Pumpkins don't grow on trees.

It just seems they might to city folk when thousands of potential jack o'lanterns suddenly appear in October at roadside stands and supermarkets in and around American's cities.

They grow on vines, usually in small fields within easy shipping distance of their urban markets, and in a good year they can grow so thick that a field seen from a distance glows orange in the sharp full sun.

In a good year like this year is an acre can produce about 15 tons of pumpkins and a ton of pumpkins sells for about $85 at Washington's Northeast Market.

That can mean a handsome profit for a farmer like George B. Cochran who has 25 acres in pumpkins in fields around Purcellville, Va.

Cochran said he could clear $700 an acre on his pumpkins after paying sales commission, rent on land, pickers' wages, rental on a truck, the cost of pesticides and fungicides and other expenses.

"If I can get them all sold, I'll be all right," said Cochran, 67, who is now in his fifth year raising of pumpkins.

If he can't get them sold, his profit margin will rot away in the field, food for deer and groundhogs.

Pumpkins are what the U.S. Department of Agriculture calls a "speciality crop," and as such it presents some special problems for growers and sellers.

The biggest problem is Halloween. A nice fat pumpkin may be worth $1.79 today, but on Nov. 1 its commercial value plunges to a nice fat zero. And unlike wheat or corn, a farmer can't store pumpkins until the price rises.

Cochran, who has lived in Loudoun County since 1940, and sold eggs before he began growing a wide range of vegetables to sell wholesale and at his stand in Purcellville started this year's crop a year ago when he took the seeds out of about 500 pumpkins, dried them and stored them for spring.

These seeds, Cochran said, "are the only secret I have." He bought five pounds of seed for what he calls "an exceptionally good pumpkin" two years ago and now uses that strain for most of his crop.

He planted in early June and battled weeds until the vines got a good start and then battled bugs until harvest time.

"Don't let anybody tell you crops can be raised without sprays and weed killers," Cochran said. "No farmer likes to pay to put the damm stuff on, but organic farming is just a myth."

Now he has eight men and women stacking pumpkins in piles in the field, then loading them on a truck for the drive to Washington where Clifford Himes sells them on commission to small retailers. The supermarket chains buy separately for themselves.

Cochran's wife Emily sells them at retail for 12 cents a pound at the vegetable stand and also has a "pick-your-own" field where $1.75 buys your choice of pumpkin.

In town, prices vary widely, from 25 cents a pound for little ones to $1.79 for a big one that might weigh 50 pounds at one supermarket to a flat 12 cents a pound at another chain.

"If I could get 10,000 pick-it-yourselfers, I'd be in business," Cochran said as a school bus full of kindergarten children pulled in to pluck petite pumpkins.

"But we haven't had a good run because we've had such lousy weekends," he said. "If we could get that field cleaned out I could haul pumpkins from another field and set 'em out to be picked," he laughed.

"It'll take a truckload a day to get them all hauled," said Cochran who is worried about competition from Pennsylvania creating a surplus here.

Himes, a commission merchant, confirmed that Pennsylvania farmers have a good crop too. But a good crop doesn't mean a good year. "I know a man in Pennsylvania with 85 tons and not a pumpkin sold," he said.

National and state statistics on pumpkins are scarce and a USDA official said the department's crop reports "go from peppers to spinach with nothing in between. It is such a highly seasonal item there hasn't been too much attempt to measure it."

There is one other thing about pumpkins, according to the USDA. If you have a great big one grinning on your front porch, it's probably a Cucurbia Maxima.

And, a USDA expert said, that's not a pumpkin at all. It's a squash.