Watermelons are great fun to grow! If you’re wondering whether we can grow these delicious fruits in the UK, the answer is yes we can grow watermelons! However, these plants will need to be started off in the protection and warmth of a glasshouse, polytunnel, or conservatory, and in the north of the country, (and in exposed positions) it may be preferable for watermelons to spend their entire lives indoors.
In the UK, I’ve found that the best time to sow watermelon seeds is from April to May (from mid to late spring). These seeds need warm temperatures of around 18-25C (65-77F) to trigger germination. Thankfully, you don’t need to provide your plants with as warm temperatures once your seedlings have germinated; young watermelon plants will grow quite happily in a light and bright environment that enjoys temperatures of 15C (59F) and above. However, don’t underestimate the importance of monitoring the temperatures inside your growing area, as watermelons are frost tender plants that will be killed by low temperatures. A reliable heater with a thermostat is essential to create and maintain the ideal growing conditions that these fruits require and ensure your plants’ survival on chilly nights. Watermelon plants will need to grow inside the warmth of a glasshouse or polytunnel (or inside a conservatory) until all risk of frost has passed, which can be anywhere from late May to the middle of June, depending on where you garden, in the UK.
If you don’t have a glasshouse, polytunnel, or conservatory, but you have a particularly bright and sunny, South facing window, you could try growing watermelon seeds on your window sill. Window sills don’t usually provide the optimum growing conditions found inside a glasshouse or polytunnel; as a result, if you’re planning to grow watermelons on your window sill, I’d advise you to sow your seeds in May.
I’ve found that watermelon plants thrive in containers of good quality, peat-free compost but for successful window sill growing you will need a sufficiently well lit space. Even new seedlings become leggy and weak within a couple of days – if the plants don’t enjoy sufficient light shinning down on them from above; as a result, you may need to supply your watermelon plants with additional LED lighting. If you have a warm conservatory, watermelons will grow happily in this protected environment.
In spring and summertime, bright sunlight shining through a window pane or glasshouse will often scorch plants, damaging their leaves; however, you can easily avoid leaf damage by protecting your plants from harsh sunlight using blinds or shade paint, which will soften the intensity of the sunlight that reaches your plants’ leaves.
Please don’t be too hasty when moving your watermelon plants outdoors – you need to be absolutely certain that all risk of frost has passed before moving these tender plants outdoors. Before moving your plants outside permanently, take care to thoroughly harden your watermelon plants off, by moving your plants outdoors in the morning and then bringing the plants back inside your glasshouse or conservatory again in the evening. This may seem like rather a lot of hassle, but this process will really help your plants; it’s best to spend a minimum of two weeks (and ideally four weeks) hardening your plants off, prior to planting.
Watermelons will be content to live their whole lives inside a warm glasshouse, polytunnel, or conservatory. In exposed areas, or in the North of the country, growing watermelons inside a glasshouse or polytunnel is often the best option to produce a good harvest. However, once all risk of frost has passed, watermelons can be grown outside in a bright and sunny, sheltered location. Plants can be grown in containers of good quality, peat-free compost, planted out in the soil at your allotment, or grown in garden borders or raised beds. It’s important to grow watermelons in moist but well-drained soils (avoid waterlogged soils at all costs) in very bright and sunny, sheltered locations.
Once your watermelon plants have produced five leaves, cut away the remainder of your plant’s stem after its fifth leaf. Then, when your plant has produced four side shoots, remove any new side shoots that form; this will concentrate all of your plant’s energy on watermelon production.
Watermelon plants can be grown as trailing plants along the ground or over a patio; alternatively, watermelons can be grown up a climbing structure or support frame. Plants that are grown over the ground will benefit from a tile being added under their fruits as they form – this will keep the developing melons off the wet ground where they are more prone to rotting and to attack from slugs and snails. It’s worth look out for slugs and snails and protecting your plants from them.
Articles that mention Watermelons:
- Apr. 2023 – Relax: Leave your Lawnmower in the Shed and Grow Fruit and Vegetables that Taste Incredible!
- Apr. 2021 – Productive, Decorative, & Sensationally Flavoured Edibles to Grow from Seed in April!
- Mar. 2021 – Watermelon ‘Little Darling’