Everything You Need To Know About Starting Seeds Indoors

It’s surprisingly simple—and you’ll get your veggies and flowers way earlier!

February 9, 2017
starting seeds on kitchen counter
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Starting seeds indoors will give you earlier vegetables and flowers. And because you’re not at the mercy of planting only what the garden center has to offer, your cultivar choices will be endless. Feeling apprehensive? It’s normal for a seed-starting newbie. But rest assured, the act of seed planting is quite simple. 

First, select your work area—a surface at a comfortable height and close to a water supply where you’ll have room to spread things out. Next, gather your supplies: seed-starting containers, starting medium or soil mix, watering can, labels, marking pen, and seed packets. Finally, follow this simple step-by-step guide and you’ll be presiding over a healthy crop of seedlings before you know it. 

(Whether you're starting your first garden or switching to organic, Rodale’s Basic Organic Gardening has all the answers and advice you need—get your copy today!)

biodegradable seed containers
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Choose Your Containers

You can use 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, making the process easier. Other pots must be slipped off the root ball before planting.

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 online suppliers. You can also build your own wooden flats.

You can also 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. You can also make DIY newspaper pots—check out this tutorial for the details.

soil in hands
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Select The Right Soil 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 hardens into a dense mass that delicate young roots can’t penetrate. Instead, 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

Moisten the planting mix with warm water before you fill your containers, especially if it contains peat moss or milled sphagnum moss. Let your seedlings grow in the mixture until they develop their first true leaves, and then transplant into a moist, 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. 

Some gardeners prefer to plant seeds directly in potting mix and eliminate transplanting. This makes sense for plants such as squash and melons that won’t grow well if they’re roots are disturbed, and that grow best in large individual pots.

If you’re sowing directly in flats, first line the bottom with a sheet of newspaper to keep soil from washing out. Scoop pre-moistened 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.

Related: 5 Ways You Can Improve Your Soil

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Sow Your Seeds

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. (Try this great soil recipe for window boxes.) 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.

Be sure to 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. Then, 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. (Check out these 9 mistakes you're making every time you water your garden.)

Cover the containers, 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. Check the flats daily; keep the soil moist but not waterlogged. As soon as you notice sprouts nudging above the soil surface, expose the flat to light.

Related: 5 Reasons You Should Start Your Own Seeds Instead Of Buying Seedlings

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Your Seed Sowing Timetable

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

Related: How To Get 90 Pounds Of Tomatoes From 5 Plants