Watermelon
Citrullus lanatus
The one crop where thumping really is a legitimate technique, though the ground spot is better.

Heat, space and time
Full-size watermelons need a long hot summer and a lot of room - eight to ten feet of run per plant. Icebox types of six to twelve pounds finish two to three weeks sooner and suit a smaller zone 6b/7 garden much better.
Warm soil and black plastic
Do not sow until soil is at least 70F. Black plastic mulch raises soil temperature several degrees, suppresses weeds and keeps fruit clean; it makes a bigger difference to watermelon than to almost any other crop here.
Seedless types need a pollinator
Triploid seedless varieties produce sterile pollen and must be planted alongside a standard diploid variety to set fruit - usually one pollinator for every two or three seedless plants. Plant seedless alone and you get flowers and nothing else.
Water heavily, then stop
Consistent deep watering while vines run and fruit sizes, then cut back sharply once fruit reaches full size. Dry finishing concentrates sugar; late heavy rain or watering causes splitting and bland flesh.
Three ripeness signs, used together
The tendril nearest the fruit stem dries and browns; the ground spot where it rests turns from white to deep buttery yellow; and a thump gives a low hollow sound rather than a high dull one. Watermelon does not slip from the vine, so you have to judge it.
No ripening after picking
Unlike a muskmelon, a watermelon does not sweeten at all once cut. Picking early is a permanent mistake, so when in doubt wait a few more days.
Pests and disease
Cucumber beetles and the bacterial wilt they carry, aphids, and anthracnose in wet years. Fusarium wilt is soil-borne and persistent - rotate on a long cycle and choose resistant varieties if it appears.
Storage
A whole uncut melon keeps two to three weeks in a cool room, rather less in the fridge, where very cold storage degrades the texture. Refrigerate cut melon and eat within a few days.
- Days to harvest
- 70-100
- Spacing
- 36-60 in
- Row spacing
- 6-8 ft
- Sun
- Full
- pH
- 6.0-6.8
- Soil temp
- 70F+
- Ripe sign
- Yellow ground spot
- Storage
- 2-3 weeks