How to turn a small terrace garden into a sweet watermelon patch this summer

If you've ever tried to wedge a 20-pound watermelon into your grocery cart, you would know that this fruit has a space problem. It is fair to ask if a plant that can send vines ten feet or more across an open field can ever work on a city terrace. According to Utah State University Extension, watermelons really just need three things to grow well: strong sunlight, warm soil, and fertile ground that drains easily.

That’s not limited to sprawling backyards. With the right container, the right variety, and a little patience, a terrace, balcony, or fire escape can become a real watermelon patch this summer.

Start with the right container, not the biggest one
Skip the idea that you need a raised bed the size of a kiddie pool. What actually matters is a container that is deep and wide enough for the roots to spread out comfortably. Vegetables grown in pots can be successful in almost any small setting, from a window box to a stretch of sidewalk, as long as they get enough light, water, and room for their roots, according to Clemson Cooperative Extension's Home & Garden Information Center.


But the guidance also suggests that dwarf and miniature varieties generally flower and fruit earlier than the full-sized varieties, although the harvest is not quite as heavy overall. That is a fair tradeoff for terrace growing, so look for compact or bush-type varieties of watermelons rather than the classic sprawling type.

Give it sun like you mean it
Watermelon plants are not shade-tolerant roommates. The Home & Garden Information Center at Clemson Cooperative Extension says fruiting vegetables need at least five hours of direct sunlight per day to do well, and they do noticeably better with eight to ten hours. A corner of a terrace that receives a few hours of dappled afternoon sun will probably produce lots of leaves and not much fruit. Place your container in the sunniest spot on your railing or ledge, and turn it around once in a while if one side gets more light than the other.

Get the soil temperature right before you plant
Timing trips up more new gardeners than almost anything else. Utah State University Extension says watermelon seed should be planted when the soil temperature reaches about 65°F, because cooler soil slows germination. In many areas, that means late spring, once night temperatures have moderated. You can take the guesswork out of it by sticking a basic soil thermometer a couple of inches into the potting mix.

Water deeply, then ease off near harvest
These plants like one good soak, not frequent light sprinkles. Utah State University Extension recommends deep and infrequent watering, about 1 to 2 inches a week, so the moisture reaches the root zone, not just the surface. It is helpful to remember why the plant is so demanding: according to Clemson Cooperative Extension’s watermelon factsheet, the watermelon itself is about 92 percent water. As the melon approaches ripeness, Utah State University Extension recommends reducing the watering to concentrate the sugars and add a little more punch to the flavor instead of watering it down.

Feed it, but don't overdo the nitrogen
Once the vines send out runners, it's time to side-dress with fertilizer. Utah State University Extension recommends the first nitrogen application just as runners show. Clemson Cooperative Extension’s watermelon factsheet separately recommends a follow-up feeding after bloom, once fruit is developing on the vine, and warns that overdoing nitrogen pushes the plant towards excess vine growth instead of fruit. That warning is especially significant in a container, as sprawling vines are the last thing limited terrace space can accommodate.

Know when it's actually ready
This is where the impatience gets the better of most first-timers. According to Utah State University Extension, there are three sure signs that a melon is ripe: the small curly tendril nearest the fruit’s stem dries up and turns brown; the light-colored spot where the melon rests on the ground turns from white to yellow; and the rind goes from shiny to dull. None of these is foolproof on its own, so checking all three together is the safer bet.

A small harvest, a big reward
A terrace-grown watermelon isn't going to break any records, but it doesn't need to. Even one healthy container plant can still provide you with a really sweet, homegrown fruit, and it has a good nutritional return, too. Utah State University Extension says that a two-cup serving contains about 80 calories and is low in fat, but is a strong dose of vitamin A and vitamin C. That's a pretty good return for a pot, some sun and a summer’s worth of patience.