How to Plant Watermelons in Northwest Washington

Work the garden 12 inches deep with a garden fork or tiller. Incorporate 3 or 4 inches of compost or another form of organic matter and 3 to 5 pounds of 5-10-10 fertilizer for each 100 feet of row. Cover the area with a clear plastic tarp. Secure it with bricks or other heavy objects. The plastic warms up the soil and gets rid of weeds for the watermelon transplants. Prepare the garden in this manner in April. Watermelons require full sunlight conditions, especially in areas with cool summers like Northwest Washington.

Fill 4- to 6-inch peat pots with high-quality potting soil. Moisten the soil with water. Sow three watermelon seeds per pot, 1 inch deep. Perform this task during the first two weeks of May.

Set the pots in a warm, sunny area, such as in front of a south-facing window. Most watermelons germinate best around 80 to 85 degrees Fahrenheit. You can also use a seedling heating mat. If the indoor area is not sunny, use two 40-watt, cool white florescent lights that are kept 4 to 6 inches from the top of the seedlings. Keep the lights on for 16 hours a day. It takes five to 10 days for watermelon seeds to germinate.

Water often to keep the soil slightly moist. Once a week after germination, mix a liquid, balanced fertilizer at one-fourth to one-half the manufacturer's recommended rate into the water. For example, if you use a 10-10-10 balanced fertilizer, two or three drops per quart of water should suffice.

Snip off the weakest second and third seedlings with a pair of scissors if more than one sprouts. Do this about one week after germination.

Remove the plastic from the garden during the first two weeks of June. Form raised rows with the soil so they are 18 to 24 inches wide and 12 inches high, and 2 to 3 feet apart. Cover the rows with landscape fabric that will keep the soil warm and allow water to reach the roots. Cut holes in the fabric that are large enough to accommodate the peat pots. Transplant the seedlings by burying the pots up to their rims. Space the plants 2 to 3 feet apart. Water well with 1 inch of water after planting.