Gardener: Plant heirloom seeds indoors to jump-start spring

Winter is the perfect time to think about next spring's garden. I have a fascination with heirlooms (plant varieties generally over 50 years old and typically passed down through generations), so my plans always include plenty of these.

I've been starting heirloom seed varieties for years, and I still get a thrill when something so tiny and dry -- and with such an interesting history -- actually grows into a vibrant, living plant.

There are practical reasons for starting from seed, too. Mature nursery plants are expensive, and not many unusual heirloom varieties come ready to transplant. So starting heirloom plants from seed is often the only way to save these unique varieties for future generations.

There are plenty of catalogs and websites for folks who grow, sell and share these old fashioned favorites. The Seed Savers Exchange of Iowa, www.seedsavers.org, Virginia's Southern Exposure Seed Exchange, www.southernexposure.com, and Native Seeds/SEARCH of Arizona, www.nativeseeds.org, are good places to begin your search.

Timing is everything when you're starting seeds indoors. Start too soon, and the plants outgrow their containers and end up needing more light then a typical indoor home can provide. Start too late, and you'll have small seedlings that have to be pampered to survive.

The key is the last frost date in your area. Plants set out after that should be safe. Ask the extension service when your last frost date is expected or insert that search term for your area online.

Find the number of days the seed takes to germinate and grow enough to set out; retail seed packets include this information on the label. Then back time planting from there.

For example, the 1938 AAS winner heirloom summer squash Early Prolific, available from Baker Creek Heirloom seeds, www.rareseeds.com, takes 45 days. If your last frost date is April 10, count back and start the seeds on or around Feb. 25.

Start seeds in most any well-drained small container. Butter tubs, plastic bakery boxes, even pizza boxes are fine. Use a sterile seed starting mix rather than garden soil. The latter is full of disease organisms and too dense to let young roots develop properly. Moisten the soil-less mix with water to the consistency of fresh brown sugar. Fill each pot to 1/4 inch from the top.

Heirloom seeds may not sprout as well as hybridized seeds, so plant three or four and thin out the weakest later. Cover lightly with additional soil-less mix. Refer to the seed packet for proper sowing depth. The top of the refrigerator supplies important bottom heat for good germination, but a commercial heating mat gives a more consistent temperature. Plus I like to have my containers in sight to keep an eye on all the action.

The instant the seed sprouts break the soil surface, sufficient light is critical. Ordinary fluorescent shop lights work just fine when hanging an inch or two above the leaves. You could use one warm-daylight and one cool-daylight tube to provide the full light spectrum, but personally, I haven't found it to be worth the extra expense over standard 40-watt tube bulbs. Set a timer to give the plants 16 to18 hours of light. Raise the lights as the plants grow to keep the lights about an inch or two above the leaves.

Wait until after the first true set of leaves have developed before feeding with diluted amounts of soluble fertilizer in warm water (three-quarters to one-quarter strength or less), gently pouring at the side of the pot to leave the tender young plants undisturbed. Seedlings are too delicate to set directly into the spring sunshine, so harden them off over two weeks, starting with four hours of sun and adding a half-hour every other day until they're getting a full eight hours.

Heirloom seeds are like kids -- give them the right conditions and they do the rest. With a little warmth, the right moisture and light and a bit of patience, and you'll raise a crop of healthy, garden-ready heirlooms that can't wait to start growing and pass on their gardening legacy.

Joe Lamp'l, host of "Growing a Greener World" on PBS, is a Master Gardener and author. For more information visit www.joegardener.com.