ORONO, Maine — Short, gloomy days, colder weather and long nights can mean just one thing for the garden enthusiast or farmer — seed catalog season is here again.

The advent of early winter signifies the time of year that mailboxes are filled with seed catalogs, their vibrant photographs and vivid descriptions of the flowers and vegetables a promise that spring is going to roll around again.

Lisa Colburn, an Orono writer whose book, “The Maine Garden Journal,” shares tips on how to make short-season, cold-climate ornamental gardening successful, said this week that she is excited to have already begun receiving seed catalogs.

“I call it armchair gardening,” she said. “I’ve started looking at them and making a list — a gardener’s wish list. I look forward to receiving the catalogs and seeing what their new selections are. I’m also disappointed when tried-and-true selections that I’ve depended on for a number of years are no longer available. It does happen with some frequency.”

Two of Maine’s largest seed companies, Winslow-based Johnny’s Selected Seeds and Fedco Seeds in Waterville, spend a lot of time and trouble getting their signature catalogs out the door and into mailboxes around the country and beyond. Staffers at each business said that making the decisions about what to include and what to drop can be difficult, and takes all year to do. Vegetable trends can catch even experts by surprise — for instance, what seed supplier could forget the great worldwide kale seed shortage of 2014? Choosing the correct assortment of seeds to entice winter-bound gardeners and farmers is both an art and a science, with a little bit of luck thrown in for good measure.

Pete Zuck, a vegetable product manager at Johnny’s Seeds, an employee-owned company, said that not that long ago, gardeners were pretty limited in what they could plant in their garden. Just a few varieties of even the most popular vegetables, such as tomatoes, beans and peas, were available. But in recent decades, the seed landscape has made a dizzying about-face. Now, the numbers of vegetable varieties available for sale seem limited only by imagination, and space in the various seed catalogs.

“You get to the point where there’s only so much you can fit in one catalog,” Zuck said. “We live in this world where customers expect choices. Breeding has become so sophisticated and competitive, there are an overwhelming amount of varieties … there are hundreds of companies breeding new things all the time. It’s a real race to develop the best stuff. Oftentimes things that people have come to trust get passed over for something better.”

It can be hard to tell growers that the cherry tomato they have loved for years is going away, he said, and so the company spends a lot of time communicating with customers and letting them sample new offerings when possible, he said.

Johnny’s breeds some of its own seeds, including those for pumpkins, winter squash, summer squash, tomatoes and peppers. They also purchase sample seed from vendors, which they plant in the spring and keep an eye on.

“The big thing about Johnny’s is that we don’t put anything in the catalog unless we feel we know it pretty well,” he said. “We want to give our customers enough information so they can be successful.”

By the end of the growing season, in late August and September, it is also crunch time for the catalog. Johnny’s employees work to figure out what types, and how much, seed to order, and then get ready laying out and printing the 1.3 million seed catalogs. Zuck said that even in this era of Internet shopping, a lot of people still rely on the printed version.

“Our catalog has a lot of information in it,” he said. “People use it as a kind of resource. It’ll be on the front seat of the truck. Farmers might want to place an order from the field.”

Over at Fedco Seeds, a cooperatively owned company that specializes in cold-hardy varieties that do well in the Northeast, division coordinator Roberta Bailey runs the seeds division. On a day when the Fedco warehouse smelled deliciously of butternut squash because a trial of that vegetable was being done, she said that taste is the number one trait that she looks for when it comes to ordering seeds for the catalog.

“It has to taste good,” she said. “That’s what growing food is all about.”

Choosing the best-tasting offerings is a long process. All fall, Fedco employees have been trying tomatoes, melons, carrots, daikon and kale.

“We taste all of them, cooked and raw, side by side,” she said. “We try to find varieties to replace the ones that are no longer available. If something didn’t do very well, we find other varieties and replace it.”

One time that taste wasn’t the deciding factor in carrying a line of seeds was when a company called Seminis was purchased by Monsanto, the world’s largest developer of genetically engineered crops.

“We decided not to buy from Seminis anymore,” Bailey said, even though that seed company had some of the best vigorous hybrid varieties in the world. “We spent years trying to replace them.”

She also said that vegetable trends can be challenging. A few years ago, for example, there was a sudden craze to grow celeriac, and Bailey had to reorder celeriac seeds from suppliers five times. Another year, a type of Italian polenta corn got some good press and suddenly started flying off the warehouse shelves.

“We couldn’t get enough,” she said. “Trends always surprise us. We’d be very wealthy if we could see the trends coming out of the gate. I don’t know what the next craze is going to be. It would really help me in my job if I knew.”

Bailey said that Fedco often will drop a variety of seed if they simply don’t sell very much of it and it doesn’t pay for the space it is taking up in the catalog.

“We try to give people a warning if it’s possible,” she said of the seed varieties that will get the ax. “One in a while, there’s enough of a hubbub that we bring it back.”