Watermelons grow on thick vines. They can take up a large amount of space in a garden as they tend to spread out when planted. Some vines grow as long as 20 feet.
Watermelons are in the Cucurbitaceae family, which includes yellow squash, zucchini, cucumbers, pumpkins, cantaloupe and butternut squash. All of these vegetables and fruit also grow on vines, sending out vines quickly. They grow best in temperate climates, as they do not like cold weather. In fact, watermelons prefer soil over 70 degrees Fahrenheit. Most plants in this family should be spaced 3 to 5 feet apart to give them room to send out their vines.