How to Grow Square Watermelons Indoors

Choose a type of watermelon. Depending on their breed, watermelons may range in weight from a few pounds up to 50 or more. People who plan to grow square watermelons indoors should consider the amount of available space before choosing a particular variety. In most cases, smaller melons, such as Garden Baby, which can be grown in plots as small as 2 feet by 2 feet, will do better indoors than especially large breeds, which require greater amounts of space. According to VegetableGardener.com, some of the larger, 25-pound melons require growing spaces of at least 4 by 6 feet per plant.

Create the garden. Place a large plastic tarp or child's swimming pool on the floor of the room in which the watermelon plants will be grown. This is especially important for rooms that feature hardwood or other types of floors that could be damaged by water leaks. Position a large wooden box that is at least three feet wide, three feet long, and 15 inches deep on top of the tarp or inside the pool, and fill it with high-quality topsoil. If using a child's swimming pool, be sure to look for a product that is larger that the size of the wooden box in which the plants will be grown. Most pools can hold wooden boxes that are 3 feet by 3 wide wide--however, larger pools may have to be special ordered.

Plant the watermelons. If growing the plants from seeds, they must be pushed into the soil at a depth of approximately one inch, and should be placed no closer than two feet away from each other. When planting watermelon seedlings, dig a hole around three to four inches deep in the soil, and carefully place the seedling inside. Pack loose surrounding soil up and around the sides of the plant. As with watermelon seeds, seedlings should be planted no closer that two feet apart from each other.

Care for the plants. Since the plants will be indoors in a climate-controlled space, the time of year at which they are planted won't make too much of a difference, especially if air temperatures are kept between 70 and 80 degrees Fahrenheit. People who are growing watermelon plants indoors should ensure that the garden receives plenty of light. This can be done either by placing the growing space in a room that receives full sun exposure or by shining a spectrum grow light on the watermelon plants for at least six to eight hours per day. Finally, ensuring soil pH levels are kept between 6.0 and 6.5 by using the appropriate types and amounts of fertilizer at all times can boost plant growth.

Shape the melons. To form square watermelons, the fruit must be grown inside a square glass box. Glass boxes such as these can be found at home improvement or gardening stores. Ideally, these boxes should be slightly smaller than the predicted size of the mature melon and composed of tempered glass that is open on one side. The square box must be placed over the melons as soon as they appear on the vine to ensure appropriate growth patterns, and not moved until the melons are harvested.

Harvest the square watermelons. Since the melons are grown in a square box composed of tempered glass, harvesting can be a challenging. When the watermelons appear ripe, cut the vine from its attachment point at the bottom of the fruit. Using caution, tap one of the edges of the box glass box surrounding the watermelon with a hammer. While most tempered glass is quite strong, the edges are surprisingly fragile and will break with a small amount of force. Stand back after tapping the edge of the box, as small chunks of glass may continue to fly from the box even after the initial break. While wearing work gloves, brush all pieces of glass from the outside of the square melon. Be sure to wash the melon thoroughly after harvesting, and store in a cool, dry place.