Indoor Seed Starting

Indoor Seed Starting

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. This 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 some plants before it's warm outdoors? Many of our favorite flowers and vegetables, including tomatoes, peppers, squash and beans, are native to such places as Central America and Mexico, where they had many more hours of sunlight in their growing season, and a much longer season of warm temperatures than they can get in most of the United States. Their seeds will not sprout in soil that is still cool 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 some 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 maturing enough to flower. Even many perennials benefit from a good head start indoors.

Note that not all plants should be started indoors, some are best sown directly in the garden (see this article on direct-sowing seeds). Different plants have different needs, so always refer to the directions on the seed packet to tell you when and how to sow your seeds.

For your first experience of starting seeds, it's wise not to take on too much. Start no more than a couple of dozen plants in three or four varieties while you learn how it all works. 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 your attention.

Seed Starting Introduction

Finding the Right 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 and designed 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.

Burpee offers a range of seed starting soils, from compressed coir pellets (coconut husk fibers) that expand when wet, to bags of loose seed starting formula. All our mixes have a trace of starter fertilizer in them so you will not need to start fertilizing until the seedlings have several sets of leaves.

Choosing the Right Container for Indoor Sowing

Gardening ContainerAnything that will hold the growing medium and has drainage holes will work, but we recommend specially designed seed starting kits because they include everything you need to grow strong, healthy seedlings. Burpee offers a variety of seed starting kits that include trays with cells, expandable coir pellets, a tray to set them on and a clear lid to hold in humidity during the early stages.

An alternative to using the kits is to purchase biodegradable pots that break down in the soil. You can plant them right in the garden and so avoid disturbing the young plant's roots. Some are shaped from organic wood fiber or peat, 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 directly in the garden. Burpee offers a range of fiber pots and a kit for making pots from newspaper.

How Much Light?

Seedlings need lots of light or they will be spindly and feeble. A very sunny, south-facing window may do just the thing for a handful of plants if you are not too far north, but artificial plant lights can ensure that your plants will get the light they need even on cloudy days and during those shorter winter days. Burpee offers a range of lighting options for gardening from platinum LED lights that you mount from the ceiling to light carts with LED or T-8 light bulbs, to our smallest tabletop Ultimate Grow Light with CFL bulb. All these lights have the broad spectrum range of light rays needed by plants. They are adjustable in height so you can raise them as your seedlings grow.

A timer can be helpful to turn the lights on and off so the plants get the 16 hours of light they need every day, and a good rest at night. You want to keep the lights just 3 to 4 inches above the plants.

How Much Warmth Do Seeds Need?

Seed-starting happens in two stages: germination and growing. Germination is the sprouting stage, when the root and leaves emerge from the seed. You won't need light at this stage because it occurs under the soil, but you will need gentle warmth (not harsh heat). You can provide heat by using special heat mats available from Burpee in a range of sizes to fit your seed starting needs. These will keep your seedlings about 10 degrees F warmer than the air temperature, allowing the seeds to germinate faster, leading to healthier seedlings. Once you see green sprouts about half an inch tall, you need the plant lights. You can remove the heat mats as long as the room temperature is between 60 and 70 degrees F.

How Much Water Do Seeds Need?

Garden wateringPlants consist mostly of water to keep them turgid, and they need it for the photosynthesis that gives them energy to grow. Water is also what starts the germination process. But while water is essential for plant growth, overwatering is the most common cause of seedling failure.

Sow your seeds in an evenly pre-moistened mix. It should be moist but not soaking wet. Cover the container to hold in humidity while the seeds germinate with the cover from your kit, or a clear plastic wrap. Try to allow for some air circulation, however. Burpee’s seed starting kit lids are designed to fit loosely on the top of the try to ensure some air circulation.

Once they sprout, uncover the containers and water them from the bottom by pouring water into the tray. Make sure air circulates freely so humidity isn't trapped around plants.

How Often Should I Check My Indoor Seeds?

This is the secret ingredient to successful seed-starting: you should check your seeds daily. Check to see if the seeds have sprouted so you can remove the cover when it's time and make sure the seedlings have light; check to make sure they stay properly moist but not too wet; check your reservoir if you have a self-watering kit; check the seedlings’ growth and raise the lights so they stay 3-4” above the plants; and check 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.

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 (refer to 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.

Finally, introduce your plants to the sun gradually, a process called "hardening off". Expose them to sunlight for one hour more each day for a week. During this time bring them to a protected location outside when they are not in the sunlight. If there will be a frost at night, bring them inside. After a week or so, they will have acclimated to the outdoors and will be ready to transplant.

May 21, 2021