Ever since childhood, the taste of summer has been that of watermelon for me. The juicy, sweet flesh is just the perfect treat on a hot summer’s day.
Knowing that watermelons need warmth to grow, I wondered if it would be possible to grow them in the UK. To my utter delight, my research found that yes, it is.
Here is my guide to growing watermelons in the UK, so you too can have the taste of summer straight from your garden.
Choose The Right Variety
Watermelons love heat, which isn’t something our British summers are necessarily known for. Although in recent years, temperatures have reached new highs, at least for shorter periods.
But to be able to grow watermelon plants here in the UK, you have to choose the right variety that can thrive even in cooler temperatures.
We grow Little Darling F1, which gives you small, but deliciously sweet and juicy watermelons. It can be grown in a greenhouse or polytunnel or outside. We are growing ours in our polytunnel.
Another watermelon variety that can be grown here in the UK is the Mini Love F1, which like the Little Darling has been bred to be grown in our climate. It also produces small watermelons, which have a high sugar content, so will be a hit with any child (and adult).
Growing Watermelons In The UK From Seed
We grow our watermelon plant from seed every year. This has several reasons, firstly it’s cheaper than buying a plug plant. Secondly, we can ensure that the seedling has the best start to grow into a healthy strong plant.
Finally, it’s rather difficult to find watermelon plants for sale. They aren’t your common fruit most gardeners grow.
Watermelons are part of the cucurbitaceae family, which is the same family as squashes and cucumbers. Their seeds look similiar to pumpkin seeds, in size as well as in shape.
Sowing starts in April indoors. Fill a small pot with peat-free compost. Sow one watermelon seed in the pot about 1cm (1/2in) deep. I like to water the pot with compost before sowing the seed, so it won’t move to the edge.
Place the pot on a sunny windowsill or a propagator. Being warm weather lovers, watermelon seeds need around 25°C (or 77°F) to germinate. Keep the compost moist, but not wet.
Like their cousins, the pumpkins and courgettes, watermelon seeds germinate quickly, in about a week. After germination, it’s time to repot the seedling into a bigger pot. Keep doing this until it can be planted into it’s final position.
Make sure you water the watermelon seedling sparingly as it grows. You don’t want the soil to dry out, but you don’t want the soil to get too wet either.
Planting Your Watermelon Out
Whether you grow your watermelon under cover or outside, it’s vital that you wait for the right time to plant them out. Watermelons can’t tolerate frost, and won’t survive it.
Growing Watermelons Under Cover
If you’re planning to grow your watermelon in a greenhouse or polytunnel, the right time to plant it out is probably in May, depending on how cold the nights get. You want temperatures not to get lower than ideally 10°C (50°F), but certainly not below 5°C (41°F).
Watermelons are hungry plants, so make sure you prepare the soil well before planting them. We add a layer of homemade compost, any well-rotted organic matter will do, on our beds in autumn. We don’t dig it in, as we have a no-dig garden.
Throughout winter we water the beds with liquid fertiliser we get from our womery. We dilute it 1:10 with water and add it to our beds about three to four times over winter.
Why do we do this? Worm tea, as this fertiliser is called, is THE superfood for plants. Not only does it contain lots of nutrients, but also beneficial microbes, so-called probiotics. (Yatoo et al., 2021)
These microorganisms are necessary for a healthy soil, which, as we all know, is the basis of healthy plants. Having a large number of diverse microbs in the soil will ensure your plants can grow strong and healthy and produce a good yield.
But that’s not all. The worm liquid fertiliser has another secret weapon to help your plants grow better. The worms release a substance that kills off pathogens, i.e harmful microorganisms. (Alkobaisy et al., 2021)
This substance is in the compost you get from your wormery and in the liquid feed. If you use it in the way we do over winter, this useful substance will get into your soil, where it will keep harmful mirobes away, keeping your plants healthier. Isn’t that amazing?
In Spring, we add a layer of our leaf mulch, to supress weeds and add more nutrients that are released slowly as the mulch decomposes. The mulch also keeps the soil warmer, perfect for growing melons in.
You also need well-drained soil, because the roots of the watermelon won’t like wet soil.
