Easy to grow and great to eat. Almost anyone with a bit of space can grow a watermelon. Full of nutrients such as citrulline, which helps the blood to circulate, these great tasting fruits are actually 92% water. So as well as being packed with nutrients, they also help to keep you hydrated.
Watermelon is a member of the Cucurbitaceae family alongside squash, cucumbers and pumpkins. These plants crave space, light, water and nutrients. If you can provide these things you can cultivate your own great tasting watermelon.
Sweet and juicy, this is a surprisingly straightforward fruit to grow.
Coming in a range of colors and shapes these are pleasingly attractive additions to the garden. Here is everything you need to know about growing your own watermelon crop.
Choosing the Right Variety For Your Climate
Choosing a variety that is suitable to your growing conditions makes successful cultivation a lot easier.
When selecting your plant, remember that watermelon requires an average daily temperature of 70 to 80 ℉. The more reliable the weather the better the plant grows.
If you only enjoy a short summer or are in a cold climate select a variety that is quick to mature. Plant towards the end of spring so that you can harvest the fruit in the summer.
Alternatively try planting undercover in a greenhouse. This is a great solution for growers in cooler climates or those who enjoy unreliable weather. Growing undercover enables you to create the ideal, artificial climate for your watermelon plants.
Gardeners in warmer climates can grow slower maturing varieties outdoors or undercover.
Should I Grow From Seed or Purchase a Young Plant?
As we have already noted, watermelon plants require a long growing season. Many varieties need at least 80 days.
Seeds are best sown in their final position. At the point of sowing the soil should be at least 70 ℉. The AcuRite Soil Thermometer is an easy to use way of accurately monitoring the temperature of your soil.
In cooler climates, or if you don’t enjoy a long summer try starting seeds undercover two to three weeks before you intend to plant out. Don’t sow seeds sooner than this. Large watermelon seedlings struggle to transplant successfully.
You can help the soil to warm up by covering it with a plastic sheet. Cover the soil at the same time as you sow the seeds.
As well as how quickly it takes the fruit to mature, when selecting your variety you also need to bear in mind the size of the plant. You don’t want to select a large plant that quickly outgrows its space and starts to smother other plants. .
Different varieties produce fruit in a range of shapes, sizes and colors. Be sure to select a variety that is able to develop fruit in your climate.
Golden Midget is a quick maturing variety, maturing in 70 days. The plant produces small, 3 pound yellow fruit with a pink flesh.
Sugar Baby takes about 80 days to mature and produces large 10 pound fruit with red flesh. Similarly the oblong fruiting Sweet Beauty also takes about 80 days to reach maturity. Filled with attractive red flesh, when mature the Sweet Beauty melon weighs about 6 pounds.
Congo produces large oblong fruit with green rinds and dark green stripes. The fruit weighs 30 to 40 pound when ripe.
Moon and Stars is one of the most attractive varieties. A heirloom variety, it is slow to mature, taking around 100 days. This plant produces dark green fruit with yellow spots Each fruit weighs around 25 pounds and is filled with sweet, red flesh.
Where to Purchase Your Seeds
Avoid using seeds from store purchased fruit. These are usually hybrids and are unlikely to produce good watermelon fruits. This is because hybrid fruits are often a special cross and rarely grow true to type.
Instead hybrids usually produce a fruit commonly known as pig melons. As the name suggests these are only good for pig food.
Don’t sow seeds harvested from store bought fruit. These rarely produce satisfying fruits.
Only purchase seed from reputable suppliers. Open pollinated heirloom varieties are preferable. The seeds from these fruits can be kept and sown the following year. Open pollinated varieties are also hardier than other cultivars.
Alternatively you can buy young plants from garden stores or nurseries.
Where to Grow
Watermelon plants struggle in extreme heat or humidity. While these are water loving plants they also struggle in overly wet or soggy conditions. Overly wet conditions can also attract bugs or fungal problems.
Watermelon plants like a deep, rich soil. The soil should also be light and well draining. It should also have a pH of between 5.5 to 7. A soil test kit quickly reveals your soil profile if you are unsure.
Amend heavier soils by working in lots of compost or organic matter before planting. This also helps to enrich your soil, giving the plants a further boost.
If you have poor soil you can grow in grow bags, raised beds, planters or containers filled with rich potting soil.
A raised bed filled with fresh, well draining potting soil is the ideal place to grow fruit and vegetables.
How to Sow Seeds
You can sow seeds outside 2 weeks after your last frost date as long as the soil is at least 70 ℉.
