How to Start Seeds Indoors

Tips for Producing Healthy Seedlings

Tomato Seedlings

Kevin Summers / Getty Images

You can start your vegetables from young plants, but some gardeners might think it's a better experience to start them from seeds—plus, it's a less-expensive way to grow an expansive vegetable garden.

Certain plants have long growing seasons, so they have to be started indoors before transplanting them outside when the weather warms. Starting seeds indoors requires the same basic elements as growing plants outdoors: seeds, soil, light, water, and food.

2:04

Watch Now: Mistakes to Avoid When Growing Seeds Indoors

  1. Choose Which Seeds to Grow

    It's not always easy to decide what seeds to grow. There are so many choices, and it's tempting to want to try them all. Keep in mind, however, that as your seedlings grow, they will need to be moved into larger pots that will take up even more space, so choose wisely. Certain vegetables, such as root vegetables like carrots and beets, don't like to have their roots disturbed, so it's a better idea to start them outdoors instead of transplanting them.

    Buy seeds of plants you're certain you can't find at local garden centers or plants that you want to grow in large quantities inexpensively. There are dozens of seed catalogs available online. You might want to join forces with other seed starters and arrange a seed swap to grow and trade different varieties.

  2. Start the Seeds at the Right Time

    It's always a bit of a guess to decide when to start seeds. First, you'll need to know when your last expected frost date is. Next, check your seed packet to see how many weeks growth are required before setting outdoors. Count back that many weeks from your last expected frost date to get an approximate date for starting those seeds.

    It's approximate because the weather does not always live up to predictions, but you'll be in the ballpark. Different plants will require different timing, so use a calendar to mark down when to start what.

  3. Pick the Proper Container

    Seeds can be started in a variety of containers, as long as the one you choose is well-draining and clean. Many seed catalogs offer special growing containers for seedlings, but you can also use egg cartons that have holes poked in the bottom to allow water to drain.

    After you plant the seeds, label each type of vegetable and cover the chosen container with clear plastic wrap, which will hold in humidity and help the seeds germinate.

  4. Pot With a Seed-Starting Mix

    Start the seeds in a seed-starting mix—which doesn't contain any actual soil—as it provides a good balance of drainage and water-holding capacity, which creates an ideal condition for sprouting the seeds. Avoid using garden soil, which typically doesn't drain well and may introduce disease spores to the plants.

  5. Provide Warmth for Germination

    Before the seeds turn into seedlings, they need to germinate. This process doesn't need light, but it does need gentle warmth to occur. You can invest in special heat mats, which will lead to faster germination, or you can put the planted seeds in a warm area until you see green sprouts that are a half-inch tall.

  6. Give Seedlings Enough Light

    Seedlings need a lot of light to grow successfully. If possible, start seeds on a south-facing windowsill or in a room that receives a full day of bright light—at least eight hours.

    However, that can be hard to come by in winter, so gardeners may need to supplement their seedling lighting with special plant or grow lights that simulate the full spectrum of the sun. Even then, the lights will need to be left on for 16 to 18 hours per day for your seedlings to grow as strong and healthy as they would in true sunlight.

  7. Water Until Soil Is Moist

    Seedlings need water, but it's easy to give them too much. Overwatering is one of the most common reasons why seedlings don't succeed. Water the seedlings until the soil is moist, but not soaking wet.

  8. Transplant the Seedlings

    After the first set of leaves appear on the seedlings, move them into 3- to 4-inch containers. After transplanting, start feeding the plants with a water-soluble fertilizer at one-fourth of the regular strength. Repeat every week, gradually increasing the concentration. If the seedlings become leggy or spindly, and you're sure they're getting the right amount of light, reduce the concentration of your fertilizer or skip a week.

  9. Watch Out for Pests and Diseases

    Keep your new seedlings healthy and pest-free by keeping a close watch for problems. If you spot an issue, act quickly. Because there are no natural predators indoors for pests like fungus gnats and aphids, disease can spread quickly through tender young seedlings and even onto your houseplants, which may be susceptible to many of the same problems. To prevent problems:

    • Avoid overwatering or allowing plants to sit in water, as this can rot tender roots.
    • Keep a close eye on your plants to be sure they are pest-free. If you see signs of insects, use an herbicide to nip the problem in the bud (keeping the plants away from children and pets to avoid toxicity).
    • Be aware of any issues such as brown spots on leaves, and do your research to determine what the problem is. If you can't resolve the issue, it's best to compost the plant.