This tomato mistake could ruin your crop – and 5 more lessons pro gardeners have learned about growing tomatoes successfully

I bought three new tomato plants at the weekend, and I’m determined to nurture them into heavy croppers – so I thought I’d start by asking pro gardeners for a list of lessons they’ve learned about growing tomatoes over the years.

Learning how to grow tomatoes is so rewarding, whether you’re starting them from seed or buying young plants like I did. They can be fussy, though – there are certain plants you shouldn’t grow with tomatoes, for example, and a few other conditions that need to be just right to keep the plants happy.

To get our crops off to a flying start, here are six things pro gardeners learned about growing tomatoes successfully.

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1. Don't plant them out too soon

This one worried me a little bit, since I’ve just planted my new tomato plants in pots on my patio – because according to horticultural expert Ross Dyke, who hosts The Plant Pod podcast, spring is still a risky time to plant your young tomatoes outside. In fact, rushing it could ruin your crop.

‘One of the biggest lessons I’ve learned with tomatoes is that timing really matters,’ he says. ‘It’s so tempting to rush them outside at the first sign of sunshine, but tomatoes absolutely hate cold nights and chilly soil. I now always wait until the risk of frost has passed and nighttime temperatures are sitting around 10℃ before planting them out.’

You’ll also need to harden your plants off before you keep them outside permanently.

‘I always harden plants off properly over seven to 10 days before they go outside,’ says Ross. ‘It sounds simple, but gradually acclimatising them to wind, cooler temperatures and direct sun really reduces transplant shock and helps them establish faster.’

You could order a soil thermometer like this one from Amazon to double-check the temperature of your soil, just to be on the safe side.

Ross Dyke

Ross is Hornby George PR’s resident horticultural expert, bringing hands-on growing knowledge alongside a strong track record in education, media and industry engagement. Alongside his work as a grower, he hosts The Plant Pod podcast and founded Get Children Growing – an initiative that has delivered more than 14,000 free grow kits to UK schools in just two years. His first book, The School Garden Guide: How to Grow, Cook, and Learn, is set for publication this September.

2. Preparation matters

Another thing pro gardeners like Ross learned about growing tomatoes successfully? It’s all about the work you do before planting – in fact, preparation is the very foundation of how well your plants will perform.

‘I’ve learned that preparation makes all the difference,’ says Ross. ‘I plant tomatoes deeply, and enrich the hole with compost.’

It’s worth looking into the best soil for tomatoes, too. I’m currently using Dalefoot Peat-Free Wool Compost for Tomatoes, which you can buy from Crocus, which has enough nutrients to feed the plants for the whole season. You can either use the bag as a grow bag for two tomato plants or use the compost in pots (which is what I'm doing!.

If you’re using regular compost, though, fertiliser is very much something you’ll need on your radar…

3. Feeding = stronger plants

If you want your tomato plant to produce loads and loads of harvests, you'll need to have some fertiliser to hand.

'Once you see the first flowers, start using a proper tomato feed,' advises Julian Palphramand, head of plants at British Garden Centres. 'If you use a general-purpose one, you’ll get lots of leaves but very little fruit to pick.'

The most popular tomato fertiliser is Levington Tomorite, which you can buy from Amazon, but Ross recommends Envii Maximato Xtra, which you can buy from B&Q.

'It’s specifically formulated for tomatoes, and I’ve found it brilliant for encouraging stronger growth, more flowers and healthier fruit,' he says. 'I use it every seven to 10 days once plants are established and honestly wouldn’t grow tomatoes without it now.'

There's also the best type of fertiliser for ripening tomatoes, to keep the plants pumping out ripe fruit all summer long.

4. Watering requires balance

Tomatoes in grow bags and pots will need watering more regularly, since they'll dry out quickly in hot weather. You mustn't overdo it, though.

'If you want a decent crop of tomatoes, you have to get your watering right,' says Julian. 'The biggest mistake is letting the pots dry out and then drowning them to make up for it; that’s exactly how you get split skins and rot.'

It's also about where you water your tomatoes – and I know I've been guilty of hitting the wrong spots with the watering can.

'Make sure you water the soil, not the leaves,' warns Julian. Wet leaves are a breeding ground for plant diseases.

5. It's wise to pinch out the side shoots

Every gardener who wants a good crop should know how to pinch out plants, especially when it comes to plants like tomatoes and sweet peas. It’s one of the most important things Julian learned about growing tomatoes.

‘You can’t be shy about pinching out the side shoots,’ he says. ‘If you let every little shoot grow, you’ll end up with a massive green bush and no actual fruit. Get rid of them early so the plant focuses on the tomatoes.’

You can pinch off the side shoots using your finger and thumb – it's as simple as that!

6. Supports are key

Last but by no means least, Ross tells me that investing in some good plant supports is key to supporting tomato plants – especially if you’re growing cordon plants, which get pretty tall.

‘Support is another thing people often overlook,’ says Ross. ‘Get canes or stakes in early before roots spread too far, otherwise you risk damaging the plant later on.’

So, if you're just about to put your tomato plants outside, it's best to put supports in place at the same time. This grow bag frame from Gardening Express is brilliant for supporting plants in grow bags, but for pots and vegetable beds, you'll want to go for something like this Garden Gear circular tomato support frame from Thompson & Morgan.

I'll be taking these tomato lessons on board for the rest of the season. I've got some tasty tomato varieties on the go!