Seed-Starting Chart: Getting Ready For The Spring
You can start seeds in almost any kind of container that will hold 1 to 2 inches of starting medium and won’t become easily waterlogged. Once seedlings form more roots and develop their true leaves, though, they grow best in containers that provide more space for root growth and have holes for drainage.
You can start seedlings in open flats, in individual sections of a market pack, or in pots. Individual containers are preferable, because the less you disturb tender roots, the better. Some containers, such as peat pots, paper pots, and soil blocks, go right into the garden with the plant during transplanting. Other pots must be slipped off the root ball before planting.
Square or rectangular containers make better use of space and provide more root area than round ones do. However, individual containers dry out faster than open flats. Many gardeners start seeds in open flats and transplant seedlings to individual containers after the first true leaves unfold. Choose flats and containers to match the number and types of plants you wish to grow and the space you have available.
Excellent seed-starting systems are available from garden centers and mail-order suppliers. You can also build your own wooden flats. If you raise large numbers of seedlings, it’s useful to have interchangeable, standard-sized flats and inserts.
You can reuse your seedling containers for many years. To prevent problems with dampening off, you may want to sanitize flats at the end of the season by dipping them in a 10 percent solution of household bleach (1 cup of bleach plus 9 cups of water).
You can recycle milk cartons and many types of plastic containers as seed-starting pots. Just be sure to poke a drainage hole in the bottom of each. Cut lengths of clothes hanger as a frame for your flats so you can wrap them in plastic to encourage germination. You can bend the wire to fit into a plastic flat filled with pots or six-packs, or staple the wire to the sides of a wooden flat as shown at right. Use clear plastic wrap or plastic bags (like the ones from the dry cleaner) to enclose the flat.
Two make-at-home seed-starting containers are newspaper pots and soil blocks. To make pots from newspaper, begin by cutting bands of newspaper about twice as wide as the desired height of a pot (about 4 inches wide for a 2-inch-high pot). Wrap a band around the lower half of a jar a few times, and secure it with masking tape. Then form the bottom of the pot by creasing and folding the paper in around the bottom of the jar. You can also put a piece of tape across the pot bottom to hold it more securely in place. Slip the newspaper pot off the jar. Set your pots in high-sided trays with their sides touching. When you fill them with potting mix, they will support one another. There are also commercial molds for making newspaper pots.
Seed-Starting + Potting Mixes
Seeds contain enough nutrients to nourish themselves through sprouting, so a seed-starting mix does not have to contain nutrients. It should be free of weed seeds and toxic substances, hold moisture well, and provide plenty of air spaces. Don’t use plain garden soil to start seedlings; it 536hardens into a dense mass that delicate young roots can’t penetrate.
Make your own seed-starting mix by combining one part vermiculite or perlite with one part peat moss, milled sphagnum moss, coir, or well-screened compost. Or, buy bagged seed-starting mix. Let your seedlings grow in such a mixture until they develop their first true leaves, and then transplant into a nutrient-rich potting mix (be sure the mix you choose is labeled organic, or check the list of ingredients, and avoid mixes that contain added synthetic fertilizer). To make your own potting mix, combine equal parts compost and vermiculite. For more recipes for mixes, see the Houseplants entry. For safe handling instructions for seed-starting and potting mixes, see the Container Gardening entry.
Some gardeners prefer to plant seeds directly in potting mix and eliminate transplanting. Planting in large individual pots is ideal for plants such as squash and melons that won’t grow well if their roots are disturbed.
Moisten the planting mix before you fill your containers, especially if it contains peat moss or milled sphagnum moss. Use warm water, and allow the mix time to absorb it. When you squeeze a handful of mix it should hold together and feel moist, but it shouldn’t drip.
If you’re sowing directly in flats, first line the bottom with a sheet of newspaper to keep soil from washing out. Scoop premoistened planting medium into the containers or flats, and spread it out. Tap the filled container on your work surface to settle the medium, and smooth the surface with your hand. Don’t pack it down tightly.
Soil blocks encourage well-branched roots and produce good seedlings. You can buy molds to make soil blocks, but making them is a messy, labor-intensive process.
Begin by mixing a wheelbarrow-load of potting soil. Use plenty of peat moss and lots of water to make a thick, wet, gummy mass with the texture of peanut butter. Jam the soil-block mold into the block mix. Press the mold hard against the bottom of the wheelbarrow, and then lift and eject the blocks from the mold onto a tray. Then arrange the blocks in flats and plant directly into them. Don’t let soil blocks dry out: Because of their high peat content, they don’t absorb moisture well once they have become dry. Water from the bottom or mist gently until roots grow. Once roots fill the blocks, they become solid and easy to handle.
Space large seeds at least 1 inch apart, planting 2 or 3 seeds in each pot (snip off the weaker seedlings later). Plant medium-sized seeds ½ to 1 inch apart, and tiny ones about ½ inch apart. If you’re sowing only a few seeds, use your fingertips or tweezers to place them precisely. To sprinkle seeds evenly, try one of these methods:
- Take a pinch of seeds between your thumb and forefinger and slowly rotate thumb against finger—try to release the seeds gradually while moving your hand over the container.
- Scatter seeds from a spoon.
- Sow seeds directly from the corner of the packet by tapping the packet gently to make the seeds drop out one by one.
- Mix fine seeds with dry sand, and scatter the mixture from a saltshaker.
To sow seeds in tiny furrows or rows, just make shallow ¼- to ½-inch-deep depressions in the soil with a plant label or an old pencil. Space the seeds along the bottom of the furrow.
Cover the seeds to a depth of three times their thickness by carefully sprinkling them with light, dry potting soil or seed-starting medium. Don’t cover seeds that need light to germinate (check the seed packet for special germination requirements). Instead, gently pat the surface of the mix so the seeds and mix have good contact.
Write a label for each kind of seed you plant and put it in the flat or pot as soon as the seeds are planted, before any mix-ups occur.
Set the flats or pots in shallow containers of water and let them soak until the surface of the planting medium looks moist. Or you can gently mist the mix. If you water from the top, use a watering can with a rose nozzle to get a gentle stream that won’t wash the seeds out of place.
Cover the container, using clear plastic or a floating row cover for seeds that need light, or black plastic, damp newspaper, or burlap for those that prefer the dark.
Finally, put the containers of planted seeds in a warm place where you can check them daily. Unless the seeds need light to germinate, you can save space the first few days by stacking flats. Just be sure the bottom of a flat doesn’t actually rest on the planting mix of the flat below. Check the flats daily; unstack as soon as the seeds start to sprout. Keep the soil moist but not waterlogged. As soon as you notice sprouts nudging above the soil surface, expose the flat to light.
To plan the best time to start seedlings indoors in spring, you need to know the approximate date of the average last spring frost in your area. Count back from that date the number of weeks indicated below to determine the appropriate starting date for various crops. An asterisk (*) indicates a cold-hardy plant that can be set out 4 to 6 weeks before the last frost.
- 12 to 14 weeks: onions*, leeks*, chives*, pansies*, impatiens, and coleus
- 8 to 12 weeks: peppers, lettuce*, cabbage-family crops*, petunias, snapdragons*, alyssum*, and other hardy annual flowers
- 6 to 8 weeks: eggplants, tomatoes
- 5 to 6 weeks: zinnias, cockscombs (Celosia spp.), marigolds, other tender annuals
- 2 to 4 weeks: cucumbers, melons, okra, pumpkins, squash