(A wee cross-post from Urban Homesteading hope y'all don't mind! I've got gardening on the brain this week!)
When I'm choosing what to grow in my garden each year, I try to make my selections based on two criteria.
First, I like to grow things that really are better homegrown. For example, peas start losing their sweetness the moment they're picked, so if you have your own you can pick them mere minutes before you eat them. And tomatoes...well, do I really need to defend the homegrown tomato? I think not!
Second, I like to grow things that are economical to grow. And if economy is your reason for having a garden, two of the best veggies to choose can be planted right now--onions and lettuce.
You can grow onions seed, sets (tiny bulbs), or seedlings (tiny skinny onions, also called "onion bundles"). I've never grown onions from seed--it's always seemed ridiculously time consuming--so unless you're a martyr get sets or seedlings. This year I bought 70 sets and about as many seedlings for less than $5.
Both sets and seedlings are easy to plant. First, as with anything, make sure your soil is prepared--add a little compost and dig around a bit to get it nice and mixed and loose. Then, I just use my fingers to dib a little hole into the ground. They only need enough space between them to form a full grown onion, so no need to get out the ruler--you can imagine the distance easily enough. Then plop your sets or seedlings into the ground, lightly cover them, and you're done. (A little bit of the seedling should be sticking out of the ground, and if the pointy top of a set is sticking up, that's OK too.)
In really dry years you may have to water them a bit as they're getting established, but on the whole I've found that onions can take care of themselves. The last time I remember looking, a bag of six or seven onions was about $4 at the store, so even if all but that many of mine died--not likely--I'd be breaking even.
Further, because onions store wonderfully, you can use them all year. Sweet Husband's grandmother used to keep hers hanging in old pantyhose. Just drop an onion in the toe, tie a knot, drop in another onion, and so on and so forth. Then as you need onions you can cut the hose at a knot to get them one at a time.
Another group of economical early crops are lettuces, including spicy mesculin and arugula. One of the little plastic, clamshell boxes of "spring mix" will set you back about $4 and lasts--in our house--about a week. But for the price of a $2 packet of seeds you can have lettuce all Spring.
To plant lettuce, sprinkle the seeds over nicely worked soil. (No soil at your house? Grow lettuce in a sunny pot or window box.) Gently tamp the seeds down and keep the soil moist until you start to see little seedlings popping up. Eventually, you'll need to "thin" your lettuce--picking out every other seedling or so once they start to look crowded--so that the remaining lettuce will grow big and strong.
(But don't throw those babies away! Because the thinnings? They're the super gourmet "microgreens" you see at restaurants, and they're incredibly tasty any way you want to serve them up!)
Once your lettuce is full grown and ready for eating, cut it off with scissors at its base without pulling up the roots. The lettuce will then grow up a second time for more salad eating pleasure, and will generally keep going until really hot weather hits and it gets bitter.