For seed-starting success, follow this simple plan.
1. Choose a fine medium.
For healthy seedlings, you’ve got to give them a loose, well-drained medium (seed-starting mix) composed of very fine particles. You can buy a seed-starting mix at your local garden center—or make your own. Don’t use potting soil—often, it’s too rich and doesn’t drain well enough for seedlings.
2. Assemble your containers.
Many gardeners start their seeds in leftover plastic “six packs” from the garden center, empty milk cartons, or Styrofoam cups. If you don’t have containers on hand, you can buy plastic “cell packs,” individual plastic pots, or sphagnum peat pots. Or make your own pots from newspaper. Whatever you use, be sure your containers drain well (usually through holes in the bottoms of the containers).
Set the pots inside a tray so that you can water your seedlings from the bottom (by adding water to the tray) rather than disturbing them by watering from the top. You can buy seed-starting trays at garden centers and many hardware stores.
3. Start your seeds!
Moisten your seed-starting mix before you plant your seeds. If you water after you plant the seeds, they can easily float to the edges of the container—not where you want them to be. To moisten the mix, simply pour some into a bucket, add warm water, and stir. After about 8 hours (or when the mix has absorbed the water), fill your containers with the moistened mix.
Plant at least two, but no more than three, seeds per container. The seed packet usually tells you how deep to plant, but a good rule of thumb is three times as deep as the seeds’ smallest diameter. (Some flower seeds require light to sprout—if that’s the case, simply lay the seeds on the surface of the mix, then tamp them in gently with your finger.)
After you’ve planted your seeds, cover the tray loosely with plastic to create a humid environment. At 65° to 70°F, your seeds should sprout just fine without any supplementary heat. If the room temperature is cooler than that, you can keep the seeds warm by setting the tray on top of a heating mat made specifically for starting seeds.
Tomato, zucchini, and pumpkin seeds should push their sprouts through the surface of the mix in a few days. Peppers sprout in about a week. And some seeds, such as parsley, can take as long as 3 weeks to sprout, so be patient.
Check your trays daily. As soon as you see sprouts, remove the plastic covers and immediately pop the trays beneath lights. You can invest in grow lights (which provide both “warm” and “cool” light), but many gardeners have good results with standard 4-foot-long fluorescent shop lights. Set your seedlings as close to the light as possible—2 or 3 inches away is about right. When seedlings don’t get enough light, they grow long, weak stems. As the seedlings grow, raise the lights to maintain the proper distance.
And don’t worry about turning off the lights at night. Contrary to popular belief, seedlings don’t require a period of darkness. Fluorescent lights are only one-tenth as bright as sunlight, so your seedlings will actually grow better if you leave them on continuously.
5. Feed and water.
Your seedlings will need a steady supply of water, but the soil shouldn’t be constantly wet. The best method is to keep the containers inside a tray, water from the bottom, and allow the soil inside the containers to “wick up” the water.
If your growing medium contains only vermiculite and peat (as many seed-starting mixes do), you’ll also need to feed your seedlings. When the seedlings get their first “true” leaves (not the tiny ones that first appear, but the two that follow), mix up a fish emulsion solution one-quarter to one-half the recommended strength and add it to the seedlings’ water every other week. As the plants grow bigger, gradually increase the strength of the mixture.
6. Keep the air moving.
Your seedlings need to be big and strong by the time you move them from their cushy indoor surroundings to the harsh realities of the outside world. You can help them grow sturdy, stocky stems with a small fan. As soon as you see those first true leaves, set the fan to blow lightly but steadily on the seedlings, all day long. The air circulation also will minimize their chance of fungal disease while they’re crowded together indoors.
Those well-watered, well-fed, and well-fanned seedlings will soon need more root space. Shortly after the second set of true leaves appears, take a deep breath and thin your seedlings to one per pot. Use small scissors to clip off the weaker plants at the soil line, leaving only the stockiest plant.
Next, carefully “pot up” the survivors into larger, 3-or 4-inch pots. Squeeze the sides of the smaller containers all around, turn them upside down, and the plants should come out easily—soil and all. Immediately set them into the larger containers and fill with a mixture of 3 parts potting soil and 1 part your own screened compost.
(If you started your seeds in peat pots or homemade newspaper pots, you can plant both the seedling and its pot in the larger container; the pot eventually will decompose.)
Plant tomatoes deep in the new container to encourage them to develop a larger root system to support these often top-heavy plants. With most other plants, the soil level in the new pot should be about the same as in the smaller container. After you’ve finished repotting, water the plants well and set them back under the lights.
About a week or two before you plan to transplant your seedlings to the garden, begin taking them outdoors to a protected place, such as inside a coldframe or near a wall, for increasing lengths of time on mild days. This will help them adjust to the conditions outside—a process known as hardening off. Start with just a couple of hours each day, work up to a full day, and then leave them out overnight.
When you finally transplant the seedlings to the garden, be careful not to disturb their roots. Gently pop them out of their containers, keeping as much soil attached to their roots as possible. Again, plant tomatoes deeply, but set other plants at about the same depth as they were in their pots (or just slightly deeper).
9. Seal it with a K.I.S.S.
Most important, relax! Don’t worry if you forget to do something or don’t follow all the “rules.” Except for hardening off, all of these rules are flexible. Before long, you will learn what works best for you—and will have a few secrets of your own to share with fellow seed starters.