Once you have planted your watermelon, water it regularly to help the roots to establish well in their new home.
Growing Watermelons Outside
If you have decided to grow your watermelon outside, make sure you wait until any risk of frost has past. In the UK this is normally in June, depending where in the country you are. The soil needs to be prepared well to make sure there are plenty of nutrients for your melon plant.
You want a sunny, sheltered spot for your melon to make sure it gets plenty of warmth and sunlight.
Before you plant your melon out, you have to acclimatise the plant to the outside temperatures. This process is called hardening off and means that you put them outside for a few hours during the day before planting them out.
Start off with only one hour per day and gradually increase the time they spend outside.
It’s something you do with other plants too, like tomatoes. About a week or ten days should be the right time for your watermelon plant.
Once planted out, water it well and keep watering it regularly until well established.
If you want to grow more than one plant, whether in a greenhouse or outside, make sure you give them enough space. The seed packet will tell you exactly how much space between plants you have to allow.
But generally, about one metre (39in) should be a good distance. We only grow one though, because we don’t have space for more in our polytunnel, because we grow so many different veg plants.
Caring For Your Watermelon Plant
Watermelons aren’t more difficult to grow than tomatoes, but you need to take good care of them.
Support And Training
If you want to save space and grow them upwards, you need to provide them with support and train them.
My preferred support method is the wigwam. All you need is a few bamboo canes (at least three) and some string. Once you have planted the watermelon, arrange the canes, I would use five for watermelons, around the plant.
Tie them together at the top with the string. As the plant grows, attach the stem to one cane. It won’t cling to it itself, so you have to keep tying the stem to the cane the taller it grows.
Once the fruit get bigger, they will need their own support. I have read that people use old bras to make little hammocks for the watermelons. I used pieces of old towels. Just attach them to the support so that the fruit can rest in it.
You can also just let the stems sprawl on the ground, which is what I have started to do. That’s much easier, because you don’t have to tie in the stems and the fruits lie on the ground, so don’t need supporting
Pruning
Once it has grown five or six leaves, pinch out the top, as you would with runner beans or tomatoes. It will also grow sideshoots, which you need to thin out. You want to allow only four to grow.
Train these onto the other canes in the wigwam and pinch out tops once they have grown five or six leaves.
Pruning will encourage the plant to focus on growing fruits, like it does with tomatoes, and needs to be done whether you have trained them to grow up or let them sprawl on the ground.
Watering And Feeding
Watering is vital when growing watermelons in the UK. After all, their fruit consists of 93% water, and this water has to come from somwhere. Watering becomes especially important once fruits have started to form.
We water our watermelon plant every day, as we grow it in our polytunnel. If you grow yours outside, watering needs to be adjusted acording to the weather. If it rains all day, there is no need to water your melon plant.
During prolonged dry and hot weather, you might have to water your watermelon more than once a day. We had a spell of really hot weather, with temperatures passing 30°C (86°F) on several days.
I went into the polytunnel and gave the watermelon some water in the morning, to make sure the soil didn’t dry out. Then in the evening I watered it as normal.
It’s also important to have a watering routine, because most plants, including watermelons, like an even moisture level. This is easily achieved by always watering your plants at a similiar time.
Feeding is equally important, because the plant needs a lot of nutirents to grow these sweet and juicy watermelons. Once the furits have started to grow, feed once a week with a high-potash liquid feed. This tomato feed works well and I have used it for years.
- Easy to apply simply mix with water in a watering can according to instructions
- For tomatoes and flowering pot plants
- With seaweed extract for maximum growth and better crops
If you have a wormery, like we do, just use the liquid fertislier you get from it. As we have already said, it’s a super feed. I only use this now to feed my veggie plants.
Harvesting Your Juicy Watermelons
This is the best bit of growing melons, because you get the reward for the time and effort you’ve put in. But you’ll need some patience, because watermelons grow very slowly.
The Little Darling F1 takes about four months from sowing to harvesting. But it’s worth the wait. And don’t get impatient, because if you harvest the fruit too early, it won’t be as sweet and flavoursome. We have learned this the hard way in our first year of growing watermelons.
There are three tests you can do to check if your watermelon has fully ripened.
