How to Germinate Seeds Indoors Successfully

Gazing out your window into the gray and icy abyss can make your heart hungry for, well, some greenery. While a lush garden with showy blooms isn’t exactly in the cards in the coming weeks, one thing you can do is start germinating seeds inside well ahead of spring. Learning how to start seeds indoors is a pretty simple process. We’ve got the full how-to below, and it’ll set your growing season up for wild success.

Benefits of Germinating Your Own Seeds 

Along with giving your green thumb something to do throughout the chilly season, germinating seeds indoors offers quite a few benefits. For starters, it gives you a longer growing season. 

“Starting plants like vegetables indoors gives you weeks of extra plant growth before temperatures are right to plant outdoors,” explains Madeline Hooper, gardening expert and host of the PBS show Garden Fit. “Also, better germination takes place in a controlled indoor environment, and you can watch close-up the way little seeds grow into plants—just amazing.”

Another benefit is that it’s cost effective, since starting plants from seed isn’t as expensive as buying seedlings or more established plants. This is especially true for perennials.

How to Germinate Seeds Indoors  

Germinating seeds indoors is a pretty straightforward endeavor, though there are some tiny tweaks you’ll need to make depending on the type of plant. When in doubt, refer to the on-label instructions or do some research on the specific type of seed you’re growing. Otherwise, you can follow this general step-by-step guide on germination. 

Step 1: Create a Controlled Environment 

In the same way you thrive in a cozy space conducive to life’s needs, your seeds will do best in the right environment. Here’s what you’ll need: 

• Grow lights (LED lights, full sun windowsill, or older fluorescent with cool and warm T8 bulbs)
• Seed starting mix, and ideally a sterile potting mix
• Watering can that has a fine rose attachment and/or a mister
• Plastic wrap or humidity dome
• Seedling containers (you can purchase or make your own—paper egg cartons are popular for this) 
• Heat matts
• Labels, since all seedlings look very similar to each other 

Step 2: Choose and Prep Your Seeds 

Not all seeds are the same. Some can be placed right into soil while others require extra care. Start by choosing high-quality seeds from a reputable source, then refer to the seed packet for specific instructions.

In many cases, larger seeds need to be pre-soaked, notes Andrew Porwol, a seasoned gardener and founder of Sapcote Garden Centre, while others require a process called “scarification” that involves gently peeling the seed coat to encourage germination.

Here’s what you’re apt to run into on germination instructions: 

• Soaking: Larger seeds like peas and beans benefit from a short soak (four to 12 ) in room-temperature water to speed up the sprouting process.
• Stratification: Seeds from plants like lavender or milkweed may need to be stored in a damp paper towel inside a refrigerator for a few weeks.
• Scarification: Tough-coated seeds (like morning glories) may germinate faster if you lightly scratch them with sandpaper or nick them with a knife.

Step 3: Plant Your Seeds 

Once your seeds are prepped, you can officially plant them. Fill your seedling containers with the sterile seed-starting mix, gently patting it down to remove air pockets. “To germinate seeds indoors, use a light, well-draining seed-starting mix in small containers or trays with drainage holes,” Sears instructs. 

She says to moisten the mix before planting so it’s damp but not soggy. Follow the depth guidelines from the seed packed and sow sparingly to prevent overcrowding. Place under/in the light with your humidity dome or plastic wrap on top. 

“Germination rates are greatly increased when bottom heat from a seedling heat mat is used, particularly for plants that prefer heat, such as peppers and tomatoes,” Porwol adds. Either way, a warm environment between 65 and 75 degrees Fahrenheit is best. 

Step 4: Nurture Your Sprouts 

Here’s where your green thumb can really go into overdrive. For success, you’ll want to keep the environment stable for successful germination. That means ensuring your seeds have enough light, are kept warm, and get moisture. 

On that note, keep the soil evenly damp but avoid overwatering, which can lead to mold or “damping off.” Use a mister or fine-rose watering can for gentle hydration. Once seedlings emerge, remove the plastic wrap or dome gradually to prevent sudden moisture loss.

Step 5: Transplant 

Once your seedlings develop two sets of leaves, they’re considered strong enough to transplant. If it’s still too cold outside, transplant them to a medium to large sized pot, otherwise, you can plant them directly into the ground. Just make sure you do this gradually so it’s not a shock to their system. 

About a week to 10 days before transplanting, Hooper says to begin exposing seedlings to outdoor conditions for a few hours each day, gradually increasing their time outside. Referred to as “hardening off,” this strengthens their stems and prevents transplant shock.