A handy and simple way to prolong your garden's life into winter -- and help get it started earlier in the spring -- is to build a cold frame with hay bales and old window frames. There's no need for hammer, nails, screwdriver -- just a little ingenuity.

Bales of rained-on hay or dry straw are usually available at garden centers, farm co-ops or local farmers. Four bales will provide a cozy area of about 16 square feet in which to grow hardy lettuce, parsley, spring onions, radishes and spinach.

Set the bales on their sides -- that is, with the stems vertical, rather than horizontal -- to allow drainage for rain and melting snow and to provide extra height. Bales should touch one another to keep wind out.

Discarded window frames are available from junkyards and used-furniture dealers. You can build the cold frame in the vegetable garden, where, presumably, the soil is already well built-up and has plenty of nutrients. Build the cold frame close to the house to cut down on slogging through mud and snow. The south wall of a shed or garage will help keep down wind and will retain and reflect the sun's heat.

If your garden's too far away or there's no convenient wall, you'll have to build your cold frame on new ground. Fill it with a six-inch layer of topsoil and add compost. The soil doesn't have to be very deep, since you're sowing shallow-rooted crops that will be harvested when they're quite young.

Maintaining the cold frame is fairly simple: Slide back the window frame or prop it open on warm, sunny days to allow air circulation and keep condensation from building up. On cold days and at night, keep it closed. Snow should be brushed off to let in light and sun. If you want to get fancy, set some two-by-fours on the back bales so that the closed window will slant, allowing rain and snow to run off.

You can sow seeds in the ground or start them indoors in a sunny window and move them outside when the seedlings reach three to four inches.

Keep in mind that this type of cold frame is temporary. In the spring, you can take it apart and break up the bales for mulch. To make a semi-permanent cold frame, use scrap lumber: Make the back higher than the front and hinge the window frame. A more permanent -- and more effective -- cold frame is dug into the ground. Dig a pit about a foot deep and build the cold frame. You can get fancy windows and special heat-sensitive mechanisms that open the window automatically, but that's another column. NOTE: While you can grow parsley very successfully in a cold frame in the winter, don't try to transplant mature plants from the garden to your cold frame: The taproot's too long. You may find seedlings available at plant stores or herb specialists or you can start seeds on a sunny windowsill; they're slow, so don't give up. Overnight soaking before planting helps speed germination.

Where you can always find earthly delights in Washington:

DUMBARTON OAKS -- 31st and R streets NW. Open 2 to 5 daily. Admission is $1 through this weekend, but free admission begins in November and continues through March. Call 338-2878 for a recording of what's blooming and where to park.

KENILWORTH AQUATIC GARDENS -- Kenilworth Avenue to the Quarles Street NE exit and follow signs. Or take Metro's Oragne Line to the Deanwood exit, cross Kenilworth Avenue by the pedestrian overpass and go one block down Douglas Street. Free admission 8 a.m. to dusk. More than 40 species of plants, featuring waterlilies and lotuses. For more information call the National Park Service at 426-6700.

NATIONAL ARBORETUM -- at 24th and R streets NE, off of Bladensburg Road. The 444 acres of hills and lawns are Open 8 to 5 Monday through Friday, 10 to 5 Saturday and Sunday.

U.S. BOTANIC GARDENS -- at Maryland Avenue SW (First and Canal streets) at the foot of Capitol Hill. Open 9 to 5 daily. Three blocks from orange/blue line Metro stop Federal Center SW. Tropical and subtropical plants.Phone: 225-8333.