Find out everything you need to know on how to grow watermelons from planting, caring, and harvesting watermelon from your home garden.
Watermelon is the perfect summer snack and summer gardening project! Starting right as your temperatures start to increase in the spring, you can have fresh watermelons for all your picnicking needs in less than 3 months.
Whether you’re looking for large and juicy or small and manageable, there are a variety of watermelon types that can grow in many different climate zones. Any gardener can introduce watermelons to their collection so here’s everything you need to know about growing amazing watermelons this season.
Watermelon’s botanical name is Citrullus lanatus and depending on your climate and space to work with, there are over a hundred different watermelon varieties to choose from. As a home gardener, you don’t have to be confined to your standard large red watermelon. You can choose between seedless and seeded, icebox or picnic types, and red, orange, or yellow varieties.
You’ll need to take into account if they’re short vine or long vine to account for space though generally watermelons are known to be a sprawling vine plant. Some watermelon varieties will be more durable than others, able to withstand lower temperatures, less fertile soil, and less light.
Here are a few common names you’ll find when choosing the right watermelon for your garden:
- Icebox Watermelon: Blacktail Mountain, Tiger Baby, Sugar Baby, Sweet Beauty
- Seedless Watermelon: Crimson, Bijou, King of Hearts, Millionaire, Nova
- Picnic Watermelons: Crimson Sweet, Jubilee, Allsweet, Sweet Princess
- Yellow and Orange Watermelons: Yellow Doll, Honeyheart, Tendergold, Desert King
Ideal Growing Conditions for Growing Watermelon
Best Climate for Growing Watermelons
Watermelons grow in warm climates with temperatures above 71°F (22°C). You’ll need to wait for the last frost to completely thaw before planting watermelon seeds in the ground.
So wait at least 2 weeks after any frost before planting outdoors. And because of the long growing season required of around 3 months, in some areas, you’ll need to start the germination period inside.
Watermelon cannot survive cold temperatures which can reduce the flavor of the fruit and cause the plant to fail altogether. Some gardeners put down black mulch or plastic on the soil to help it warm up and keep it warm.
Soil for Watermelons
Growing best on mounded soil hills, watermelons love loamy fertile soil that’s free-draining. The ideal pH balance for the soil is pH 6 to 6.8 though they will tolerate down to pH 5. Compost and aged manure can be added to the soil prior to planting to help increase soil fertility and assist with soil drainage.
Sun Requirements for Watermelons
Watermelons need long, sunny days in full sun. So choose the sunniest spot in your garden to plant your watermelons. Plan on 8-10 hours of sun a day for watermelon to really thrive.
The soil should remain moist while the watermelons are growing, though be careful not to waterlog the area. Some gardeners recommend about 1 to 2 inches per week, but it will depend on how well your soil stays watered.
Water the soil directly rather than overhead watering so as to avoid getting the leaves wet. Drip irrigation or a soaker makes this job easier.
When the watermelon is about a week away from maturity and planned harvest, you can reduce the amount of watering, for a sweeter melon result.
Adding mulch to your watermelon’s growth area will help the soil retain moisture, reduce weed growth, and keep the fruit off the ground. Straw or even cardboard can be good options.
Starting with good soil is important for thriving watermelon plants. Throughout the growing season, a slow-release fertilizer will support the plant’s growth. Look for an organic fertilizer like this one. And if you have access to compost and aged manure, these can be used also. Topdressing the plants with compost and manure a few times throughout the growing season will keep your plants very happy.
Planting Your Watermelons
Starting Watermelon Seed Indoors
You can start your watermelon seedlings inside, as long as the outside temperature is expected to heat up to consistently above 71°F degrees (22°C) within a month. By planting seeds into biodegradable peat pots, you can later plant the seedlings into the ground without disturbing the fragile root system.
If you start watermelon seed indoors, consider using a heat mat to warm up the soil and assist your germination success.
Seeds can be planted about 1/2 inch deep into an organic seed-raising mix. Water in well and then water lightly on a daily basis to keep the soil moist but not soggy.
Place the seeds near a sunny window or use a grow lamp to provide adequate light.
Once your watermelon seedlings are around 4 weeks old, and the temperature has warmed up, they can be transplanted outdoors.
