A Gardener's Guide to Starting Seeds Indoors

You can sow (plant) the seeds of most fruit and vegetable plants directly into your garden. It's the most affordable, convenient path to a bounty of fresh, delicious produce from your own backyard. So why would anyone want to buy costly seedlings (starter plants) from a nursery or sow seeds indoors instead of outdoors?

Put simply, you cannot put every plant or seed directly into the soil because the growing period of some plants is longer than the growing season of your hardiness zone. Therefore, some plants need to be grown indoors (or at a nursery) before you can transplant them into the garden. Starting your own seeds indoors is more economical and will give you a head-start on the growing season. Plus, you'll be able to experiment with a wider variety of plant species than the common varieties of seedlings available at your local nursery.

You should always consult the back of your seed packets for exact planting instructions, but here are some examples of plants that typically need a head start indoors (including the number of weeks prior to your zone's last anticipated frost date that you should start the seeds indoors): Starting Your Seeds Indoors
There are 10 simple steps to follow to start or "germinate" your seeds indoors. If you buy seedlings from a nursery, skip to step 8 below.

1. Choose a location. The best place to germinate your seeds is an area away from the everyday traffic (and pets) that's also warm, full of light, and free from drafts. Basements, shelves, and sun porches usually make suitable locations.

2. Gather your trays. Seed starting mixtures and trays are also widely available at nurseries and home improvement stores, but you can also make your own trays out of egg cartons, yogurt tubs or other "recycled" containers. Whatever you use, it's a good idea to sterilize your trays, especially if you are reusing them, and to use trays with adequate drainage holes at the bottom.

3. Plant your seeds. Fill your trays or containers about 2/3 full with your starter mix (or loose, fertile, and disease-free soil) and pat it down until it is level but still loose. Each type of seed has a different sowing depth so consult your seed packets for further instructions. A general rule of thumb is to plant seeds twice as deep as they are wide. Place several seeds in each container, but don't scatter too many as overcrowding will inhibit proper growth. Don't forget to label what you are growing, especially if you have multiple trays of different seeds growing simultaneously.

4. Provide adequate lighting. To sprout, seeds need 12-16 hours of light, so growing them under a fluorescent light is ideal. A windowsill is not an option even in the sunniest spot in your home, as late summer or early spring has unpredictable light at best—and usually not 12-plus hours' worth. Most gardeners agree that a 40-watt fluorescent light works well.

5. Control the temperature and humidity. Make sure the room temperature is regulated as well, ideally between 65 degrees and 70 degrees Fahrenheit for most seeds (consult your seed packet for specific instructions). An easy way to boost the temperature is to place a humidity dome over the plants or a heated mat under the plant trays. Make sure to maintain adequate moisture levels; soil should be damp, but not drenched. No fertilization is required during the germination period. If you are using any artificial heat, remove it when after the seeds sprout their first leaves.

6. Start thinning. Once your tiny plants start to sprout, it's time to show some tough love. Thinning might seem like a waste of a healthy plant, but it is a necessary step to help your seedlings become strong and healthy. To thin, clip the weaker sprouts at the soil level, as pulling them out can damage the delicate root systems. At this point, give the seedlings a half-strength fertilizer that is specific for houseplants about every two weeks.

7. Upgrade your containers. When several inches high, it's time to carefully transplant your seedlings into bigger containers. Try using some peat pots, as they are biodegradable and can be planted straight into the garden when outdoor conditions are appropriate.

8. Acclimate your plants to the outdoors. The final step is to transition your plants into the garden, a process called “hardening off.” After the threat of frost has passed, take your little seedlings outside for about an hour, in an area that is sheltered from the sun and wind. Gradually increase this time and exposure to the outdoors over a two-week period until, finally, your little plants are ready to be planted into the garden—ideally on an overcast day. (If you purchased seedlings from a store, ask the seller whether or not they were hardened off, though assume so if the plants were outside when you bought them.) 

9. Transplant your plants into the garden. Whether you are planting seeds directly into the soil or transplanting seedlings, consult your seed packet for sowing depth and spacing. (or, as a general rule, dig a hole that is twice as wide and deep as your transplants). Handle your seedlings carefully because, essentially, they are delicate babies.

10. Care for your new plants! Seedlings and directly-sown seeds require TLC once they are in the garden. Watering them regularly is important as they are in their infancy and not yet "established." Protect them from wind and predators (birds are notoriously munch on freshly planted seeds). Mulching around plants, once established, is a helpful way to increase moisture retention, too.