January (in the Northern hemisphere), when the garden is covered with snow and seems most dormant, is the time to start planning the garden and poring over seed catalogues. It takes time to work out a garden plan and choose the vegetable varieties you want to grow. And then it takes time for your seed order to be filled and delivered. Add to that the head start you may want to give some plants indoors before planting outside, and midwinter becomes none too early to start. Nevertheless, any time before the last practical planting date for the varieties you want to grow will do. Seed companies will generally take your order well into spring, and plenty of seed packets can be found on the racks of local stores at that time.
When perusing seed catalogues, try to pick vegetable varieties you think you would actually want to eat.
Know which planting zone you are in. Most seed catalogs contain zone maps, or you can call your local agricultural extension, usually affiliated with a state college or university. If you are just starting out, try crops that are relatively easy to grow. Peas, beans, lettuce, radishes, and tomatoes are good choices. Stay away from peppers and melons at first unless you live in a warm area.
Draw up a garden plan. Read about the vegetable varieties you selected, and determine how much space is required for each. If you’re not mentally prepared to thin small plants, only plant one seed where you wish each adult plant to grow. Otherwise you might wind up with plants that are too close together to thrive. And if you plant more than what will yield what you can actually eat or give away to freinds, you might be in the sad position of having to compost perfectly good vegetables. The alternative to that is canning, drying, or otherwise putting up food into storage, which may be more work than you want.
Ideally, the ground has been prepared the autumn before planting. Weeds and dead crop plants have been removed, and a layer of compost has been applied. Of course, these things can be done in the spring as well, once the ground has thawed sufficiently.
Most gardeners work the compost into the soil, either with a rototiller or by hand with a fork or spade. Some do not turn the soil at all, on the theory that soil structure is better when it develops naturally.
Of course, there is no reason not to add ammendments after the spring thaw. But it’s easier if the seedbed has already been prepared. That way, the garden can be direct-seeded as soon as the top layer of soil has thawed. Thawing of the soil can also be hastened using black plastic or other coverings.
Peas can be planted as soon as the soil has thawed sufficiently to poke a hole an inch or so deep. Other cold-hardy crops, like radishes, broccoli, onions and lettuce can be planted when the ground has thawed enough to start drying out on top.
Start crops indoors early if the instructions on the seed packets call for it. Then use row covers, cloches (even an inverted jar will work), plastic bags, cold frames, or whatever you can to aid the transplants through the difficult hardening-off period. Take seedlings inside at night before transplanting, especially if the temperature drops. Don’t expose transplants to too much sun at first: They may scald. And use mulch. A couple inches of straw around the base of plants keeps weeds down, moisture in, and helps control soil temperature once the ground has warmed.