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Grow at Home: how to grow watermelons from seed

Written by Sarah Talbot

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Posted on 1 February 2021

Are watermelons easy to grow?

Watermelons are super easy to grow and require well-drained soil, water, sun and patience as they need a long growing season – at least 80 days. For growing watermelons in the UK, to get the temperatures needed for germination the best time to plant watermelon seeds 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.    

Alternatively watermelons could be grown in a greenhouse or a Grower Frame the benefits of this would enable you control the temperature, light and moisture levels required for germination and plant growth. Then once your watermelons have grown large enough they can be transplanted into the garden. 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 variety of watermelon should I choose to grow?

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!

Can I grow a watermelon from the seed of one I have eaten?

If you eat a particularly delicious watermelon and are inspired to grow watermelons from seed next year then simply save the seeds.

Store watermelon seeds in a cool, dark, dry place in an airtight container to keep out moisture and humidity. They will last for about 5 years stored this way.

Bear in mind that if you plant saved or fresh watermelon seeds the resulting melon, like many fruits, may not be the same type of watermelon you ate and enjoyed.

Where is best to grow watermelon?

The watermelon plant is a vine which is pretty vigorous once it get going and is usually grown in the ground. Did you know growing watermelons in containers is possible too though?  You need a large container but if it is large enough watermelons grow well in pots.

Wherever you grow them, 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.

How do you sow watermelon seeds?

To give your watermelon seeds the best start sow them into Rootrainers in early May (the earlier the better if you have space for the growing plants). Rootrainers allow the first roots race down the special grooves and quickly emerge through the drainage holes. The tips die off naturally causing masses of side roots to develop higher in the cell. This results in a super root system all set to feed the perfect plant. Rootrainers also have a hinged design which allows the plant to be removed without damaging the root system.


Fill rootrainers 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.

How do you plant out watermelon seeds?

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.  

How do I care and harvest watermelon?

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.

How can you tell when a watermelon is ripe?

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!

 

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