How To Start Seeds Indoors

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Before You Start

Growing plants from seed isn’t difficult, but it does take planning. Before rushing out and buying a bunch of random seeds and grow lights, consider these important variables:

• Your planting zone. Check the USDA Plant Hardiness Zone Map to make sure the plants you choose will thrive in your region.
• Time commitments. Seedlings may need six weeks to three months inside before transplanting, and you’ll need to keep an eye on them. Timers for lights and watering can help, but if you’re going on a 10-day cruise in the middle of April, consider that before starting.
• Cost considerations. “Seed is much cheaper than transplants, so you can get more plants for your dollar by growing from seed,” Campbell says. But buying planting equipment like lights, heating mats and timers adds up. And, of course, your time costs money, too. “So, it’s a balancing act,” Campbell says.

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Try Herbs First

If you’re new to seed-starting or gardening in general, it’s easy to get caught up in the excitement of growing your own food. But tending to hundreds of tomato and pepper seedlings may become overwhelming, especially if you aren’t used to it. That’s one reason Campbell loves herbs as an introduction to the world of growing plants. “Herbs are a great place to start because they grow readily from seed,” Campbell says. “They also produce a lot of seeds, so you can keep growing them.”

A south-facing windowsill is a perfect place to start an herb garden, or you can use artificial light. Popular, easy-to-grow herbs that do well indoors include chives, dill, thyme, parsley, sage, oregano, basil and cilantro. To fill your kitchen with herby fragrance, try lavender and mint, too.

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Pick the Right Veggies

Mastered the herb garden? Jumping right into growing tomatoes? For the best vegetable bounty, pick ones that do well starting indoors from seed. Not all do. “The best thing to do is follow the recommendation on the seed packet. It’ll tell you,” Campbell says. “Check days to maturity, and make sure you have a growing season that is that long in your area,” Eldred Steinkopf says.

Vegetables that take a long time from planting to harvesting are good candidates for starting from seed, especially if you have a short growing season. But Campbell has a tip for new gardeners: “If you look at the seed packet and it has an extremely long time to harvest, you might consider buying those as transplants.” Waiting for months to see growth can be discouraging.

Some plants should not be started from seed. A packet of any variety of cucumber, for example, will likely say to sow seeds directly in the ground outside when the soil is warm. Cucumbers grow fast, have a short harvest date and don’t like being transplanted, so there’s really no reason to start them inside.

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Gather Your Materials

If you’re just trying this out, it’s okay not to make a big investment. You can definitely start seeds on a sunny (unobstructed, south-facing) windowsill, according to Eldred Steinkopf. Until you know whether you’re starting an annual tradition: “Start small, start manageable, and build your way up from there,” Campbell says.

Here’s what you’ll need:

• Containers. “I’ve seen every variation possible: milk cartons, egg crates, old plastic jugs, plastic trays from the store. Ultimately, whatever you have on hand is best, but you can go as high-value as you want. They all work,” Campbell says.
• Adjustable light. You want the light source close to the seedlings as they grow, “so they don’t get too lanky,” Eldred Steinkopf says. Campbell says you can use LED or fluorescent, but he prefers LED. Pick one with a Kelvin rating between 4000K and 6500K.
• Rack or table. No matter how many seed varieties you’re planting, you’ll need a place to put them. Pick a spot that has access to electricity without an extension cord.
• Heat mats. A heat mat replicates “what happens naturally outdoors when the ground starts to warm from the sun,” Campbell says. “Heat mats help with germination, and I recommend them.”
• Timers. Seeds and seedlings need 12–16 hours of light a day, so get a timer to make it easier on yourself. “A surge protector with a timer is a great investment,” Campbell says. Watering can also be automated, but Campbell prefers manually watering so he can make adjustments as needed.
• Potting soil. “I would use a good seed-starting potting medium for all plants started inside,” Eldred Steinkopf says. “They are mixed exclusively for starting seeds successfully.”
• Fresh seeds. Seeds lose their viability over time, so don’t keep them around for more than two or three years.
• Labels. The seedlings all look pretty similar. Label the containers somehow so you know what’s what. Tongue depressors work well.

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How To Start Seeds Indoors

Depending on the plant type, variety, and your growing zone, you’ll likely be starting this process about two to three months before your average last frost date, if you have one. Some may only take six weeks, while longer-season plants take longer than average. Every plant has different requirements, so follow your seed packet.

• Set up your planting table with heat mats and lights, and arrange planting containers on trays to catch stray dirt and water.
• Poke a few holes in the bottom of milk cartons or other planting containers that don’t have drainage holes already. Fill with potting mix.
• Plant seeds according to the package directions. Seeds will have different planting depths and coverage requirements.
• Provide light or dark until germination (some seeds require one or the other). Check the packet.
• Keep the mix moist. “You can cover them to help with humidity and water retention, but it’s not really necessary,” Campbell says.
• Give plants 16 hours of light at first. “Once they start growing vegetatively, you can walk that back to 12 hours,” Campbell says. Keep the light two to four inches away from the dirt and/or seedlings.
• Water regularly, draining excess water out of the tray so the plants don’t get waterlogged.
• Harden off your transplants for two weeks before moving to the garden. “This means you are acclimating them to their new environment, and it is an important step for success,” Eldred Steinkopf says. “Take them outside to a sheltered area when the temperatures are above 50 during the day, and bring them back in at night.” Gradually increase the time each day.
• Prepare your garden for planting, and transplant your seedlings according to the packet directions.

About the Experts

• Spencer Campbell is the plant clinic manager at the Morton Arboretum in Lisle, Illinois, where he and Plant Clinic staff answer more than 10,000 plant questions each year from the public. Campbell got his start in environmental advocacy before turning to plant care and education. He’s been at the Morton Arboretum for ten years.
• Lisa Eldred Steinkopf is The Houseplant Guru and author of multiple books on houseplant care. She is regularly featured in publications across the web and in speaking engagements, where she shares her love and knowledge of all things houseplant.