Seedlings should be ‘hardened off’ before being moved outdoors. This is the process of gradually exposing the seedlings to outdoor conditions. You can read more in our article How To Harden Off Seedlings here.
Planting Watermelon Seed Directly in the Ground
Watermelon seeds can be planted 1/2 inch into the ground. Watermelons do need a lot of room to sprawl and spread out. In fact, some long vine strands can reach up to 20 feet (6 meters) in length. But smaller varieties will take up a lot less space. So make sure you check the seed packet and choose a variety of watermelon that will work well with your available space.
If you have a large area and you plan to grow numerous watermelon plants, plan four feet (1.2 meters) between each watermelon seed in a row. The rows should be about six feet (1.8 meters) apart.
For smaller watermelons, like icebox or miniature varieties, you can plant them about 3 feet (90cm) between each row.
When mapping out an area for your garden, have a general 2-feet-by-3-feet (60-90cm) range for each small watermelon seed. Large watermelon seeds should have about a 4-feet-by-6-feet (1.2-1.8 meter) area.
You’ll want to make an 8 to 12-inch (20-30cm) soil mound from fertile, free-draining soil where you’ll be able to plant the seed or new seedling. The soil mounds are primarily used as a way for water to help drain away from the plant roots. So it should be noted here that if you live in a very dry climate, you might actually do the opposite by planting into shallow holes instead.
Sow seeds about 1/2 inch deep with 2-4 seeds in each planting hole.
Water seeds and seedlings well and make sure they are watered regularly while they establish. Often daily watering is required.
In 7-10 days, you should see the seed germinate. Once they have 2-3 sets of true leaves you can thin out the seedlings to give the strongest plants enough room to grow. You can leave the biggest 2 plants to continue growing and cut the others at the base, or very carefully transplant them to another area of the garden.
If Space is Limited
As we’ve seen, watermelon loves a lot of room to grow. Ideally, they will have their own patch of the garden to sprawl and spread as they like. But if space is limited you can plan to plant your watermelon at the edge of the garden, so they don’t take over every else.
Watermelon can also be grown vertically on a trellis. You will need to provide a really strong trellis to support the weight of the watermelon fruit and the fruit themselves will need to be supported as they grow so as not to snap off the vine. Pantyhose have been used to make a sling to hold the watermelon fruit.
Smaller, male flowers will appear first and then the female fruit-bearing flowers will follow. Having bees and other beneficial insects in your garden will pollinate the watermelon fruit, with honeybees being one of the best pollinators for watermelon.
You can also assist pollination by hand pollinating the flowers yourself. This may be necessary if you have a lack of beneficial insects to do the job for you.
Do this by using a small clean paintbrush and gently brushing inside the male flower before brushing inside the female flower. This just transfers the pollen from one flower to the other, leading to successful pollination
Another option is the remove a male flower from the stem, peel back the petals to revel the stamen and use it to directly brush inside the female flower.
Once the watermelon fruits form, it’s a good idea to place straw under the fruit to protect it from laying directly on the soil. Some gardeners use cardboard just as effectively.
How Long Does it Take to Grow Watermelons?
For smaller watermelon varieties like icebox watermelons, the growth time can be from 80 to 90 days. Main season watermelons are more likely to take 100 to 120 days.
How Much Does A Watermelon Weigh?
A watermelon can weigh anywhere from 10 to 40 pounds (4.5-18kg) with the average being 20 pounds (9kg).
You might be interested to know that the world’s biggest watermelon weighed in at 350.5 pounds (159kg)! But don’t worry, unless you’re going for the world record, you’ll most like end up with an average-sized watermelon.
When are Watermelons Ready to Harvest?
You may already be familiar with the “thumping method”, whereby you tap the watermelon to listen for a hollow sound that indicates ripeness. You can compare this to an unripe watermelon which will help train your ear for the difference in sound. There are other clues to also help you determine when your watermelon is ready to harvest.
The watermelon stem and nearby vines are typically going to look brown and almost brittle and the watermelon fruit will practically snap right off the vine.
The bottom side, or “ground spot”, of the fruit will go from almost white to a creamy yellow color.
When a watermelon is ripe and ready to harvest, the surface will look a little rough and dull, having less of a sheen and differentiation between the strips.
