How to Grow Crimson Sweet Watermelon Indoors

Fill a large 5-gallon plant pot with a mixture of well-mixed, equal parts of sand, dampened peat moss and compost. The peat moss will hold the moisture while the sand allows the extra water to drain. Humus is a good source of nutrients for the watermelon -- without the bugs that you might find in compost.

Water the soil gently over the top until it starts draining from the bottom. This also settles the soil, and you might have to add more soil to fill the pot.

Plant a seed or seedling in the middle of the pot. Only try growing one plant indoors since it will take so much room to grow. Firm the soil around the roots or the seed to make good contact.

Set the pot in the sunniest spot in your house. They need at least six hours a day of direct sunlight and a room temperature of 80 to 85 degrees. Water the plant daily to replace the water taken up by the ever-elongating vines and the large leaves.

Allow plenty of space for the vine to grow for the next four months. Plan to use a trellis least 8 feet high. Prune the vine with clean pruning shears to force energy into the developing fruit. Leave only one stem and remove any laterals after the eighth node when the fruit has reached golf ball size. Secure the hanging melons in a mesh bag to reduce the strain on the stem.

Harvest the watermelons when the underside of the melon is looking slightly yellow instead of green.