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How To Start Seeds Indoors

February 22, 2022


It's Indoor Seed-Starting Time!

You may find yourself eager to get outside and start planting, but it’s best to wait until spring has sprung and the last frost date has arrived before planting tender seedlings in the ground. Here’s how to take advantage of the late winter months by starting your seedlings indoors.

Shop For Seeds

Gardening can be an expensive hobby. It doesn’t need to be, and starting your plants from seed is a great way to save money. Follow these tips to choose the perfect seeds for your garden.

Learn about types of seeds: F1 and F2 hybrids, heirlooms, which plants are open-pollinated (so you can save the seeds for next year), and what is patent protected.

Disease resistances are noted, so if late blight always takes out your tomato plants, look for resistant varieties.

Drought-tolerant varieties that stand up to summer heat are especially helpful to gardeners in warmer climates.

The number of days to maturity is important, especially for northern gardeners whose growing season may come to an abrupt halt before their plants start producing anything edible.

Make note of the number of seeds in a packet. If you are getting 100 broccoli seeds, maybe you can team up with your neighbors and pool your orders. 

You can also save seeds from your garden by selecting seeds from the most suitable plants, harvesting them at the right time, and storing them properly until you need to plant them. 

Not ALL seeds should be started indoors. 

Crops that are best started indoors include broccoli, brussels sprouts, cabbage, tomatoes, cauliflower, celery, eggplant, and peppers.

Tender vegetables like tomatoes, eggplants, and peppers are very susceptible to the cold temperatures of spring, so it’s best to start them indoors and keep them safe from unpredictable weather. They will also benefit from being transplanted to a larger container and growing on before you plant them in the garden.

Transplant when it gets to 45-55 degrees at night for the tomatoes, but eggplants are a bit pickier. Don’t set eggplants out until the soil temperatures are 55-60°F (about 2-4 weeks after the last frost date).

Plants like radishes and peas are so fast-growing and cold-tolerant that it just makes sense to get them right in the ground!


Detailed Seed Starting

Seed Starter Mix
These mixes don’t contain any actual soil, but they provide ideal conditions for sprouting seeds. Most importantly, they provide a good balance of drainage and water-holding capacity, and they minimize problems with disease on vulnerable seedlings. If possible, don’t use garden soil to start seeds indoors; it generally doesn’t drain well and may contain plant disease spores.

You can use recycled pots, for example, empty yogurt containers, but be sure to poke holes in the bottom for draining, so that your seeds are not over-watered. Plastic six-packs and flats are good choices and can be reused year after year. Biodegradable pots are fine, too.

Before you fill your containers with the soilless mix, add enough water to moisten it and mix it with your hands. Squeeze out the water. The perfect ratio of water to soil is when you squeeze your soil very hard and a few drops of water come out of it.

Put two or three seeds in each cell. This way you’re guaranteed at least one plant will germinate. Then cover with the mix. 

Press down on the soil with your finger to make sure the topsoil is touching the seed. Seeds need to be in contact with all the soil around them to germinate well.

Cover with a plastic dome to create heat and humidity to allow the seeds to germinate. Remove the lid after the seeds sprout then place under grow lights or a south-facing window. Adjust the height of your lights as your sprouts grow.

Water your plants by putting water into the drip tray and allow the plants to soak up the water for 10 minutes. Any water left in the tray afterward should be dumped out to prevent overwatering.

Use a half-strength fertilizer once your seedlings have one or two sets of leaves. Organic fertilizers are a good choice since they provide a range of nutrients, including micronutrients.


For especially tiny seeds like poppies or snapdragons, you can use sand to cover the seeds. It’s finer than soil and will help keep moisture in.

If they all grow, just weed out the runts by cutting the stem off at the soil level. Don’t pull it out, because this will disturb the soil of the other seedlings. 

Place your tray on a heated seed mat to speed the germination.

LED lights should be 8-12 inches from the top of your plants, possibly more if it’s a setup with very strong lights. T5 bulbs should be 5-6 inches from the tops of your plants. 

Seed Tray

Interesting Tips

Seeds don’t need light to germinate. They need heat.

Seeds need moisture to germinate.

Water from underneath.

Keep a fan going to prevent “damping off”.

Use whiteboards to reflect light to plants.

Use a timer on your lights – seedlings need 15 hours of light unless they’re onions.

Run your hand across the top of your seedlings. It strengthens them.

Visit The Art Of Doing Stuff for more helpful and interesting gardening tips:

Thinning & Harding Off

You want one seedling per pot, so choose the healthiest, strongest-looking seedling to keep. Snip the other seedlings off at the soil line and discard them.

Your seedlings are large enough to transplant in your garden once they have three to four true leaves and have been hardened off.

What does harding off mean?
Up until this point, your seedlings have been protected from wind, rain, cold, heat, and intense sunlight. They need to toughen up before you transplant them in your garden. In general, the process of hardening off will take about one week, and sometimes up to two weeks if the weather has an unexpected and dramatic drop in temperatures.

Start hardening off your plants after the last frost date. Usually around May 15th for central Ohio.

Your seedlings need some protection from wind and sun during their first hours outside. You have a couple of options including a shady spot against your home, a table under a tree, or inside a cold frame. Move plants back indoors at the end of the first day or close the lip on the cold frame. 

Lengthen the hardening off time for an hour more each day.

Alter the shade or move the seedlings to a location that receives morning or evening sun, so they are exposed to a little more sun each day. Allow the seedlings to experience gentle breezes. Even filtered sunlight and light breezes can deplete your plants’ moisture. Check on them frequently and give them enough water, so they do not wilt.

Eventually, allow your plants to stay in full sun and outside overnight as long as night temperatures do not drop below freezing. If it is going to get below freezing move the plants indoors. Resume the hardening off process once temperatures return to normal conditions.

Cold Frame


Prepare your beds: If you haven’t done so already, prepare your garden beds by removing all the weeds and adding some compost and fertilizer. If the weather has been dry, prepare and water the bed very well the day before you plant.

Water: Water the seedlings well before transplanting. This will help contain the soil and prevent transplant shock.

Review your garden map: Bring a copy of your garden map out to your vegetable garden. Refer to your map and plot out where the seedlings will be planted in each bed.

Dig your holes: Use a shovel or trowel to make a hole in your garden for each seedling. Make the hole a little wider than your container, but about the same depth. (Exception: If you are transplanting tomatoes, try to bury as much of the stem as you can. Unlike other plants, tomatoes will grow extra roots along the portion of the stem below the soil.).

Remove the plant from the pot: Remove the seedling carefully from its original container by squeezing the sides of the container and inverting it while holding your hand over the soil so the base of the plant is between the index and middle fingers. Tap the bottom of the container several times and the root ball should slide out of the container. Try not to mangle the roots or pull from the stem.

Plant the seedling: Gently center the plant in the hole, pull the soil in from the sides, and firm it in lightly.

Water well: Use a watering can to deliver a gentle shower of water at the base of the plant. Continue to water frequently until the seedlings become established and begin to grow. Once the seedlings become established, let the soil dry slightly between watering.

Mulch to hold in soil moisture: Once the seedlings become established, mulch the beds to help suppress weeds and hold in soil moisture. Keep the mulch a few inches away from the stems of your seedlings so it doesn’t smother the plants.