Use a shovel to work the bed over well before mounding the soil into heaps or ridges about 3 ft square and 1 ft high. Mounding is a particularly useful technique if you have heavy soil because it encourages water to drain away from the plant. Watermelon plants dislike sitting in waterlogged soil for prolonged periods.
If your soil is heavy or poor you can make the mounds out of compost instead.
Sow the seeds on the mounds as thinly as possible. Sow to a depth of about half an inch to 1 inch.
Sow twice as many seedlings as you want. Following germination remove the weaker seedlings, allowing healthy plants to grow on.
Water the soil well. A watering can provides an even spray that soaks the soil but isn’t so heavy that it disturbs or drowns the seed.
Keep the soil moist until germination occurs. Germination usually occurs within a few days.
Following germination, allow the seedlings to grow on, protecting them from pests such as slugs or snails. Thin out the seedlings to their recommended spacing when they are about 2 inches tall and have at least one set of true leaves.
The recommended spacing varies between varieties, this information can be found on the seed packet. In general plants should be spaced about 1 ft apart. Rows should be spaced out at 6 ft intervals. This gives the plants plenty of room to set out their vines and spread without becoming entangled.
Gardeners who enjoy long growing seasons can also try succession planting. This means instead of sowing all your seeds in one go, you sow small numbers of seeds at intervals of every few weeks. Succession planting allows you to enjoy a steady supply of fresh watermelon fruit.
Correctly spacing your plants helps air to circulate freely. This prevents fungal diseases from striking.
Sowing Seeds Undercover
Gardeners in cooler climates may need to start their seeds off undercover. While watermelon plants do best when sown into their final position, young seedlings can cope with transplanting.
To start seeds undercover, fill 4 inch pots with a good quality potting soil. Sow 3 seeds per pot.
Place the pots in a sunny position or under grow lights. The position should be warm, averaging around 80 ℉. Heat mats can also be used to encourage germination. The VIVOSUN Heating Pad is a durable product designed specifically for germination and seedling production.
Following germination, pick out the weakest seedlings allowing only the healthiest seedlings to grow on. After your last frost date has passed, harden off the seedlings before planting outside.
When you transplant the seedlings, handle them carefully. Try to disturb the fragile root system as little as possible.
Sowing in biodegradable or peat pots helps to avoid unnecessary root disturbance, making transplanting easier. When you are ready to transplant simply dig a hole large enough to hold the pot. Trim away the rim of the pot so that it sits level with the soil and place in the hole.
Backfill any space around the pot and water well. Continue to water well for several days to help prevent transplant shock. Remember to protect young plants from pests.
Aim to transplant your seedlings as soon after germination as possible. The longer you allow plants to grow on before transplanting the less likely they are to succeed.
Companion planting is the practice of growing mutually beneficial plants alongside each other. In the case of watermelon cultivation there are certain plants you can grow alongside your watermelon plants to prevent aphids and cucumber beetles from attacking the plants.
The following plants either deter melon aphids or act as trap plants, preventing watermelon plants from coming under attack:
The following plants deter cucumber beetle:
Bright and attractive, Nasturtiums are one of the most useful companion plants.
Plants to Avoid
Avoid planting lots of members of the Cucurbitaceae family together. As well as watermelon these include cucumber, pumpkin, squash and zucchini. These plants are all vulnerable to the same pests, including the destructive cucumber beetle. Should cucumber beetles strike, spacing out your plants helps to prevent the pest from easily decimating a crop.
You should also avoid planting near asters, potatoes, roses and sunflowers because they all attract aphids.
Finally, avoid planting in the same bed as peppers and tomatoes. These are all large, leafy plants and planting all three together can cause overcrowding. Air can struggle to circulate in a densely packed bed. Poor air circulation can help fungal diseases to thrive.
How to Care for Watermelon Plants
Protect plants from slugs and snails in particular. Mulching can help to deter pests.
Mulching also helps to deter weed growth. Weeding can disturb the plant’s shallow root system, so mulching is preferable.
Remember to protect young plants and fruits from pests. They should also have enough room to spread and develop freely.
How Often Should I Water my Plants?
Watermelon plants have a shallow root system. This means that they require lots of moisture. Keep the soil evenly moist, never let it dry out. During dry spells the plants can require up to 2 inches of water a week.
When to Fertilize
A healthy growing plant requires lots of fertilizer. Like other cucurbits they like raw compost and manure. You can also apply reliable homemade or organic fertilizers such as chicken manure pellets.
