Who doesn’t love a juicy watermelon?
I do and that’s why I made this complete guide on growing watermelon indoors.
It is possible to grow watermelons using a pot in an apartment or if you have a conservatory you could easily grow a bumper crop in a container.
It’s not easy and maybe not for a total beginner to indoor gardening but it is possible and the results are incredibly satisfying.
If you follow this information you will be able to grow a watermelon in your house or apartment in the middle of a city.
Give it a try what have you got to lose? Read on and you will learn how to grow a watermelon indoors…
To grow a watermelon plant indoors simply use seeds from a store bought watermelon. Plant them in a 5-gallon container with general potting soil. Use a trellis system so your plant grows up the way. If they get less than 8 hours of sunlight using an LED grow lamp on a timer to top up the light.
What variety of watermelon is best for growing indoors?
When you are growing watermelon indoors it is a good idea to pick a variety that is suited to your local climate and with a short growing season.
Look for a compact variety that produces small fruit.
Some varieties ideal for indoor growing includes Jubilee watermelon, Golden Midget, Solitaire, Orange Sweet, Millennium watermelon, Jade Star, Moon and Stars watermelon, Sugar Baby watermelon, Crimson Sweet watermelon, and Early Moonbeam.
Be sure to do your research and pick a variety suited to your local climate.
This video shows the results of a watermelon grown indoors:
Should I grow a watermelon from seed or buy a young plant?
There are two options for starting watermelon plants.
The first is to plant a seed you have collected from a watermelon or but one from a seed store.
The second is to buy a watermelon transplant from a nursery. If you buy a transplant you have peace of mind that it will grow (if looked after properly).
If you use seeds there is no guarantee they will germinate and start to grow, for this reason, you should always start to grow more than you require then only keep the healthiest specimens.
How to germinate watermelon seeds
To prepare your watermelon seeds for indoor germination remove your seeds and give them a rinse to remove any remaining fruit and leave them to dry.
Fertilize the pot or container before planting the seeds to encourage quick germination. Push your seeds into the soil but not too deep, only push them between half an inch and an inch deep into the soil.
Keep your planted seeds somewhere warm until the shoots begin to show.
If you keep your watermelon seeds at 90 degrees Fahrenheit it will take approximately 3 days for germination to occur and if you keep your seeds at 70 degrees Fahrenheit it will take approximately 10 days.
Not all seeds will germinate so you should attempt to germinate more than you require then only keep the ones that are doing best.
What sort of container should I use for an indoor watermelon plant?
A big pot or container with drainage holes in the bottom are required to grow a healthy watermelon plant that will thrive and produce the delicious watermelon fruits that you crave.
I would recommend that you use at least a 5-gallon container, the bigger the better and at least 2 feet deep.
You will definitely need a container that you can fit some sort of trellis system, that is a system that you train your watermelon plant to grow up the way. Check out my article on the best trellis systems for indoor plants.
How to make a trellis system for watermelons
When growing watermelon indoors you will need them to grow up the way and not out the way. To do this you will need a trellis system and it is quite simple to make one.
You could make a grid out of bamboo sticks with the holes being about 6 inches wide and put it in your container.
Another option is to use 2 bamboo sticks and use a plastic net-like tomato netting with the holes about 6 inches wide.
The idea is you want to make it like a wall with holes in it so when your plant starts to grow you can wrap it through the holes and train it to grow up the way.
When watermelons start to grow you will need to attach some sort of support under them to stop them falling off due to the weight.
You can do this by attaching something like cloth or a piece of netting to your trellis and this will enable you to grow big juicy watermelons that grow up the way.
What sort of soil should I use for a watermelon plant?
The best soil to use when planting your watermelon is a general potting soil, ideally one with some peat soil mixed in.
If you are feeling brave and don’t mind your place stinking you could add in some cow manure that will constantly release nutrients as your plant grows.
Definitely, don’t use soil from your garden as it will become compact which is not ideal for growing fruit in pots.
How much light does a watermelon plant require?
Watermelons require around 8 – 10 hours of direct sunlight every day.
The most important thing the sun does is heats up the soil, so indoor plants can thrive with slightly less direct sunlight if they are kept warm.
If you don’t have a south-facing window or a conservatory you can always buy an indoor grow light and put it on a 10-hour timer (that’s what I do).
Make sure your timer is set to be off when it’s dark as watermelon plants need beauty sleep to make big beautiful melons!
How often should I water my watermelon plant?
Watermelons are big juicy fruits so they do require quite a lot of water to grow big, juicy, tasty and healthy.
They have deep roots so you will need to give them a good watering to keep the soil moist, water them until water starts to run out the drainage holes in the bottom of your container.
During the growing season, you should water your watermelon container every day and even twice a day if the weather is very hot.
Monitor the dampness of the soil your plant it is and use your judgment to set a watering routine.
Once your watermelons are nearing full size you should reduce the watering to around half the amount you have been giving them.
What temperature is best for indoor melon plants?
Watermelons are tropical plants so they do love hot weather.
The ideal temperature for growing watermelons indoors is between 65 degrees Fahrenheit and 85 degrees Fahrenheit (18-30 C).
If you love watermelons and don’t have that sort of temperature don’t worry because it is possible to grow them in temperatures between 50F and 95F (10 – 35 degrees Celsius).
So watermelons are actually incredibly versatile and grow in most climates. Just make sure they never see any frost or you may kill them!
What is the best fertilizer for a watermelon plant in a pot?
I always use a complete liquid fertilizer when I start growing a watermelon plant or even before I start I give the soil a dose of fertilizer.
Once the fruits start to appear I switch to a seaweed fertilizer as it has less nitrogen and the fruits prefer this type of fertilizer.
