grown in New Horizon multipurpose peat free: in the last couple of years I have switched to Sylvagrow peat free multipurpose by Melcourt which I find is better quality. If you use a substrate not designated as suitable for seeds, you may need to sieve out larger lumps.

2. The number one error in the month of May is being lulled into a false sense of security by the weather and planting tomatoes out too early. Tomatoes stop growing once the temperature drops below 10-12C at night, and ideally they need 15C in the day. And frost will kill them, so wait til the frost risk is completely over before sending them outside for good - which is the end of May in my neck of the woods, which is southern England). Right now my tomato plants are ensconced in old washing up bowls, as per the picture above, so they can be toted in and out of the house morning and evening to make the most of the sun, but also gain some protection at night. 

3. Make sure you plant the seedlings out deeply - I usually plant to the depth of the first leaf, which I remove - as this helps a strong root system to develop. If you look at the lower stem of a tomato, you'll see bumps. If you plant these below soil level, they'll produce roots. 

Wondering what a tomato truss looks like? Here it is!

4. Add fertiliser as they grow, but not too much: overfeeding can dilute the flavour. Use tomato fertiliser rather than any old fertiliser you have to hand, as it needs to be lower in nitrogen and higher in phosphorous than most all-purpose feeds. I favour regular additions of comfrey tea and Maxicrop seaweed plant food.

5. Remove any shoots that appear between the main stem and leaves emerging from it. Why? These cause the plants to divide their fruiting energy between two stems, weakening the plant and stopping it from producing fruit. If you act quickly, you can turn these cuttings into new plants! Let the sideshoots grow to around 8cm long, then cut them off and pop into a glass of water. Once roots appear and are around 5cam long, pot them up to make a new plant.

There’s an exception to the pinching rule - if your tomato cultivar is a ‘bush’ or ‘determinate’ type, it will not need to be pruned in this way as it’s been bred to grow bushy.

6. I used to advise removing the lower leaves as the plant develops, but the collective wisdom now is that this doesn't really help produce good fruits. If the lowest pair of leaves start to go yellow and the rest of the plant is healthy, cut them away, but don't be too brutal.

7. Water daily if they are being grown in a growbag or container. Rainfall will almost definitely not be enough for plants in containers: if rain is forecast you can help plants absorb the rain by watering first, as already-damp soil will soak up more moisture than hydrophobic soil. Help the water to sink in rather than running off by making a shallow indentation in the soil around the plant - if you really want to ensure the water gets to the roots, when planting out you can sink a plastic bottle, bottom chopped off and cap removed, into the soil next to the plant to act as a funnel. Mulching with newspaper or grass cuttings will also help to conserve water. If your tomatoes are splitting, this is usually a sign that watering is too irregular . Blackened bottoms to the fruits - known as blossom end rot - is also usually a sign of underwatering.

8. Tie the growing stem into a sturdy stick to stop it toppling over, adding new ties as the plant grows: for a large, strong plant this may be as frequently as every three inches.

9. Once four or five trusses have formed, pinch out the main growing stem to halt the plant's growth. That way, the plant will put its energies into producing the fruits already forming rather than spreading itself too thin.

10. The disease blight can be a real issue for outdoor tomatoes. Watch out for black blotches appearing on the stem and leaves: when blight strikes there is not much you can do other than harvest what fruit there is and try to ripen unripe fruits indoors. When watering, avoid splashing water onto the foliage. Growing blight-resistant tomatoes such as ‘Crimson Crush’ will help. More in-depth advice from the RHS here.

11. Pick the ripe tomatoes regularly, taking the time to rub the leaves between your fingers and suck in the delicious tomato plant smell. It's one of a veg grower's great pleasures (also applies to blackcurrant bushes).

What have I missed? I am sure you have loads of tomato growing expertise to share - add in your suggestions below ...