Sweet and watery watermelons are without a doubt an iconic summer fruit due of their high water content and soft red flesh. Those supermarket melons can’t be like homegrown fresh and organic melons. You can even plant them in a small space like a balcony, it is possible by growing watermelon vertically in a pot.
Watermelon has long taproot and it doesn’t transplant well that’s why it is better to sow the seeds directly in a pot. Sow 3-4 seeds directly in a pot once the temperature starts to reach 65 F (19 C) and above in the spring. In tropics (USDA Zone 10-11), the best time to sow seeds is winter and early spring. The germination takes place within 6 to 10 days. Thin out and leave only one of the strongest seedlings per pot.
Choosing a Pot
Growing watermelon in containers is not much difficult though tricky. You need to understand the basics. As watermelon has long taproot choosing a deep pot is essential. A large pot or bucket that is at least 2 feet deep and half wide is required.
To know everything about watermelon varieties, see this excellent guide at Washington State University site.
Watermelon: Quick Care Guide
A watermelon surrounded by its vine. Source: Lorianne DiSabato
|Common Name||Watermelon (plus a bunch of individual variety names)|
|Scientific Name||Citrullus lanatus|
|Germination Time||14 days|
|Days to Harvest||70-100 depending on variety|
|Water||1” per week in mild weather, 2” in hot|
|Temperature||70-90 degrees during the day optimal|
|Humidity||Tolerates humidity but may develop mildew|
|Soil||Loamy, well-draining soil w/lots of compost|
|Fertilizer||High N for plant growth, then switch to high P-K for blooming/fruit set|
|Pests||Cucumber beetles, squash bugs, squash vine borers, aphids, spider mites|
|Diseases||Fusarium (especially wilts), anthracnose, downy mildew, powdery mildew, alternaria, curly top|
Requirements for Growing Watermelon in Containers
Watermelons should be grown in a sunny position. If you’re growing it on a balcony or on a roof garden where space is tight, growing watermelon vertically on a trellis is a solution. Trellis should be minimum 4 feet tall and sturdy enough to carry the weight of melons.
Watermelons are warm weather annuals but they can be planted in both tropical and temperate regions easily. It is possible to grow watermelons in temperature around 50-95 F (10-35 C). The optimum growing temperature is around 65-85 F (18-30 C).
Sandy and loamy soil is suitable for growing watermelons. Ideal soil pH is around 6 – 6.8. Avoid compact, clayey soils. Airy and well-drained substrate promotes the growth of the plant. Also, application of the well-rotted horse, rabbit or cow manure improves the texture of soil and provides nutrients constantly.
Watermelon requires a lot of water. Keep the soil evenly moist but not wet, the water must drain freely from the bottom. When growing watermelon in containers, you’ll need to water the plant every day and sometimes twice in a warm day. Once the fruits start to swell up and mature, reduce the watering. In that period, water carefully and moderately. Avoid overwatering and underwatering both to get the sweetest melons.
Watermelon Plant Care
Start to fertilize the plant with a complete liquid fertilizer. Once, the plant starts to flower and appear to set fruits, use a fertilizer with less nitrogen. Consider liquid seaweed fertilizer.
To get a healthy and more productive plant, only allow the main vine to grow. When the plant is young, remove side branches before they grow more. Also, remove those stems that are damaged and diseased.
Watermelon vine produces both male and female flowers separately. However, pollinators (bees and butterflies) will pollinate them but to be sure you’ll need to hand-pollinate the flowers to make sure you get fruits. The first ripe fruits appear after approx. 40 days after pollination of flowers.
Diseases and Pests
Usually, you can easily care and look after the watermelon growing in a pot. Still, it is little prone to diseases when exposed to too hot-humid or too cold weather, or due to waterlogged soil. Common garden pests like aphids, cucumber beetles and those that affect the squashes and cucumbers can infect it.
Watermelon plants on a balcony
The harvesting period depends on the climate, season, and variety. Generally, it usually begins 80-90 days later after seed sowing and between 30 to 50 days after flowering. Flowering and fruit setting continue for several weeks until the weather remains favorable and you’ll get several harvests.
Ripe fruit does not seem special. Smell and no change in color of the skin occurs. To see if the fruit is ripe, you should knock with fingers on the surface of the watermelon. If you hear a dead, hollow sound, this means that the fruit is already ripe. Another method is to check the tendril if it is fading and half dead then your watermelon is almost ripe. If it is faded, the fruit is ripe or overripe.
- In cool short summer climates, start the seeds indoors or in a greenhouse either directly in a container or in a biodegradable pot.
- Use a lot of organic matter for growing watermelons in containers as they are heavy feeders. Side dress your potted melon plant with manure or compost in every 3-4 weeks. Scrap and remove topsoil if there is no space in the container.
- Stress (change in temperature, pests or diseases, overwatering or lack of water) to the plant at the time when fruits are maturing, results in less flavorsome and sweet fruits.
- In a small space, growing melons vertically on a trellis is a great way to save space. Use netting, a bag or a stretchable cloth to create a hammock under the fruit to support it.
- The trick for getting best quality fruits is to don’t let the plant set so many fruits. 2-3 fruits at the same time for large fruit varieties and 4-5 fruits for the smaller one is sufficient.
- Do successive planting for regular harvests. Plant 2-4 plants and do the same after 2 weeks.