You should use fertilizer on your plants once per week during the growing season.
Should I prune an indoor watermelon plant in a pot
Yes, you should prune your indoor watermelon plant as it helps to control the size of your plant, helps promote healthy vines and increases the size of the remaining fruit.
When your plant is young you should remove any side branches that grow to encourage the main vine to grow big and healthy, it can grow up to 3 feet long.
You should also quickly remove any rotten, diseased or dead branches or fruits that appear during the season.
How to pollinate a watermelon plant?
As you need bees to pollinate watermelon plants you will need to do the job yourself by hand if you are growing yours indoors.
The flowers may only open up and be suitable for pollination for a day or two, so you do have to act swiftly to pollinate them and get fruits.
Find a male flower, these will be the flowers that have a long stem called a stamen coming out the center and use a small soft brush to brush pollen off that can be used for pollination.
Find a female flower, these have a small sticky knob called a stigma in the center of them that is designed so that pollen sticks to it.
Now go round the plant and brush the pollen from the male flowers into the sticky part of the female plants. The more you do this the more watermelons your plants should produce.
Should I thin out any heavy clusters of watermelons?
Yes, when lots of fruits start to appear on your watermelon vine don’t immediately go on a rampage and start cutting them off.
Leave the fruits to see how they start to develop and the least healthy ones will begin to shrivel and fall off naturally.
If you want standard sized watermelons you should only have 3 or 4 remaining, if you have more than that then cut some off only keeping the 3 or 4 healthiest ones.
If your dream is to produce a big show winning specimen then you will need to cut off watermelons ensuring you only keep the biggest healthiest specimen.
The general rule is, the more watermelons you have on your vine the smaller they will grow.
When to pick watermelons
Watermelons don’t get sweeter once you have harvested them so it’s important to only pick them when they are ripe or else you will have sour fruits and you don’t want that.
To tell if your watermelon is ripe check the tendril, this is a little shoot that is close to where the stem is attached to the melon.
If the tendril is green it’s not ripe, if it’s brown and dead your watermelon is ripe.
Check the bottom of your watermelon and if its white then your watermelon is not ripe if its cream or yellow then your fruit is ripe.
Failing everything else give your watermelon a good whack and if it sounds hollow then it is ripe. Ripe watermelons should easily twist off the vine so if you find it difficult then your fruit is not ripe yet.
How to store fresh watermelons
Although watermelons do look hardy they are actually quite perishable and should be stored correctly to extend the life of them.
To store your uncut watermelons don’t just leave them on the worktop as heat will dry them out and make them less tasty.
You should always store uncut watermelons in the fridge as they taste better chilled and they should be good if refrigerated for 2 – 3 weeks.
If you have cut your watermelons you should wrap them in plastic, this keeps the moisture in and stops them from absorbing the smell of other foods.
Cut watermelon stored wrapped up in the fridge should be good for 3 days.
What to do if your watermelon plant stops producing fruit
You may be having pollination problems so be sure to pollinate the flowers by hand because there will definitely be a lack of bees to do the job when growing indoors.
If you are growing more than one vine in a container then your watermelon plants may not have enough space, 12 inches apart is recommended.
If your plants are any closer than that and you may have to replant them so that they bear fruit.
The conditions for a watermelon plant to produce fruit have to be pretty near ideal.
Make sure your plant is getting enough direct sunlight, when growing indoors you may have to use an indoor grow lamp to ensure your plant produces fruit.
Don’t give up, fix the issues and fruit will grow eventually.
To grow a watermelon plant outdoors
When growing watermelons outdoors it may be a good idea to germinate your plant indoors then transplant it once any danger of frost has disappeared.
Plant your watermelons about 2 feet apart and if you are making several rows make the rows about 6 feet apart.
When your vines get over 2 feet you may want to remove the end buds to encourage branching.
Always plant and germinate several seeds in the one growing area then thin them out to keep only the most healthy vines.
Common watermelon plant problems and how to solve them
Watermelons are hardy plants but like all plants, there are diseases that can affect them. Here are some common watermelon diseases and ideas on how to treat them.
The quicker you act to fix the problems the easier it will likely be…
Powdery Mildew – This disease affects most plants and watermelons aren’t spared. It will look like the leaves have a white powdery coating on them and they will eventually turn brown and die. Pruning your plants to increase air circulation could solve this issue or alternatively use neem oil to treat your watermelon plants.
Downy Mildew – You will notice this type of mildew when angular spots start to appear on the leaves of your plant. They normally start as yellow spots that will turn brown with purple appearing on the underside of the leaves. This disease may reduce the amount of fruit produced but the fruit it does produce will still be healthy. To treat downy mildew apply neem oil and apply it at the recommended dose.
Anthracnose – This fungus is hard to detect initially, it will appear as small spots on the leaves and fruits of your plants. As this disease spreads the spots will get bigger and turn grey or black and sunken areas may start to appear on the watermelons. To cure this problem treat the plants with neem oil and you may have to rotate your crops to ensure future healthy harvests.
Gummy Stem Blight – This disease tends to affect older stems and leaves before it affects new growth. Black spots on the leaves and dark sunken areas on the stems and fruits are the first signs of this devastating disease. If you have wet or humid conditions while this disease is affecting your plants the plants could rapidly collapse beyond repair. You have to use a copper fungicide as soon as you notice any signs of gummy stem blight to have any chance of saving your crop.
Bacterial Fruit Blotch – This disease most often affects seedlings and young plants and will look like water spots on the leaves and fruits at first. As this disease spreads it will turn into black patches on the leaves of your plant. Most dramatically the fruits on your plant may begin to crack and a yellow liquid ooze out. Use a copper fungicide to treat bacterial fruit blotch as soon as you see any symptoms of this disease.
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