It’s important to reduce how much you water the plants when they’re about to be harvested. This is in order to keep it tasting fresh and sweet. So about a week out from harvest, reduce watering but don’t eliminate it entirely.
Watermelons can be stored uncut for two-three weeks or a slightly longer time in a cool place like a basement.
Once they’ve been cut, watermelons can be stored in the refrigerator for about four days. You can wrap them tightly in plastic wrap or use some beeswax wrapping paper. It’s better to eat the watermelon sooner rather than later, though, as they’re going to be sweeter.
Watermelons don’t ripen after you’ve removed them from the vine, so you don’t need to wait a few days after harvest to cut into one.
Watermelon can also be frozen by cutting off the skin and freezing in pieces. Frozen watermelon is delicious as a watermelon slushie!
The rind of the watermelon is also edible once pickled. And having tried pickled watermelon, I can tell you it is surprisingly delicious.
And if you’re looking for ways to use your watermelon, you might like to see our Easy Watermelon Salad Recipe with Feta, Mint, Balsamic.
Pests and Disease
Common Pests and Treatment
Although watermelons prefer warmer and humid climates, this tends to also be the weather that promotes disease and attracts pests. Watermelon fruit can attract aphids, mites, and certain beetles. You can tell when you have a problem if you see bites in the leaves or if there are trails across the stems and fruit.
Aphids can vary in color, from a light green or tan to a darker purple or green. They’re pear-shaped, soft-bodied insects that are about 1 to 2 mm in length. Adults may or may not have wings, depending on their variants. They can typically be easy to spot since they group on the vines and leaves of the fruit and are followed by ants, which like to feed off of their honeydew.
Mites can kill or stunt the growth of your crops because they feed on the cells of the plant. You’ll notice they’ve been feeding if you see yellow or rusty spots on the leaves. Because they’re so small, less than 1 mm in length, they’re difficult to detect until there’s already a feeding problem. You’ll want to take precautionary measures to combat these pests.
Mix a small amount of liquid washing up soap into a spray bottle filled with warm water, spray the underside of the fruit’s leaves and any nearby leafy surfaces. This specifically targets aphids, dehydrating them as they congregate, but will make it difficult for other pests to feed off of the leaves as well. Garlic and hot pepper sprays will also help deter pests but will only keep for about a week in your refrigerator. Horticultural neem oil is also beneficial to eliminate pests.
Common Diseases and Treatment
Common diseases to look out for in your watermelon patch are anthracnose, gummy stem blight, and bacterial fruit blotch.
Anthracnose is a fungus that develops from cold, rainy weather that lasts a few days. Yellowish, water-soaked spots will appear on leaves and will eventually grow larger and turn black. The fruit can develop dark, wet cankers of various sizes.
Gummy stem blight affects the leaves and stem and can lead to black fruit rot. Brown or tan spots appear on the leaves and can eventually cover the entire leaf with a brown, sticky substance. The stem can split from cankers and if there’s already fruit growing, the rind can develop a wet rot.
Some of these diseases will be weather-related while others can start within the seeds. Be sure you’re purchasing your seeds or seedlings from a reputable source and monitor the fruit’s condition after weather changes. Take preventative measures to ensure the leaves and vines have a healthy growth period and maintain a regular check-up on budding fruit to quickly remove any affected vines or buds.
In order to keep your watermelon patch safer and less inviting for pests, there are a few natural solutions:
- Regularly remove any weeds from the area: these will attract pests and can infest root systems.
- Plant seeds in a well-drained area: moisture and over-watering can lead to the development of various fungi.
- Choose quality mulch and fertilizer that repels pests: you can source local manure from trusted farms or compost from your own food and garden waste.
- Regularly rotate crops: Many pests and diseases can survive throughout winter and will reestablish their presence if you don’t rotate and clear plots.
- Invest in horticultural need oil.
Enjoy a Summer of Watermelons
Now that you know all about the ideal growing conditions for watermelons, it’s time to get growing so you too can enjoy a summer filled with delicious tasting watermelons. And once you’ve tasted your own homegrown watermelons you’ll never want to go back to store bought. So which variety of watermelon will you grow this season?
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