4 simple tips for growing tomatoes in a polytunnel

Homegrown tomatoes have a special place in my heart.

The strong, sweet ‘green’ aroma that fills my nostrils whenever I enter a humid glasshouse filed with tomatoes evokes nostalgic childhood memories of my grandfather’s greenhouse.

I also hold tomatoes sacred as they were the first crop I grew ten years ago.

I was disappointed with the failure to grow tomatoes outside last year. It’s difficult to produce an outside crop here in Wales as the summers are often wet and lack the sunshine required to ripen the fruit. That’s if I can keep them in the ground long enough before they fall to blight.

However, I’m thrilled to grow tomatoes in my new polytunnel in 2018. If I care for them correctly, the protection and extra warmth offered by the tunnel should provide for a wonderful crop later this summer.

As with everything thing I grow, I spend hours researching ways to make sure I do everything possible to produce the best results.

I’ve prioritised four key things to do to get the best results from my tomatoes. The good news – they’re not complicated.

String and tops of tomatoesTomatoes are easily supported by string

Grow up string

Many gardeners grow tomatoes up bamboo canes but I find they have a fairly short lifespan before they deteriorate and break. Therefore, I’m using string to support my tomato plants in the polytunnel this year.

String is relatively inexpensive and if you buy natural twine, like these from Twool, it’s completely biodegradable. At the end of the season, you can place the used string on the compost pile for it to rot down with the other organic matter to be used to feed future crops in your garden.

It’s also very easy to use as a support for tomato plants.

I searched the internet and discovered a number of ways gardeners use string to support their tomato plants. Some pull the string taught and use clips to hold the plants onto it, but the easiest way is to simply twist the string around the tomato plant as it grows.

Twist string around tomato plantAs the plant grows, twist the string around the stem

There are also a number of ways to set up the strings. Charles Dowding demonstrates his method in this video of burying the bottom of the string in the ground, beneath the plant, and attaching the other end of the string to the top of the polytunnel.

The urban farmer, Curtis Stone, attaches the string for his tomatoes to a short bamboo cane placed next to the plant before tying the other end to the top of the polytunnel.

I’ve simply tied the end of the string around the stem at the base of the plant and the other to the pole across the top of the polytunnel.

Remove tomato side shootsSide shoots are the growth that appears in the crotch between the stem and a branch

Remove side shoots

How you prune or train your tomatoes will depend on your choice of variety and how it naturally grows.

Tomatoes have two main types of growth habit: indeterminate (vine or cordon) or determinate (bush) tomatoes. If you grow a determinate variety, don’t remove any side shoots as this will reduce the crop.

However, if like me you are growing indeterminate varieties of tomato, it’s recommended you remove the side shoots as they emerge so that the plant’s energy can be used and kept for growth in the main stem and trusses.

Now you could add these side shoots to the compost pile, or you can actually plant them on and get more tomato plants for free. Tanya over on Lovely Greens demonstrates how to do this in this blog post.

Watering tomatoes
It’s essential to water consistently


Whether you grow the plants directly in the ground or in pots like me, watering is important. The essential element of watering tomato plants is consistency.

They are thirsty plants and as we go through a hot a dry spell here in the UK, my pot grown tomatoes require watering daily. If you allow the plant to go from extreme dry-out to soaking wet, it can cause the fruit to split.

Feed and watering can
Tomatoes require a good feed to provide them with their needs


I don’t use feed or fertiliser on my crops that are grown in the beds of the allotment. It’s an extra expense and I think unnecessary.

Growing using a no-dig approach means every year the beds are mulched with a layer of compost. This provides adequate nutrients for the crops for the entire year.

However, tomatoes are heavy feeders and I’m growing the plants in pots this year. They will require a good feed to provide them with their needs and produce a strong crop.

The team at Envii asked if I’d like to try their organic liquid seaweed fertiliser. The seaweed used in SeaFeed Xtra, Ascophyllum Nodosum, grows in the harsh Atlantic waters and is known for its ability to stimulate strong plant growth.

Envii explain the seaweed used in the product is harvested between April and October, and therefore the growth hormones and biologically active compounds in the seaweed are at their highest levels.

It’s straightforward to use. Simply squeeze the bottle until the feed fills the required amount in the measure on the top. Add the feed to a watering can, dilute with water and drench the plants every 10 days.

Envii Feed measure

Watering can

I’m drenching my tomato plants with the feed, the product can also be used in the form of a foliage spray. So far, my plants are growing strong and healthy.

I’m excited about my tomato crop this year. I’m reaping the benefits of growing inside a polytunnel and next year, I’ll look for more exciting varieties of tomatoes to try on the allotment.

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(Envii have gifted me the seaweed fertiliser. All words and opinions are my own)

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13 thoughts on “4 simple tips for growing tomatoes in a polytunnel

  1. This is interesting but also sad that it is necessary to grow them inside. I know that it is done all the time. Even here, they are grown inside through winter. It just seems unnatural.

    Liked by 1 person

  2. You may have mentioned it elsewhere but what compost are you using, did you add any fertiliser to it and what size pots are you using. They look bigger than mine and mine are too small, I’m having to water twice a day.

    Liked by 1 person

    1. Hi Jim. It’s standard multipurpose compost with no fertiliser added when potted up. I’m using DIY plastic buckets. They are a good size, durable plastic which should last a few years (minimise plastic waste) and I drilled holes in the bottom. The best bit – they only cost £1 each! Mine are from Wilko but all the stores seem to sell the same size, style and sane price. I’ve noticed if happen to miss a day, the compost still holds some moisture.


  3. I imagine that ventilating the polytunnel adequately will also be essential – especially if your weather is hot and dry, as ours is this week (>25C and dry). As you know, I grow all my toms outdoors, and they usually do pretty well. These days I am using 35-litre black plastic pots, which don’t dry out as quickly as smaller pots.

    Liked by 1 person

  4. I’ve also grown tomatoes similarly here in Tx , but in winter. A helpful trick that I learned was to shake the strings daily to help the blooms set fruit. Much better than just relying on the insects. Usually popping them with a broom handle was enough to make a shower of pollen. Also good that you recommended composting the suckers and not feeding them to cattle, because they can cause nitrate poisoning sometimes. I learned the hard way.

    Liked by 1 person

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