Planting Guide - Watermelon Seeds
Plant Watermelons In Your Garden
A long-trailing annual, watermelons are the poster child of summer! But not all are oblong and green with red flesh – the variety of watermelons available now cover many colors on the rainbow and in all different sizes. Large, traditional Garrisonian and Crimson Sweet are now accompanied by fabulous heirlooms such as Moon & Stars, Sweet Princess, and Yellow Petite. Grow what you know and love to eat during those hot summer days, but try some new varieties too – you may find a new favorite!
When & How to Grow Watermelon Seeds
If you live in a climate with a short growing season, consider starting your watermelon seeds indoors 4 to 6 weeks before transplanting seedlings into the garden. Sow watermelon seed directly, or set out your transplants 3 to 4 weeks after the last average frost date in spring.
Watermelon demands warm temperatures – both soil and air. Transplant or direct sow watermelon seeds only when the average soil and daytime air temps are at least 70F. Watermelons are heavy feeders and need soil rich in nutrients. They grow best in loose, well-drained, but moisture-retentive soil rich in organic matter. Amend your soil with aged manure, seaweed, and/or compost before planting.
Dig a hole 12” deep and 24” wide, fill with compost, manure and several handfuls of sand – this will create an area that is both moisture retentive and well-draining. Use the soil that was removed from the hole to create the mound and then sow your seed or transplant there.
Sow Watermelon seeds 1” deep, planting 4-6 seeds (or transplanting 2-3 of your strongest seedlings) in mounds that stretch 24” across. Planting on hills or mounds ensures that roots stay warm and the soil is well-drained. If direct sowing, wait until your young seedlings have developed three to four true leaves and choose to keep your strongest 2-3 plants by cutting the thinned out seedlings at soil level with scissors. If you pull out your weakest seedlings, you may disturb the tender roots of your remaining plants, so use of scissors or clippers is advised. Build mounds 5-10 feet apart.
We advise using a nitrogen fertilizer on your watermelon plants until flowers form. Then, switch to a high phosphorus and potassium fertilizer like liquid seaweed. Keep area well weeded, we don’t want our watermelons fighting for nutrients and water. Because this is a warm-season crop, it is helpful to mulch around the base – this will help with weed control and moisture retention.
Watermelons are 95% water and require plentiful, even watering for quick growing. Keep the soil moist until fruit reaches full size then stop watering while the fruit ripens.
Companion plants are corn, radish, beans, nasturtiums, marigolds, oregano. Bad companions are potatoes as they attract many of the same insects that feed on watermelon plants.
Avoid growing watermelon where night temperatures dip below 50 F; this will cause fruit to lose flavor. If temperatures exceed 90F for several days, flowers will drop without setting fruit. Watermelons require 70-90 frost-free days to reach harvest and will tolerate no frost. In cool or short-season regions, plan ahead by starting indoors or choose smaller varieties that come to harvest early.
Watermelon leaves commonly wilt in the afternoon sun, this is ok. If you see the leaves wilting before noon, immediately water as it is a sign of stress due to the heat and drought. Never allow the vine itself to become dry. A soaker hose or drip irrigation is the best way to water.
If you live in an area where the weather and soil are dry, try planting your watermelon in inverted hills rather than mounds. Make an inverted hill by removing two inches of soil from a circle 24” across, and use this soil to make a rim around the circle. This way, irrigation water or rainfall can be captured. We know lots of gardeners in Zones 9 and above use this technique for their watermelon, squash, beans, and many other summer vegetables.
Regular, even watering will help fruits avoid blossom-end rot which is caused by fluctuation of soil moisture.
Stop watering your watermelons about 10-14 days before the fruits are ready to harvest, this will concentrate the plant’s sugars and your watermelon will be sweeter. You may want to place a board under each melon to keep the fruit clean and dry. Watermelons will be ready to harvest after 70-90 days from sowing. Most people tap their watermelons and listen for a dull thump to know when the fruit is ripe. Other maturation signs include the ceasing of growth, the yellowing of the underside and the drying of the stem near the fruit’s base. Enjoy!