In seed starting, timing is everything. By late winter, the cold frame at Dumbarton Oaks’ greenhouse is full of transplants that were started in early February. Cool-season vegetables such as kale, broccoli and chard can be started now, but wait for tomato seeding. (Luis Marmol/Dumbarton Oaks)

The days are lengthening, and gardeners are getting twitchy. My green-fingered friends are doing a lot of plant planning and seed ordering while trying hard not to start things yet, although that day is almost here. Here, that is, for cool-season veggies that can go out as transplants before the last frost and with protection.

To state the obvious, we are weeks away from popping a tomato seed into a foam cup. As for eight-week-old transplants of tomatoes and other warm-season creatures such as peppers and cucumbers, they shouldn’t see the open garden until May.

It is easier than ever to find transplants started commercially in the spring, even if many retail sources make too much tender material available too early. It is far more convenient to pick up a broccoli plant in a four-inch pot in April than to start one yourself at this time of year, but you’d be missing a lot of the fun of the enterprise.

There are a number of good sources of seed-starting schedules for our part of the world, including one from Southern Exposure Seed Exchange. Also check out the video clips of indoor seed starting from the Maryland Extension Service’s Grow It, Eat It Web site (extension.umd.edu/growit).

I asked Laura Schumm, a vegetable gardener at Lewis Ginter Botanical Garden in Richmond, what schedule she follows, and she sent me the seed calendar assembled by her colleague Heather Veneziano. Their efforts start this week with celery and a few container-grown peas for the children’s garden. (At home, peas are probably best sown directly in the garden at the end of next month.)

The author tests the viability of old lettuce seed, wrapped in moist paper.. (Adrian Higgins/The Washington Post)

By mid-February, however, Schumm and Veneziano will have sown seeds of spinach, arugula, parsley, turnips and even lettuce.

In the handsome Palladian greenhouse range at Dumbarton Oaks (alas, behind the scenes), I found Melissa Brizer and Luis Marmol clearing the decks for their imminent seed-starting endeavors. They have a tried-and-trusted regime of starting early stuff such as celery, brassicas and onions in the next week or two. In a month or so, they will pot up the seedlings from 72-cell flats to individual pots, before moving them to a barely heated cold frame in March. Here the transplants will harden off for a couple of weeks before making it to the vegetable garden, where visitors can then watch their progress.

“If you start too early,” Brizer said, “they just get leggy.”

They have the luxury of a greenhouse. Trying to start veggies on a windowsill is like beating your head against a wall. In January I dust off my homemade seed-starting apparatus — four decks of plywood, each bathed by a pair of fluorescent shop lights — see what trays are serviceable and start filling them with blocks of seed mix and seeds. The cellar thus becomes an unlikely but cozy wintertime ark.

I have found the perfect veggie for gardeners who want to jump the gun a little: the leek. Last week, I dropped 150 seeds of the varieties Bandit and Tadorna into three seed trays. I will plant them out as baby leeks in early April, and because both are winter-hardy I intend to harvest full-size leeks from September through to the spring of 2016, with a bit of luck.

I have always found onions to be grudging in Washington — a product of our latitude and climate — but each winter finds me pouring these black grains into seed trays. They are indistinguishable from leek seeds and a reminder that keeping track of varieties and labeling them is fundamental to the business of seed starting. As with leeks, you can sow them anytime in January because their transplant size is so fungible.

This is also the moment to start the related cabbage, cauliflower, kohlrabi, kale and broccoli. The last three are fairly dependable, but growing cabbage and cauliflower is a bit of a tightrope act in getting them to head nicely before the heat sets in around Memorial Day. The key is to grow them well — regular watering and a little organic feed — but the key too is to have sturdy and well-conditioned transplants ready to put in come late March. That means sowing them now.

I tend to sow lettuce directly into the garden in mid-March, but I might be tempted to start them indoors this winter, as some do, though not before mid-February.

Most of my seed is from last year or even the year before, but I keep it in a spare fridge and it stays fresh for two or three years. Last fall, I left some seed of choice Italian varieties of lettuce in the tote bag I cart to my garden, and the odd rain shower moistened the packets. The instinct was to throw them out because wasting time with dud seed is the falsest of economies.

But testing the viability is a simple endeavor at this time of year: I arranged 20 seeds on a paper towel, folded the sheet like a letter, tucked it into a plastic sandwich bag marked with the variety, and moistened it. The idea is then to set the bag somewhere warm and wait a week. I use a seed-starting heat mat, which is a must if you are germinating eggplant and pepper seeds, by the way. If half or more of my lettuce seeds sprout, I’ll keep the packets. If not, I’ll order afresh.

By checking your old seeds in this fashion now, you have the luxury of time — time to assess the germination rate, time to buy new seed if that’s necessary.

In early summer, when the day lengths start to get shorter again, those red cabbages will be ready for plucking. The idea that you started them back in early winter from a grain of dormant life you held in your hand will make them especially delicious.

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