- Knock at it – if it sound hollow it’s ready to harvest
- Stab your fingernail into the skin – if it leaves a dent, it’s not yet ready
- Look at the underside – if it’s yellow, it’s ready (only works if fruits lie on the ground)
You can also check the seed packet, which will give you an indication on when to harvest. But it’s still good to check using one or all of these tests. There is nothing worth than the dissapointment of opening a watermelon just to find it’s not yet ripe.
Pests And Diseases Affecting Watermelons In The UK
Growing watermelons in the UK successfully mostly relies on caring for them the right way, but diseases and pests can thwart your efforts. So it’s good to know what to look out for.
Dieseases
As part of the same family as cucumbers and squashes, watermelons are suceptible to the same diseases.
Downey mildew
This fungal disease occurs in wet, cold weather. So if you grow your watermelons under cover, it’s less likely to be an issue.
The first sings of this disease are yellowish spots, angular in shape, on the leaves. An infection can reduce the yield of your watermelon plants.
With this disease prevention is the best defense. So take these measures if you grow your watermelons outdoors:
- Keep plants well spaced to ensure good air circulation which helps dry out leaves quickly
- Plant in a spot that gets maximum sunlight so that the leaves can dry out quickly after rain
- Keep the bed as weed-free as possible, which will help your plants drying off quicker
- Water from underneath to keep the foliage dry
- Look for disease resistant varieties
- Practice crop rotation to prevent a build up of the disease in the soil
If you spot any signs, remove affected leaves immediately and dispose of them, but not on your compost heap.
Powdery mildew
This fungal diseases thrives in warm weather and the first sign of an infection is a white, powdery layer on the leaves. This can lead to a reduced photosynthesis, which is the plant’s way to make food from sunlight.
The good news is that this disease tends to affect older plants that are at the end of their cropping season and start to become naturally weak.
To prevent powdery mildew affecting your watermelon plant, make sure it has enough space around it and isn’t planted too close to other plants. This will help to improve air circulation and access to sunlight.
If you spot a leaf with any signs of the disease, remove it to stop it from spreading to other parts of the plant.
The fruits of a plant infected by powdery mildew are still edible, but they might lack flavour, because the plant can’t turn as much sunlight into sugar through photosynthesis.
Cucumber mosaic virus
This viral disease is transmitted through aphids, who suck the sap of the stems and leaves of watermelon plants. The first sign of an infection are leaves that become wrinkly and brittle.
There will also be yellow or dark green patches on them. The fruit will grow defromed and will have a bitter taste, so aren’t really edible.
Because the virus stops the plant from functioning normally, it will stop growing and you’ll have a reduced yield.
As the disease is transmitted by aphids, you have to keep these little sap suckers away from your plants to keep them healthy. Here are some things you can do, without reaching for chemical pesticides:
- Use companion planting to repel them – strongly scented herbs such as basil are ideal and they will grow well in a polytunnel or greenhouse
- Encourage their natural predetors to your garden – insects such ladybirds, lacewings, and hoverflies will help you to keep aphids under control in your garden (remeber to open the door to your polytunnel or greenhouse)
- Cover young plants with insect mesh – this will protect them from aphids during a stage when they are vulnerable
If a plant does get infected, remove it and dispose of it , but not on your compost heap.
Pests
When it comes to pests, the usual suspects are indicated. Slugs and snails love most plants. They are especially keen on young plants, so make sure your watermelon plants are big enough not to attract too many of these slimy customers.
You can put copper rings around younger plants to keep them away, but once the plants start spreading these won’t work any more.
As we have already said aphids can become an issue. While they themselves are unlikely to cause much harm, unless it’s a heavy infestation, they can transmit the cucumber mosaic virus, which is an issue.
We have already explained how to keep aphids away from your watermelon plants.
Another pest that is mostly an issue when growing watermelons under cover are red spider mites. They don’t like wet weather, so will seek out dry envrionments like greenhouses or polytunnels.
The same measures to keep aphids under control will also work for these little red bugs.
So here you have it, all you need to know about growing watermelons in the UK successfully. Just give it a go, you’ll be surprised at how tasty your homegrown watermelons will be. Happy Growing!
