How (and When) to Start Seeds Indoors to Prepare Them for Spring Planting

If you've never grown anything from seed, it's easy to write the idea off as difficult or labor-intensive, but that couldn't be further from the truth. Seeds, dormant until placed in soil and given water, hold incredible potential for life when given the right conditions and a little love.

Starting from seed also allows you to choose from far more variety than what's in stock at the local nursery. Paging through seed catalogs and ogling rare varieties might just become your new favorite pastime.

So long as you can commit to keeping the seedbed moist until the seeds germinate, there's a high likelihood you'll find success. You'll have complete control over the quality of raising your plants—among other things, it's important to know exactly how and when to start seeds indoors before beginning the process.

Benefits of Growing From Seed

There are countless reasons to grow from seed. First, starting vegetables, herbs, or flowers from seed is more cost-effective compared to buying young seedlings. The yield is also higher when starting seeds indoors. "A package of seeds can provide so many more plants than you could purchase for the same amount," says Carrie Spoonemore, co-creator of Park Seed's From Seed to Spoon app.

Beyond getting more bang for your buck, growing seeds indoors gives you control over your growing conditions. If you live in a region with oppressive winters, seed starting indoors can help you get a jump start on the gardening season, giving your green thumb an outlet during darker days.

When to Start Seeds Indoors

Timing to start seeds depends on what you're growing and what zone you live in. Your zone will give you the approximate date to plant outdoors in your area. Once you know your growing zone, look at the back of your seed packet to see how many days to germination. "Now, count backwards from the date of planting to determine when to plant," says Spoonemore. "Most plants need at least six weeks from planting to moving outdoors. Some need to be planted as early as January, so check the seed pack to be sure."

Best Container for Starting Seeds Indoors

The container you choose influences factors like moisture, drainage, and root development, which directly impact the growth and health of the seedling. "There are fantastic pre-made seed starting trays that are especially great if you’re new to growing plants from seed," says Ryan McEnaney, garden designer and author of Field Guide to Outside Style: Design and Plant Your Perfect Outdoor Space. "They allow for drainage, the right amount of soil mix, and it’s more obvious how many seeds there are per cell."

There are also biodegradable options, like peat pots, expandable peat or coir pellets, or pots made from composted cow manure, says Spoonemore. You can use individual pots you already have on hand, but many gardeners find it difficult to keep so many larger pots covered, under light, and warm when the seedlings are small, she says.

Best Seeds for Starting Indoors

Many seeds are great to start indoors, but not all need it. "Some will do better starting outdoors as they don’t do well with transplanting or have a shorter germination cycle and are fine starting in the garden," says McEnaney. Some plants that do especially well starting as seeds indoors include:

• Tomato
• Broccoli
• Cabbage
• Eggplant
• Geraniums
• Impatiens
• Dahlia
• Cosmos
• Asters
• Peppers
• Cauliflower
• Lettuce
• Spinach
• Sunflowers
• Petunias
• Marigolds
• Pansies
• Zinnias

How to Start Seeds Indoors

Follow these steps when starting seeds indoors.

1. Prepare Soil and Fill Containers:

Use an organic, soilless seed starting mix when starting seeds indoors (garden soil is too dense and the roots may have a hard time getting through). "Dampen the starting mix by adding water and mixing it thoroughly," says Spoonemore. Damp soil ensures the seeds have access to moisture when they are planted. Fill your chosen containers with the pre-dampened starting mix. Tamp down the mix so the surface is firm and level.

2. Poke Holes in the Mix:

Using your finger, make a hole in each cell of the starting mix. How deep the holes are depends on the crop you're growing. "Always read the instructions on the seed packets for specific information about planting depth and spacing," says Spoonemore.

3. Sow the Seeds:

Place seeds inside the holes you made in the mix. Follow the packet instructions for information on how many seeds should go into each cell of your container. "The number of seeds you should put into one cell of your container can vary depending on the type of seeds and the recommended spacing provided on the seed packet," says Spoonemore. "Many seeds are best sown one per cell."

4. Cover the Seeds:

Cover the seeds with more starting mix and tamp down. Follow the packet instructions for information on how much mix to use. "For very small seeds, a light covering of the seed-starting mix is sufficient, while larger seeds may need to be placed deeper," says Spoonemore. Water well.

5. Label the Seeds:

To help you identify the seedlings as they grow, be sure to label them accordingly. "Because so many seedlings look the same during the indoor growing process, it’s best to label each section," says McEnaney. "This isn’t just to keep things organized inside, but so that when you transfer them outdoors each plant is planted appropriately."

How to Care for Seeds Started Indoors

Know how to care for your seeds once they're sown to ensure proper growth.

Light

After sowing your seedlings, place them in a location with bright, indirect sunlight. "Ideally, provide 12 to 16 hours of light daily for optimal growth," says Spoonemore. "If you cannot provide 12 to 16 hours a day of light for your seedlings, use grow lights, either LED or wide spectrum fluorescent. Position the grow light several inches above your seedlings and raise it as they grow."

Water

Keeping the soil evenly moist while the seed is germinating is essential. "Since there’s relatively little soil, you don’t want to use anything with a fast spout that would cause the soil or seed to wash out of the tray," says McEnaney. "Use a spray bottle to keep the soil moist. If your trays are too deep to be saturated with a spray bottle, you can place another tray beneath and fill with water, allowing it to soak up to the roots." Check the soil's moisture regularly by sticking your finger about 1 inch into the mix and water when it feels dry to the touch.

Humidity

Keep the temperature within the range specified on the seed packet. "Many seedlings prefer a consistent room temperature around 70 degrees Fahrenheit," says Spoonemore. "Maintain humidity by covering the seed containers with a plastic dome or plastic wrap until the seedlings emerge." Gradually increase ventilation by removing the cover as the seeds sprout to acclimate them to lower humidity levels.

Fertilizer

After the seedlings develop their first true leaves (usually a few weeks after germination) start feeding them with a diluted, balanced, water-soluble fertilizer, says Spoonemore. Follow the instructions on the fertilizer package for the recommended dilution. "Avoid overfeeding your seedlings, as excess nutrients can lead to leggy growth and other issues," says Spoonemore.

How to Transplant the Seeds Outdoors

When your seedlings have grown strong and are a few inches tall with at least two sets of true leaves, they are ready for transplanting into larger pots or the garden, says Spoonemore. But before transplanting, your plants will need time to adjust—this process is called hardening off. "Move them outdoors into a sheltered area with filtered light, starting them out for a couple hours." says Spoonemore. "Gradually increase the time they are outside and expose them to more sunlight." In a few days, you can move them to their permanent home outdoors.