Indoor Seed Starting

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It's possible to have a fine vegetable garden by buying young plants. But you will have a much wider range of possibilities if you start your own plants from seeds indoors.

Not only is it much cheaper, but you can buy seeds for many more varieties than you will find for sale as plants. That will allow you to experiment with more different flavors, shapes and colors, and to harvest your favorite edibles over a longer period by planting varieties that mature at different times. Why is it necessary to start plants before it's warm outdoors? Well, for some species, it's not (see this article on direct-sowing seeds).

But many of our favorite flowers and vegetables, including tomatoes, peppers, squash and beans, evolved in places such as Central America and Mexico where they had many more hours of sunlight in their growing season that they can get in most of the United States. Their seeds will not sprout in soil that is still cold in spring and the fruits need more sun to ripen than is available in the waning days of autumn.

If you were to sow tomato seeds in the ground outdoors in May in New England, Oklahoma or Minnesota, the plants would take so long to grow that the first frost in October would likely kill them before you got a single ripe tomato.

Even for crops that don't come from near the equator, starting seeds indoors gives plants a head start that brings earlier harvests and greater yield.

The same is true for many of our favorite annual flowers. If you start them indoors, they can spend more time in your garden flowering instead of getting mature enough to flower. Even many perennials benefit from a good head start indoors.

For your first experience of starting seeds, it's wise not to take on too much. Start a couple of dozen plants in three or four varieties while you learn how it all works.

Different plants have different needs, so consult the seed packet to find out how many weeks each variety will take to get ready indoors before your last frost date.

Many vegetable seed packets state a number of days to maturity, such as "65 days" or "80 days." Make sure you know whether that means days from sowing the seed or days from transplanting outdoors; it varies from vegetable to vegetable.

Starting seeds is not complicated or difficult, if you understand the process. The basic ingredients are a proper growing medium, containers, light, warmth, water and attention.

Growing medium

Seedlings are very delicate. For the best chance of success, start them in a fresh, sterile seed-starting mix that is light and fluffy to hold just enough moisture. If the growing medium is too wet or not sterile, disease can strike. If it is too heavy or sticky, fine new roots won't be able to push through it.

You can use bagged seed-starting mix, or buy compressed pellets of peat or coir (coconut husk fibers) that expand when wet. Since seeds contain the nutrients the seedlings will need, fertilizer isn't important in your seed-starting mix.

The Right Container

Anything that will hold the growing medium will work. You can use cell-packs or pots from last year's annuals, yogurt cups or other found containers. But you must clean them and sterilize them in a solution of 1 part bleach to 9 parts water. Make sure they have good drainage holes so excess water can drain away. And get a shallow waterproof tray that will hold them.

There's no point in using containers more than 3 to 4 inches across, since you will be transplanting the young plants to the garden (or container garden).

Another alternative is pots that break down in the soil. You can plant them right in the garden and avoid disturbing the young plant's roots. Some are shaped from compressed peat or coir, or you can make your own from newspaper. Don't confuse these with biodegradable resin pots; those will break down in a landfill or, eventually, in a compost heap, but you can't plant them in the garden.

Seed-starting kits are readily available and can be a big help. They usually include an attached set of good-sized containers, a tray to set them on and a clear lid to hold in humidity during the early stages.

Large-scale gardeners often do a two-step: They closely sow seeds in a shallow tray until they sprout, or "germinate." Then they gently prick the small sprouts out and transplant them to larger containers. This saves germination space if you are starting seeds in large numbers, but it isn't necessary. A beginner starting a modest number of seeds can germinate them right in the containers in which they will grow to transplant size.

How Much Light?

Seedlings need lots of light or they will be stalky, spindly and feeble. A very sunny, south-facing window may do for a handful of plants if you are not too far north. But most gardeners use artificial lights so they can raise more plants and make sure they get enough rays.

You can buy specially-made plant light setups for anywhere from $80 to $500, depending on complexity and capacity. But many gardeners do just fine with inexpensive T-12 or T-8 fluorescent shop lights from the home improvement store.

To provide a wider spectrum of light, use one cool-white tube and one red-light tube in a two-tube fixture. Newer-fangled T-5 tubes deliver more light from a single tube but are more expensive and require a special fixture.

The crucial thing is to rig the light fixture so you can raise it. You must keep the lights just 3 to 4 inches above the plants as they grow. That's why incandescent light bulbs won't work; if they are close enough to give a plant a useful amount of light, their heat will destroy it. Fluorescent bulbs give more light but stay cool.

Most often, a shop light is hung from open-link chains with S-hooks. As the plants grow, the light can be lifted link by link so it stays right above the plants. You can hang the light from a basement ceiling, from a home-made lumber frame or even under a table, with the plants on the floor.

A lamp timer will take over the chore of turning the lights on and off so the plants get 16 to 18 hours of light every day and a good rest at night.

How Much Warmth Do Seeds Need?

Seed-starting happens in two stages: germination and growing. Germination is the sprouting stage, when the embryo of the plant emerges from the seed. You won't need light at this stage, but you will need gentle warmth (not harsh heat). Provide it by setting the containers on top of a refrigerator or dryer; by propping them a few inches above (not on) a radiator; or by using special heating mats sold for the purpose.

Once you see green sprouts about half an inch tall, you will move your plants under the lights in a cooler environment--about comfortable room temperature, between 60 and 70 degrees. A cold garage won't do; neither will a broiling furnace room.

How Much Water Do Seeds Need?

Plants consist mostly of water and they need it for the photosynthesis that gives them energy to grow.

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Check out our Seed Starting Kits & Mixes

Sow the seeds in moistened mix. Cover the containers to hold in humidity while the seeds germinate--with the cover from your kit, or with a loosely fastened plastic bag. Once they sprout, uncover the containers and water them from the bottom, by pouring water into the tray. Never water the seed-starting mix from the top; that courts disease (especially a fungus disease called "damping off") and may dislodge or damage the sprouts. Make sure air circulates freely so humidity isn't trapped around plants.

So-called "self watering" seed-starting kits are helpful in keeping the water supply steady. In these arrangements, the containers sit on a fiber mat that wicks just enough moisture from a reservoir. These kits aren't magic, though; you still have to keep that reservoir filled with water.

How Often Should I Check My Seeds?

This is the secret ingredient to successful seed-starting. You'll need to check daily: To see if the seeds have sprouted; to remove the cover when it's time and move the sprouts under lights; to make sure they stay properly moist; to keep a self-watering reservoir full; to raise the lights so they stay just the right distance above the plants; and to make sure the lights and timer haven't malfunctioned. If you are starting a few seeds on the windowsill, turn the plants every day so they don't bend toward the light.

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As you plan your seed starting, factor in your convenience and habits. Will you really remember to check seeds in the basement daily? It might be wiser to start seeds in the guest room or kitchen where they will be handier, even if you have space for fewer seedlings.

As your seedlings grow, watch the weather. Although a few crops can go outside earlier (read the seed packet), most should stay indoors until after the last frost date for your area has passed and your soil has warmed. If your area is having a cold spring, hold off.

Gardeners are always eager, but many a carefully nurtured tomato seedling has been killed by a May frost or simply slowed down by cold soil. Protect your investment of time and attention by planting later rather than earlier.

Then introduce your plants to the outdoors gradually, a process called "hardening off." For a few hours one fine spring day, then a few hours more the next, give your plants a taste of the outdoors, but bring them in at night. After a week or so, they will have acclimated to the outdoors and will be ready to transplant.