Ideal temperature to grow
The temperature should be quite sunny. If you are growing them on a balcony or on a roof garden where there is a lack of light then make use of a trellis. Ensure that trellis should be minimum 4 feet in height and strong enough to carry the weight of melons. The optimal temperature is 18-30 C and can also be grown at the temperature of about 10-35 C.
Usually, it begins after 80-90 days of seed sowing and between 30 – 50 days after flowering. It depends on the climate, season and you will see several harvests depending on the climatic conditions.
If you want to check whether the fruit is ripe or not then you need to do it manually as the ripe fruit doesn’t look special with merely no change in color and smell. One way is to knock on its surface. If you hear a dead or hollow sound then it is a sign that fruit is ripe and if the trendil looks fully faded then it is overripe.
Few useful tips-
- Watermelon plants are a heavy feeder and so use a lot of organic matter in fertilizer. Composting is required in every 3 – 4 weeks. Remove the topsoil if you find a lack of space in the container.
- Do not allow the plant to set more than 2 -3 fruits at the same time to get the best quality yield. Successful planting and a regular harvesting say 2 – 4 plants after every 2 weeks would do.
- Take care of the temperature in which the plant is being grown. An exposure to extreme climatic conditions (warm and cold) at the stage of maturity can result in less sweet fruits.
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Sowing and planting watermelon
Watermelon needs a lot of heat to germinate well, because the seedlings can’t cope in the least with frost.
Since it needs warmth, it is best to grow it in regions nearer the Equator, or at least in a greenhouse if you’re far from it.
Seedlings can be prepared indoors in nursery pots, in a warm and well-lit room. The ideal temperature range is between 72°F and 75°F (22°C to 24°C).
The right season to sow watermelon
Depending on the climate in your area, sowing watermelon is best starting from the month of March under cover in nursery pots followed by transplanting in May after any risk of freezing has disappeared, or you can also wait for May and proceed to sow directly in the plot.
- Watermelon fears the cold, and requires warm to hot climate to germinate properly.
- Watermelon loves rather rich soil, feel free to amend the soil with compost or fertilizer before planting.
If sowing in nursery pots, count more or less 3 weeks before transplanting them to the ground. That’s why there is no need to sow early.
- Lightly press 2 to 3 seeds down in each nursery pot.
- Ensure that temperature doesn’t drop below 50°F (12°C) during germination.
- Once sprouted, keep only the most vigorous seedling.
- 3 weeks later, they can be set into their growing bed, provided that the last frost spells are past already.
- Provide for at least 3 feet (1 meter) between each plant.
Sowing watermelon seeds directly in the ground
It is also possible to sow directly in the ground starting from the month of May, if the area is prone to mild fall seasons.
This is the case in coastal areas such as climates nearer the Equator.
- Watermelon requires rich soil to produce a nice harvest.
- Feel free to add fertilizer or compost upon planting.
- Loosen up the soil well before before sowing watermelon.
- Provide for at least 3 feet (1 meter) between each plant.
Pruning and caring for watermelon
Since watermelon requires a lot of heat, it is recommended to place dark stones, shingles or tiles around the foot of the plant, they’ll store heat and share it to the plant.
Trimming the watermelon
If you’ve got the space in your garden or vegetable patch, you don’t need to trim or prune your watermelon to get nice watermelons.
Only prune for maintenance if you’ve got to control its spread to keep it from turning invasive and running over other growth.
- If so, pinch the watermelon stem just after a female flower (light yellow), counting a few leaves after the flower and cutting there.
Watermelon needs a lot of water to develop well and grow fat, especially in case of heat and/or extended dry spell.
- Water in the morning without wetting the leaves over the summer.
- Stop watering entirely 1 week before harvesting, because otherwise the watermelons would risk bursting open prematurely.
**Watermelons do not further ripen when they are off the vine. This makes harvesting season a bit tricky.
**There are many theories to consider when you are trying to figure out if your watermelon is ripe and ready to eat:
- When your watermelon flowers are in full bloom, they will be ripe for eating in 5 weeks.
- Where the stem of the watermelon meets the main vine, there is often a curling tendril. If this tendril is brown/dry, your melon is probably ripe. If the tendril is green, the watermelon is probably still growing.
- Look at the underside of the watermelon: if it’s white instead of yellow, your watermelon probably isn’t ripe yet (this can depend on the variety, however).
- Gently knock on your watermelon (I usually flick it instead): if it has a deep, hollow sound, it is probably ripe (the sound is hard to describe, but trial and error will help you figure out the best sound).
**When your watermelon is ripe, snip them from the vine with gardening shears.
**Store uncut watermelon at room temperature to keep them super tasty. ONLY put them in the fridge when they have been cut open!
**Saving seeds for future crops works best with heirloom watermelon seeds:
- Scoop out the seeds and place in a wire mesh sieve. Pour running water over them and gently rub away the stringy fibers.
- Place cleaned seeds in a bowl of water and stir a few times. Throw away the floating seeds: they are sterile/immature/etc. Stir a few more times and repeat the process of throwing away the floating seeds.
- Drain the remaining seeds. Line a cookie sheet with waxed paper, spread the seeds in a single layer on the waxed paper and place in a sunny spot outdoors to air-dry.
- Occasionally stir the seeds a bit to make sure all of the sides are exposed to air and sunlight for even drying.
- At the end of the day, bring the seeds indoors and continue to dry them for 1-2 weeks. Stir daily for even drying.
- Since watermelons have such thick seeds, you need to make sure they are thoroughly dry before storing them: humidity, rain, etc. can add on a few more weeks of drying.
- Store them in a dry, dark place until next summer.
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