Fruit for the Month: September (Watermelon)


Crimson Sweet watermelon.
Photo Nina Gentle

This is another in my monthly series of posts about small fruits that can be grown sustainably in a (loosely-speaking) mid-Atlantic climate. I cover planting, pruning, harvesting and care of the plants, according to the season. I’ll give links to useful publications. We have a focus fruit, and then more about others that need attention during the month.

Watermelons are the focus fruit for September

Nothing beats a big slice of watermelon during a break from working in the fields. It’s a good cure for dehydration, especially if lightly salted to balance the electrolytes, and helps improve heat tolerance. It’s good to know watermelon are nutritious, but frankly, their main claim to fame is that they are delicious, and just about everyone wants one when the weather is hot.

Crimson Sweet Virginia Select watermelon.
Credit Southern Exposure Seed Exchange

I’ll start with information on harvesting, and pests and diseases to watch out for, then cycle round to things to think about for next summer’s watermelon crop.

Watermelon harvest

Ripe watermelons have mature seeds. In Crimson Sweet these are brown-black. White seeds indicate an under-ripe melon.
Photo Pam Dawling

The skill of the harvester in discerning ripeness is a major factor affecting the taste. The first sign we look for is the shriveling and browning of the tendril on the vine directly opposite the little stem of the watermelon. If this tendril is not shriveled we walk on by. Next we slap or knock on them.

According to Southern Exposure Seed Exchange, when a watermelon is ripe, it will have a hollow sound when you thump it with your knuckles: it sounds like thumping your chest. If it sounds like knocking your head, it’s not ripe; if it sounds like hitting your belly, it’s over-ripe. There is a 10-14-day period of peak ripeness for each variety. We harvest our Crimson Sweet from around 7/25 (75 days from transplanting) to the end of August. We might be still harvesting in September.

Lastly, we do the “Scrunch Test”: put two hands (heels together) spread out across the melon, press down quite hard, listen and feel for a scrunch – the flesh in the melon is separating under the pressure. Rumor has it that it only works once, so pay attention!

Other growers with other varieties use different ripeness signs, such as the change in color of the “ground spot” (the area touching the ground), or the change in rind texture from glossy to dull.

I like to cut the melon stems with pruners, but some people break them off. Watermelons need gentle handling, as do the vines if you will be returning to harvest again. After harvest, we set the melons out to the side of the row for pickup. This gives time for sap to start to ooze out of the cut stem. If the sap is red or orange, the melon is ripe. If it is straw-colored, the melon was cut too soon. This is useful feedback for new crew.

Post-Harvest Storage of Watermelons

Watermelon marked with a grease pencil.
Photo Nina Gentle

Watermelons can store for a few weeks, but then flavor deteriorates. We store ours outdoors in the shade of a building or a tree. Rotating the stored stock is a good idea. (Consider dating them with a grease pencil/china marker). The ideal storage temperature is 50-60°F (10-15.5°C), with 90% humidity.

Watermelon Pests

Compared to some crops, watermelons are not often challenged by many pests.

  • Striped cucumber beetles are our worst pest. They eat not only the leaves (which reduces the sweetness of the melons) but also the rind of the melons, leaving an unattractive russeted surface, thinner than it was originally, and easily damaged. Cucumber beetles can also interfere with fruit set by eating the stamens and pistils of the flowers. Don’t worry unless you see two beetles or more per plant.
  • Aphids (usually green peach aphids) can be a problem to young plants – another reason to use rowcover or fine mesh netting. If needed, use insecticidal soap, or import ladybugs or lacewings.
  • Spider mites can be a problem in hot dry weather if populations are driven into the patch by mowing of bordering grassy areas. Heavy rain, vigorous spraying with water or overhead irrigation will reduce numbers.
  • Root knot nematodes can attack roots and produce galls. This leads to loss of vigor and wilting.
Striped cucumber beetle in squash flower. Photo Pam Dawling

Watermelon Diseases

Organic growers do not usually get many disease problems with watermelon, provided the soil fertility is well-balanced and the plants are not physically damaged. There are a few diseases to watch for:

  • Alternaria leaf spot
  • Cercospora leaf spot
  • Gummy stem blight
  • Watermelon fruit blotch/bacterial fruit blotch is a serious seed-borne disease
  • Bacterial wilt – watermelon is resistant, although young seedlings could succumb.
  • Fusarium wilt is a persistent soil-borne fungal disease that infects the roots, invading the xylem cells.
  • Anthracnose is a fungal foliar disease that can cause loss of vigor and fruit spotting.

Check the Oklahoma State University Watermelon Diseases publication for help identifying diseases.

Planning Watermelon Varieties for Next Year

 After trying several varieties, we settled on Crimson Sweet, a 20-25 lb (9-11 kg) striped 10 x 12” (25 x 30 cm) oval OP melon which takes 86 days from transplant to harvest. It has tolerance to some strains of Anthracnose and Fusarium. Its flavor is the best! For many years, I saved the seed, selecting for size, earliness, disease resistance and flavor. This is available from Southern Exposure Seed Exchange, as Crimson Sweet, Virginia Select.

Crimson Sweet, Virginia Select watermelon seed collection.
Photo Pam Dawling

Charleston Gray is another popular large variety, with a redder color but less sweetness than Crimson Sweet. Black Tail Mountain (OP, 73 days) was made famous by Glenn Drowns, who developed it as a fast-growing, highly productive, rich flavored melon he could grow in a cold climate in northern Idaho. It stores for up to 2 months after harvest. OrangeGlo (85 days) is an outstanding orange-fleshed variety, with large fruits and great tropical flavor.

“Icebox” varieties are 6” (15 cm) round, 8-12.5 lbs (3.6-5.7 kg) melons, perfect for small refrigerators. Some varieties are ready as soon as 64 days after transplanting. Seedless triploid varieties Dark Belle (F1 75d) and Fun Belle are said to be better tasting than traditional Sugar Baby (77d) and orange New Orchid (80d). But triploid seedless watermelon seed is expensive and harder to germinate, and the transplants are very fragile and tricky to establish. Triploid varieties are hybridized from a cross between two plants with incompatible sets of chromosomes. This results in sterility (lack of seeds).

Even smaller than the icebox size are “mini” watermelons, 3-6 lb (1.4-2.7 kg). Golden Midget is an OP seeded mini from Baker Creek 70d, 3 lbs (1.4 kg). There are also triploid seedless varieties. Solitaire (triploid, 88d), is a single serving watermelon from Johnny’s. It has 6” (15 cm) diameter fruit. Harvest can begin 78 days after transplanting.

I’ll do a blogpost on growing watermelons next spring, once you might be sowing the seed, or at least planning your garden layout.

Other small fruits still available in September

Asian melons, Asian pears (must ripen on the tree), Asian Persimmons, Blackberries, Figs, Muscadine Grapes, Muskmelons, Pawpaws, Fall raspberries, Rhubarb.

Asian melons and muskmelons will only be available if you made a second sowing in June!

Other small fruits becoming available in September

Kiwiberries (Actinidia arguta, aka hardy kiwi, Chinese kiwi) and elderberries. American persimmons need to be soft before they’re nice to eat. This can be anywhere between September and February. If the wildlife are not going to wait for them to ripen, harvest them early and let them ripen indoors.

Sun Jewel Asian melon. Photo Mary Kranz

Other fruit care in September

Mow aisles, weed and water all fruit (weed blueberries and raspberries shallowly, so as not to damage roots).

Prepare and plant new strawberry beds in early September if not done in late August, using potted runners. If needed, use rooted runners from the paths of an old patch to fill gaps. Renovate strawberries to carry over for next season, if not already done.