How to Start Seeds Indoors

Growing some of our own food is an obvious way to save money on groceries, but seedlings sold at garden centers can actually get pretty pricey. Starting plants from seed instead is the best way to get as much bang for your gardening buck as possible. An added benefit is that you get to choose the specific varieties of vegetables you want to grow—many of which are not available in garden centers at all. Despite these benefits, starting seed can seem intimidating—something reserved for gardening masters. Actually, starting seeds is fun and empowering. Use these seven simple steps to achieve seed-starting success.

Step 1: Order Seeds

Peruse seed catalogs or the websites of seed companies to find the plants you plan to grow this spring and summer (find a list of our favorite organic and heirloom seed companies in Green Your Thumb with Heirloom Seed Companies). Order seeds now, and sort them according to when they need to be planted. If they will be direct-sown (planted directly in your garden), set those aside. For those that need to be started indoors before being transplanted into the garden as seedlings, sort them according to how many weeks before the last frost they need to be started. Seed packets usually say something like “Start four to six weeks before last frost date.” Hold on to your seed packets. They contain important growing information that you will use later.

Step 2: Figure Out Your Transplant Dates

Next you need to figure out when your last chance of a spring frost will have passed. This is known as the “last frost date.” Your list of planting times will all be back-timed from this date. The best source for this information is The National Climatic Data Center (visit NOAA for frost/freeze date charts), which takes into account yearly changes from factors such as climate change.

You will start most spring seedlings four to six weeks before the recommended transplanting date, including tomatoes, sweet peppers, eggplants, broccoli, cabbage, kale and collards. Onions, hot peppers and celery need more time to get established, eight to 10 weeks. Don’t start your seeds indoors too soon: If the seedlings get very large, they’ll suffer more damage when you move them outside.

Step 3: Plant Seeds

You can grow healthy, sturdy seedlings in a sunny window, but rotate your plants every few days so they don’t lean toward the window and become leggy. Fluorescent lights can help seedlings get enough light, but turn the lights off at night to give the growing plants a rest. You can also start seeds outdoors in the protection of a cold frame or greenhouse if you have one.

Start your seeds in a good, organic seed-starting mix from a local store or make your own soil mix. Purchased mixes are sterile, light and hold moisture well. Use a large container to mix water into your soil mixture until it’s moist, but not soggy. Fill nursery flats, small pots or other containers nearly to the top with your seed-starting mix. The best container sizes are 2 to 3 inches deep and at least 3 inches wide. Make sure your containers have drainage holes.

Use your finger or a chopstick to make holes in the soil for the seeds. The holes can be close together because you’ll move your plants into larger containers before they’re very big. For large seeds, make holes about 1⁄2-inch deep. For smaller seeds, 1⁄8- to 1⁄4-inch deep is plenty. Place one to three seeds in each spot. (It’s good to sow extra because not all of your seeds will come up. Pull out any extras once they sprout, or very gently move them to an empty spot.) Cover the seeds with fine soil and gently press down. If you added enough water when you mixed the soil, you won’t need to water again for at least a day.

Make sure to clearly label all of your seedlings so you can keep track of which varieties you end up liking best.

Step 4: Watch Your Seedlings Grow

Water gently and sparingly, enough to keep the soil moist but not soggy. It may be several days or even a couple of weeks before you see your first seedlings break through the soil. It’s important not to water too much during this time or your seeds could rot. Make sure your seedlings always have plenty of light, moisture and overhead space to grow.

The first leaves you see are called the “seedling leaves” or cotyledons. Most garden plants have two seedling leaves that open up at the same time, but corn and other grasses only have one. Your plants will start growing larger, “true” leaves after the seedling leaves appear.

Step 5: Pot Up

When your seedlings have two to three true leaves, it’s time to move them into larger flats or pots (this is called potting up). Don’t give them too much room too quickly: Seedlings grow best and are easier to keep evenly moist if you move them to slightly larger containers rather than enormous ones.

Now is a good time to make sure your plants are getting the nutrients they need to keep growing until it’s time to move them to the garden. Do this by potting them up into fine, fertile compost. You could use a mix of compost and soil or a purchased potting mix. Moisten your potting soil first and fill the container nearly to the top. Use a narrow trowel or stick to make a deep hole. While holding the soil aside, slide in the seedling. It’s best if the seedling roots are a bit spread out and generally point downward. Gently press down on the soil around the base of the plant, avoiding mounding soil against the stem. Give each plant a bit more water, and you’re done.

Step 6: Harden Off

A couple of weeks before you expect to transplant seedlings into your garden (see Step 2), begin “hardening off” your plants by moving them to a cold frame or setting them outside for several hours each day and bringing them back inside at night. This way, they will gain exposure to the elements, which will make them stronger.

Step 7: Set Plants Out

Transplant seedlings into your garden, paying attention to the depth and spacing requirements given on the original seed packets. This information is usually also available on seed company websites if you didn’t keep the packets.

When to Start Seeds Indoors

* usually sown directly in garden soil, but may be started early indoors

Chart adapted from one of our most highly recommended garden seed companies, Johnny’s Selected Seeds.

This article is adapted from Southern Exposure Seed Exchange, one of our most highly recommended seed companies. Order heirloom and organic seeds from Southern Exposure.