Some seeds need moist cold; others need nicking

“Stratification” means supplying a period of moist cold to trick seeds into thinking that they’re experiencing winter. If you’re sowing indoors in spring, presoak the seeds, then place them in a zip-top, plastic, sandwich-size bag filled halfway with moist, seed-starting medium. Top off the seeds with another inch of moist medium, and then put the bag in an undisturbed corner of the refrigerator (at 34°F to 41°F). Check weekly for signs of germination. When the seeds begin to sprout roots, carefully transfer them to pots, fishing each seedling out of the bag with a spoon to keep soil around the new roots and to avoid disturbing delicate new growth. Then, care for them as you would any other seedlings.

Seeds that require cold treatment can also be planted outdoors in fall or stored in a refrigerator through fall and winter, and then, in spring, planted in pots and started indoors or out. For outdoor seed starting in fall or winter, plant the seeds in pots as usual, but spread a thin layer of very fine gravel over the top of each pot so the soil won’t get washed out by rains. Washed, natural-colored (undyed) aquarium gravel works well. Wherever you overwinter the pots—in a cold frame or against the wall of a garage—make a level layer of moist sand. Bury the pots to their rims, keeping them close together. This insulates them from severe cold and prevents them from tipping over and spilling. When seeds germinate, move the pots to a sheltered nursery area.

The third process, “scarification,” means nicking the seed coat with a knife or sandpaper so that life-giving moisture can reach the seed’s embryo. If a seed is big, and I can’t dent it with a fingernail, I give it the knife. A small, sharp, pocketknife blade or a rat-tail file is ideal. Don’t go at it too zealously; you need to remove only a very small slice or section of seed coat. You can also line a jar with a sheet of sandpaper cut to fit, screw on the lid, and shake the jar like a maraca until the seed coats are abraded. Scarify seeds just before planting. Seeds nicked too long before planting may dry out and be worthless when they finally reach the soil.

It’s easy to care for seeds planted in pots

I plant most of my seeds—especially slow-growing perennials and annuals— in pots. It’s easier to care for the seedlings and there’s no weeding. You can identify a slow-starting plant by checking the seed packet. If it advises starting the seeds indoors 8 to 10 weeks before the last frost date, you have a slow starter.

Traditional advice is to plant seeds thickly in a flat or tray, then “prick out” individual seedlings for repotting into larger containers. But I prefer to start just a few seeds in 2¼-inch or larger pots, eliminating the need for transplanting altogether. I thin the emerging seedlings with scissors or just plant the whole cluster in the garden.

Soilless mixes help prevent seedling disease

I use a commercial “soilless” seed-starting mix—a blend of milled sphagnum moss, vermiculite, and other sterilized components—so I rarely have trouble with damping-off disease, a fungal problem that causes seedlings to wither and die. To prepare for planting, I pour all but a small portion of the mix into a large bowl and moisten it thoroughly with warm water. Next I fill the containers—plastic pots saved from my periodic nursery buying sprees—to ½ inch below the rim and gently pack the medium to eliminate air pockets. Containers recycled from previous uses should be first sterilized by soaking in a solution of one part bleach and nine parts water.

When the pots are ready, I snip off a corner of the seed packet (or its interior glassine envelope of seeds) and carefully shake three or four seeds into each pot, allowing at least ½ inch between each of them. The tiniest seeds can slide out too quickly so, for better control, I fold a small piece of stiff white paper in half, pour the seeds into the strip, and dole them out by lightly tapping the paper strip. If the seeds are large enough to easily see, I use my fingertip (making sure it’s dry so seeds don’t adhere to it) to push each seed gently against the moist, soilless mix, so it makes good contact. Instead of burying the seeds, I use a sieve to cover them with a thin layer of the reserved seed-starting mix. If the seeds require light to germinate, I don’t cover them at all. I then make a label with the plant’s name and date, and push the marker into the pot so that it doesn’t protrude above the rim.

If I expect the seeds to germinate within a few days or weeks, I cover the pots with a sheet of plastic wrap, glass, or clear plastic to preserve moisture, and check daily. When sprouts appear, I remove the covering. I start a lot of seeds, and don’t worry about providing them with bottom heat to speed germination—I just try to keep things simple. If the seeds are likely to take a long time to germinate—some stratified seeds may spend months in a pot before sprouting—I don’t bother covering them and just take care to keep the soil moist.

Once the pots are planted, I set them on a cookie sheet or other shallow tray for easy transport to a cold frame or other seed-starting area. The trays also make bottom watering easier. It’s important to keep the seed-starting medium moist to speed germination; I use a very fine mist to water the pots from above, or pour water into the tray and let the pots soak it up from the bottom.

Young sprouts need light and a little fertilizer

Since seedlings need light, I place trays of pots on south- or east-facing windowsills. I’ve started as many as 800 pots of seedlings in a season, so windowsill space can be gone before all the pots are placed. If that happens, I move to the basement, or anywhere else indoors, and rig shop lights with fluorescent tubes. Some books recommend tubes that emit specific kinds of light, but standard inexpensive fluorescent tubes also work well. To keep the light source close to the seedlings, I mount the lights on chains so they can be easily moved up or down. Seedlings need 12 to 16 hours of artificial light daily. As for temperatures, room temperatures in the mid-60s are adequate for young seedlings. Warmer temperatures would be fine too. If I’ve sown the seeds in pots outdoors in or out of a cold frame, I don’t worry about providing additional light or fret about the temperature.

After seedlings emerge, I use a water-soluble fertilizer weekly to encourage growth. Fish emulsion or any type of fertilizer will work, but I use Peters or Miracle Gro. If the label doesn’t recommend a strength for seedlings, I mix at the ratio recommended for container plants. If the directions specify “outdoor plants” or “indoor plants,” I follow the recommendations for indoor plants. If there is only a recommendation for outdoor use, I cut the amount of fertilizer in half. For my fertilizers of choice, that is about 1 teaspoon per gallon of water.

Toughen up seedlings, then plant them in the garden

As soon as the seedlings have two or three pairs of true leaves, they’re ready to go out to the garden. But before pampered seedlings go out into the big, wide world, they need toughening up. The aim is to gradually acclimatize plants raised indoors to the rigors of outdoor life. Without this step, known as “hardening off,” tender plant tissues may be damaged by the unaccustomed stresses of sun, wind, and weather.

Begin by moving the seedlings outside to a shady spot protected from the wind and leaving them there for no longer than a couple of hours on the first day. Gradually lengthen their outdoor stays and move the plants into a sunnier spot, if that’s the exposure that they will eventually be planted in. After a week or so, the plants should be ready to go in the ground. A drizzly, gray day is perfect for transplanting—plants will be protected from the desiccating effect of the sun and the moisture will help them settle in quickly. If the weather won’t cooperate, plant late in the afternoon so seedlings get their start in the cool of the evening.

Water your plants well before transplanting them, and water the garden soil until it’s well-moistened but not sopping wet. Slide the plants out of their pots and into place, firm the soil around each with your fingers, and water with a fine mist. Be sure to keep the soil moist until the plants start growing well.