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Grow at Home: the best way to grow Watermelons

Written by Sarah Talbot

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Posted on 1 February 2021

watermelons cut and uncut grow watermelons  in the UK

Watermelons like a warm sunny climate and need a looooong growing season – at least 80 days.  The UK temperature needed for germination means the best time to plant them is late May.  However, if you wait until late May to start them you will risk them not having enough time to ripen. 

So it’s a balance.  If you have the inside space to start them a little earlier then you will have a longer season to play with and a better chance of ripening.  The down side of starting them early is that you will have them taking up space inside until around June when all risk of frost has gone.    

You will also need a bit of gardening kit for these. So, ideally a greenhouse or Grower Frame or at least a Garden Cloche and a Fleece Blanket

Once they get started they are fairly self sufficient though and put on impressive, triffid like growth.  So if you have the space, the only gamble you are taking is that we will have a summer that’s warm enough to ripen them.

Which to choose

2 watermelons in growing the ground  - Haxnicks gardening advice the best way to grow watermelons in the UK

There are some varieties that perform ok in cooler climes so search these out. But beyond that, which variety you choose will depend on

  • the site and the facilities you have, propagator, greenhouse etc.
  • Where you live – you’ll find it easier and need less kit in the Scilly Isles than the Shetlands.
  • And the space you have in your fridge – remember to check the size of the final fruit, some of them are massive!

Where to grow them

The watermelon plant is a vine which is pretty vigorous once it get going but can still be grown either in the ground or in a large container. Whichever you use, watermelons need a well drained soil with a pH of around 5 ½ to 7.  The heavy fruits are difficult to support so it is best to leave them sprawling on the ground or around the container you are growing in. 

They’ll need about 90cm (3 feet) each to spread out. 

Choose a sheltered spot which gets lots of sunshine. Dig in lots of good compost and organic matter to prepare the soil.

Sowing

Watermelons seeds UK

Sow your watermelon seeds in pots in early May (the earlier the better if you have space for the growing plants). Fill the pots with seed compost and sow 2-3 seeds per pot at 1” (2-3cm) deep.

Keep the soil moist and warm – around 21 – 22°C. The seedlings should emerge in 7-10 days. Move to a sunny windowsill to give them as much light as you can as soon as they emerge. 

When they are around 3-4 weeks old start feeding with a 50% diluted houseplant food.

Planting Out

You will not be able to transfer them outside until the ground is warm and all chance of frost has passed.  It needs to be at least 16°C - 21°C (60°F to 70°F) This will probably be around June in the UK but you can bring this forward by pinning down a Fleece Blanket a few weeks before, to warm the soil.

Even planting out in June it is advisable to cover them at night until July.  

After Care & Harvesting

Water the plants well and make sure you allow them to drain properly between watering. they do need water throughout the season, but the most important time to water them is while they are setting and growing fruit. Watermelons are 92% water after all!

If the temperatures are low (one of those summers!) then you might need to take them back into the greenhouse if they are in a container. Or if they are in the ground then you can put them under a cloche, or wrap them in a fleece blanket to give them the conditions they love.

As summer progresses you should see the fruit start to appear and swell. About 2 melons per plant is the norm.

Harvesting

You can tell if they are ripe by tapping the side and listening.  They will sound hollow when they are ready. To harvest them cut the stem with a sharp gardening knife.  Don’t forget to save the seeds to plant next year. 

 

Fun Watermelon Facts

Did you know that watermelons can be haunted?  Well not really, but they can explode and people once believed that this was because they were haunted.  The actual explanation is either they carried an exploding gene found in some heirloom varieties.  Or, they had a bacterial infection inside likely caused by a natural yeast. Either way watch out for haunted watermelons they could make a mess of your kitchen!!  

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