Davis County Extension Agent Shawn Olsen has grown a field full of watermelons that will weigh 20 to 25 pounds and be ripe and ready to harvest before July 24 - several weeks before most watermelons in the state are ready for sale.

The early harvest not only means an early trip to market - and likely top dollar - but also a longer growing and harvesting season.In addition, Olsen says, experiments show a particular set of growing methods can produce a 20 percent increase in the number of watermelons harvested.

Olsen said farmers Grant and Duane Call, of Layton, asked him earlier this year to try several different planting and growing methods to try to produce an early harvest of watermelons.

"I planted Crimson Sweet, one of the best varieties, and used six different methods of planting and growing," Olsen said.

He planted seeds in small containers on April 20 and put the containers in a greenhouse for three weeks. He transplanted the young watermelon plants into the Calls' field May 15.

"I built an irrigation ditch on the ground and then spread a thin sheet of black plastic onto the field in a long row over the irrigation ditch with a transplanting machine developed Michigan.

"As the plastic was being put down, the transplanting machine automatically punched a hole in the middle of the sheet and placed a plant in the ground every three feet.

"Then, a sheet of white Reemay plastic - the material used for garment interfacing - was put down over the plant. The Reemay cover trapped heat and protected the tender plant from wind."

A second method Olsen used was to place the transplants in the ground by hand and spray the ground around them with black graphite to darken the soil and increase soil temperatures.

He also transplanted the watermelon plants into bare soil by hand and then covered them with a photodegradable clear plastic sheet to increase soil temperature.

In a second set of experiments, Olsen planted seeds in containers May 3 and let them grow in a greenhouse for three weeks and then planted them June 1.

Three different planting methods for the second batch of plants included putting the transplants into bare soil without any cover or graphite spray; covering the transplants with photodegradable clear plastic; and spraying the soil around the plants with black graphite.

The best method, by far, was putting transplants into the black plastic sheets May 15 and covering them over with Reemay.

The second best method appears to have been the early planting and covering the transplants with clear plastic. Olsen said there is some evidence that plastic traps carbon dioxide near the plant and increases photosynthesis.

The cost of the plastic and Reemay and the labor of transplanting is far outweighed, Olsen said, by the 20 percent increase in harvest and the early harvest and longer growing season.

He said farmers in Oregon are using plastic ground covers on about 5,000 acres of watermelon and are achieving early harvests and larger than average yields.

While the graphite treatment does not seem to be particularly successful in these watermelon experiments, Olsen said, graphite does work well with other plants. He is working with Utah State University Extension soil specialist Terry Tindall on other growing projects and, on pastures and on small grains where the farmer wants a rapid and early snow melt, black graphite works well.

While most danger from frost is over by May 15, Olsen does not recommend transplanting watermelon plants that early without plastic protection. The normal planting time for watermelon transplants, he said, is the first of June and the normal time to plant watermelon seed is May 15.

The black plastic sheets cannot be used again, he said, but the white Reemay can usually be used for two or three years.

Watermelon farmers using irrigation, especially with plastic cover, can use furrow or drip irrigation, or an overhead sprinkler system with equal success, he said.