Feeds rich in nitrogen can be applied when the plant is growing. Once flowers start to form, reduce nitrogen rich feeds and instead apply fertilizers rich in potassium. African Violet fertilizer or liquid seaweed is ideal. Alternatively, an application of slow release fertilizer provides a steady supply of nutrients throughout the growing season.
How to Prune Your Plants
Pinch out vines once they reach about 6 ft in length. This encourages branching. Pinching out can also be done to prevent plants from outgrowing their area and encroaching on other crops.
Usually the first flowers on each branch produce the best fruit. Once several fruits have set and are starting to swell some growers pinch out the tip of the branch. This prevents other flowers and fruit from forming. Pinching out the branch tip also encourages the set fruit to grow as large as possible.
In colder areas cut away flowers that form within 50 days of your first predicted frost date. These flowers won’t have time to develop into fruit before the frosts arrive. Cutting them away encourages the plant to put its energies into the fruit already forming on the plant.
Flowering and Fruiting
Watermelon plants produce male and female flowers on the same vine. Smaller male flowers appear first. These are followed by larger female blooms.
Sometimes female flowers can fail to appear. This can be because it is too cold or too hot. It can also be a sign that the plant is not receiving enough water or nutrients.
The fruit forms at the base of the female flower. If this fails to grow or becomes shrivelled it means that the flower hasn’t been pollinated.
Plants growing outdoors are naturally pollinated by visiting pollinators. If these fail to visit, or if you are growing undercover, you may need to hand pollinate your plants.
Hand pollination is best done early in the morning.
To hand pollinate, remove several male flowers and pick away their petals. Brush the pollen laden stamen of the male flower against the stigma of the female flower. The stigma is loathed in the center of the flower. As you brush the stamen against the stigma, pollen sticks to the stigma.
Remember to Raise the Fruit off the Ground
As the fruit develops, gently lift it onto an organic mat or straw. This helps to prevent fruit from sitting on wet ground where it can rot.
As the fruit develops it sits on the ground. Placing the fruit on a mat or elevating it prevents it from rotting.
You can also train the vines to grow along a trellis. This lifts the fruit above the ground, preventing it from rotting in wet conditions. It also frees up more soil in your beds, allowing you to plant more crops or flowers.
Make sure that your vines are firmly attached and that the trellis is secure. As the fruit develops the plant becomes heavier. A poorly secured trellis can snap or fall under the weight of a heavy plant.
Finally remember to support the elevated fruit in Melon Hammocks. Burlap or fabric shopping bags can also be used to support the growing fruit.
When Can I Harvest my Watermelon?
The easiest way to tell if your fruit is ripe is to rap it with your knuckles. If, when you knock the fruit, you hear a dull, hollow sound the fruit is ripe. Unripe fruit makes a higher pitched, fuller noise when knocked.
The skin of the fruit also changes as it ripens. Most of the skin darkens in color and becomes tougher. Meanwhile the light colored patch on the bottom of the fruit turns from green to yellow as the fruit ripens.
A final way to tell if your fruit is tipe is to watch the curly tendril at the stem. Once this is totally dry your melon is probably ready.
Once ripe cut the fruit away from the plant and enjoy.
Ripe fruit sounds hollow when knocked. The skin also darkens and becomes tougher as it matures.
Common Watermelon Problems and How to Prevent Them
If planted and cared for correctly, the plants are pleasingly disease free.
Correctly spacing out your plants, so that air can circulate freely between the vines, is the easiest way to prevent mildew and fungal issues. Fungal problems also thrive in humid conditions. Watering the soil, keeping the leaves as dry as possible helps to keep humidity levels low.
Leaf eating beetles, such as striped cucumber beetles or pumpkin beetles can also target plants. Regularly check the fruit and foliage for signs of infestation.
Pest infestations can be a sign that the plants are unhappy or stressed. Planting in good soil, and caring correctly enables your plants to withstand a few pests. A large infestation is more problematic. Homemade insecticidal soap cures most infestations, but to fully cure the problem you may also need to address any underlying causes.
Aphids can also target watermelon plants. Infestations can be washed from the foliage with a blast from a hose.
If you plan on growing watermelon crops alongside other fruits and vegetables every year try implementing a basic crop rotation system. This helps to keep your soil healthy and disease free.
Sweet and juicy the watermelon is a popular addition to the garden.
Sweet and juicy watermelon plants have been grown for over 5000 years. Originating in Africa, today the plants are a common fruit grown all over the world. With the right variety and regular care, anybody, regardless of their location, can grow and enjoy the great taste of fresh watermelon.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.