Many gardeners like to start vegetable and flower seeds indoors during the winter months. It gives us a chance to shake off the winter blahs, keeps us focused on our favorite hobby and we get to eat tomatoes and peppers before our bought-seedlings-at-the-nursery-center neighbors do.
To the novice, seed starting can be intimidating, but it’s really quite easy. You don’t need much in the way of special equipment, but if you wish, you can utilize grow lights and heat mats for the best results.
First, you should understand that some plants are easily started indoors and some are best direct-seeded outside in your garden.
Vegetables That Do Well Started From Seeds Indoors:
- most herbs
- brussels sprouts
- most leafy greens
- many varieties of seed flowers
Not sure when to start seeds indoors? Check out these seed starting calculators.
Vegetables Which Are Best Started Directly in Your Garden:
- sweet corn
- Jerusalem Artichokes
- sweet potatoes
Minimum Requirements for Starting Seeds:
- Seed starting medium
- Plastic or biodegradable pots
- Very sunny window or grow lights
Peat pots vs starting trays: Many beginning gardeners use seed starting systems like the Burpee Seed Starting Kit or equivalent which has 1.5″ square cells to start plants. It’s a great system for beginners, but I found that I’m all thumbs when it comes to transferring the tiny seedlings from the small cells into larger pots. I use 3″ square or round pots and let the seedlings grow in them undisturbed until they’re ready for transplanting into my garden. It requires a little more space, but I’ve found that I have more success with the plants and better root growth.
Seed Starting Steps:
- Fill each starter pot with seed starting mix to within 1/2″ of the top and water until moist.
- Sow 3 seeds, spaced evenly around the center, and cover lightly with additional seed starting mix. (some varieties are left uncovered-read your seed packet directions)
- With your fingers, gently push down on the surface to remove any air pockets—the seeds need to come in contact with the starter mix in order to germinate.
- Mist with water until the potting medium is damp.
You’ll start most seeds indoors this way—some you’ll plant a little deeper, some you’ll let lay on the surface—refer to the planting directions that come with your seeds. Even though you’ll ultimately only keep one seedling in each starter pot, it’s best to use multiple seeds as a hedge against the chance that some of the seeds won’t germinate. That way, you’re not left with any empty starter pots.
Once all of the starter pots are seeded, place them in a shallow plastic tray to catch any overflow or spills and place near a sunny window (for just a few seedlings) or on a table where you’ll be using grow lights overhead (much preferred to a windowsill). Use a heat mat to encourage seeds to germinate faster, because faster germination results in a healthier plant.
Cover the starter pots with a sheet of translucent plastic or a plastic dome (available online) to seal in moisture—it’s important that the potting medium never dries out—the idea is to create a mini greenhouse. It’s easy to tell if it’s working—you’ll see condensation on the inside of the plastic.
Seeds Like a Cozy Room Temperature to Germinate
If you don’t use heat mats, make sure you keep the room air temperature around 70 degrees. Heat mats without thermometers do a good job of warming the starter medium sufficiently, but those with thermometers are even better, allowing specific control.
Lift the plastic sheet or dome each day to make sure that the top surface of the seed starter mix is still moist. When necessary, use a spray bottle to mist the top of each peat pot, getting the starter medium moist, not soaked.
How Long Does It Take for Seeds to Germinate?
The time it takes for your seeds to germinate depends on what you’re growing. Some will germinate in as little as 3 days and some will take 30 days or more. This information can sometimes be found on your seed packet.
Once the seedlings have germinated (the first leaves are showing), remove the plastic dome or sheeting. If you leave it on after this point, you may invite a fungal disease called damping off.
The surface of each pot will now receive more airflow, so they’re now more likely to dry out. From here on, the seedlings will have to be misted religiously at least once each day. As the seedling grows you’ll notice that the medium dries out faster—that’s because the plant is demanding more. It’s sufficient to just mist the top of each cell’s potting medium, as the seedling’s tiny roots are just underneath the surface at this point—don’t mist the leaves if you can avoid it, to guard against fungal infections. Once the seedling has emerged, add a small amount (a pinch) of granulated organic fertilizer just once—that’s all the nutrients the seedlings will need before moving into your garden.
Thin Your Seedlings
When the seedlings have grown their second set of leaves, they’re well on their way. Now the hard part comes: thinning. Look for the healthiest seedling in each cell – the one that’s growing sturdiest, greenest, leafiest, etc.—that’s the one you’re going to keep. Snip off the other seedlings in that cell with a small scissors. Do not pull out the seedlings you wish to discard, as this may damage the “keeper” seedling’s roots. The snipped seedlings will die in a few days.
Harden Off Seedlings Before Transplanting
When the seedlings are ready to be transplanted to your garden (anywhere from 4 to 12 weeks, depending on the plant), they’ll need to be hardened off for a week or more. Take your tray of seedlings outside every morning and place them in an area protected from direct sunlight, rain, and wind. The first morning, leave them outside for only an hour or two. Then, every day, give them a little more time outside until eventually, they’re outdoors 24/7. Each night, take them inside if the temperatures drop below 50. This gets the seedlings used to temperature and light fluctuations so they can withstand the outdoor weather. If you transplant your seedlings directly from stable indoor conditions to the fluctuations of the real outdoors, the seedlings may suffer stress shock and die.
How to Transplant Seedlings
When you transplant your seedlings into the garden, dig a hole at least twice as wide as the starter pot. If you’re using a biodegradable starter pot like a peat pot, gently tear down its sides and place it in the hole. Biodegradable pots are meant to break down in garden soil quickly, but occasionally they fail to do so and a plant’s roots can’t make their way through it. I’ve learned to tear down the sides to help this process along. Fill the hole with garden soil, press down into place with your hands to remove air pockets, and mulch with compost a few inches around each transplant. Water it in well.
For an in-depth exploration of seed starting, see Penn State Extension’s Seed and Seedling Biology.
Todd Heft is a lifelong gardener and the publisher of Big Blog of Gardening. He lives in the Lehigh Valley, PA with his wife, who cooks amazing things with the organic fruits, vegetables, and herbs he grows. When he isn’t writing or reading about organic gardening, he’s gardening.