Long-season vine crops such as melons and squash can be started early in the season if you adequately prepare and warm the soil. The right preparation will ensure even growth and ample yield.
Melons, watermelons, winter squashes, and pumpkins can require 125 to 160 days from sowing or transplanting to harvest. Getting an early start will ensure a harvest in short summer regions and perhaps two or more harvests in longer summer regions. Success is dependent upon warm soil early on and even moisture throughout the season.
How to Start Long-Season Vine Crops Early:
• Grow melons and squashes in raised beds or on hills or mounds that warm early in the season. In late spring, about the time of the last expected frost, dig holes about 18 inches deep and wide. Throw a handful of bone meal or all-purpose vegetable fertilizer (or half a shovelful of aged steer manure) into the bottom of each hole then backfill with a mix of aged compost, sand, and native garden soil or a half-and-half mix of store-bought planting mix and native soil.
If you are not planting in a raised bed, top each hole with the same mix to form a mound about six inches high and a foot or two wide. Water in the soil and cover the bed or mound with black plastic sheeting (plastic mulch) or black landscape fabric that will absorb solar heat. Let the soil warm up for 10 days or more before sowing or transplanting.
Preparing plants holes and mounds with aged compost is important for the success of melon and squash crops—more important than feeding plants later in the season. Compost and planting mix are rich in water holding humus. Consistent moisture is necessary for vine development and essential for fruit formation. Humus releases moisture evenly to plant roots.
• Sow seed outdoors or set out transplants after the soil has warmed to 65°F, usually two or three weeks after the last frost. Starting seed indoors and setting out transplants will provide an earlier harvest. Seedlings for transplanting should be started indoors three to four weeks before the last expected frost and set out when about six weeks old. Whether transplanting out or sowing seed in the garden, cut slits in the black plastic four to six feet apart for planting—the distance between plants at maturity. Pull the plastic back enough for sowing or transplanting.
If you sow seed in the garden, sow four to six seeds per hills. Sow seed two inches apart and cover with one-half inch of soil. Keep the black plastic in place and also cover seeds with a bottomless plastic milk jug–to warm the soil even more. Let the jug cover seeds until they germinate and for a week or two after. Seed will germinate in about two weeks. After seedlings are three to four inches tall, thin the number of seedlings to the three strongest plants per mound. Replace the plastic jug with a floating row cover to protect plants from cool weather and insect pests (such as cucumber beetles) as they grow. When the first female flowers open, remove the row covers so that bees can pollinate flowers.
• Once the soil has warmed and plants are growing, the black plastic mulch can be removed and replaced with an organic mulch of dried leaves, straw, hay, or dried grass clippings. (Don’t use fresh or wet grass clippings; they will mildew.) Mulch will keep down weeds, slow soil moisture evaporation, and slowly decompose adding nutrients to the soil. Make sure the organic mulch you use is pesticide and weed seed free. If you warmed the soil with black landscape fabric, there is little risk the soil will grow too warm during the summer; leave the fabric in place and forego organic mulch. The fabric will protect plants from soil rot as they mature.
• Keep melon and squash plants evenly moist throughout the growing season. Do not let the soil dry out more than four inches below the surface. Water any time plants begin to wilt before noon. Feed plants with a side-dressing of compost tea or fish emulsion two weeks after seedlings appear or at transplanting time; feed plant again when the first flowers appear.
• When melons and squash begin to grow large, raise them off the soil and rest them on wooden shingles, clay roof tiles, sheets of plastic, or overturned cans to prevent contact with the soil and rotting.
• Melons are ready to harvest when they smell sweet and separate easily from the vine; watermelons are ready to pick when the underside of the fruit turns creamy yellow and the tendril at the stem end turns brown. Harvest summer squash when they are still small just 4 to 6 inches long. Harvest winter squash when the skin is so hard that it can’t be pierced by a fingernail. Harvest all melons and squash before the first hard frost.
Cure winter squash for storage by placing them in a hot, dry place for three weeks. Curing will toughen the skin so that they will keep through the winter.
More tips at How to Grow Melons.