What Seeds To Start Indoors

Seeds need warmth to germinate, but not every one of us is blessed to have warm and sunny weather all year round.

So the best thing we can do is to start seeds indoors to give them the best seed starting conditions and just transplant them outside when the weather warms up. 

But not every plant does well in transplanting, so we prepared a list of different types of vegetable seeds you can start indoors!

Lettuce Seeds

Lettuces are incredibly easy to grow, and you can actually grow them completely indoors!

But even if you’re planting them in your garden, they will do great if you start them indoors, especially when the weather is hot, because lettuces don’t like the heat.

Lettuces do well in the cold, but if the soil is too cold, the seeds will germinate slower. 

So to avoid both heat and cold weather, starting lettuce indoors is ideal.

They germinate best at about 70˚F or about 21˚C.

Lettuce grows quickly, so you’ll need to use individual peat pots instead of flats so you can avoid planting up inside.

You’ll want to sow a few lettuce seeds in each peat pot about three weeks before your last predicted spring frost. 

Plant lettuce seeds about 1/4 inch deep. If you’re starting indoors, you should be seeing sprouts in two to ten days.

Place a few seeds in peat pots filled with organic starter mix, then place them under a humidity dome and wait until they sprout.

Once sprouts appear, remove the humidity dome and provide your sprouts lots of light via the sun or a grow light.

Thin to the best-looking lettuce seedlings when they’ve got two true leaves. Harden off the plants before you transplant them. 

Onion Seeds

Onion plants are easy to grow indoors. They need warm temperatures and lots of light.

Onions from seed should be grown in flats or pots. Start your onion seeds ten weeks before the last expected frost date. So, you’ll be starting your onion while it’s still winter.

Prepare a medium-sized container, about 4 inches by 6 inches and fill it almost all the way with your seed starter mix.

Onion seed is a type of seed that is really tiny, so just sprinkle tons of seeds into two half-inch deep lines and loosely cover them with soil.

Once you start seeing germination on the sown seeds, you should be ready to harvest your greens. You’ll want to plant around four seedlings in each spot.

They can take a while to germinate, so be patient. But once they grow greens, you can already enjoy those as soon as they reach about 4 inches tall. 

Transplant the seedlings after any chance of frost have passed. 

Tomato Seeds

Tomatoes need warmth to germinate and grow well. They also like to stay warm during the day so starting them indoors is a great way to grow them. 

Tomato plants need warm temperatures to grow well. You can even use a heat mat to help the germination of the seeds.

They thrive at about 80˚F or about 27°C, but they will also germinate in temperatures as low as around 60˚F or 15°C.

Starting tomato seeds indoors helps ensure that your plants grow quickly and strong. You can use a humidity dome to speed up the process.

Sprouting seeds takes 5 days to 2 weeks, and that’s when you can open the humidity dome. Remove the humidity dome and heat mat when almost every seed has sprouted. 

When the plants have grown true leaves, they are ready to be transplanted and need to be potted up.

Cut the seedlings you do not want to keep from the cells and plant them in bigger pots.

Sprouting seeds need lots of light. Pot them deeper, so they don’t become leggy.

Also, make sure the soil is warm and doesn’t get too cold or fluctuate. And, don’t forget to harden off before planting.

Pepper Seeds

Pepper plants love warm weather and don’t do as well in cooler soil temperatures. So it’s best to wait for the outdoor soil temperature to warm up before planting them. 

You can plant your pepper seeds directly into the garden after the last frost date, but peppers take a long time to grow, so it’s best to start them indoors. 

You can plant them around the same time as your tomato, even earlier. Start your pepper a week before your tomatoes. This is because peppers take a really long time to germinate.

Seeds should be planted about 1/4″ inch deep, watered well, placed under a humidity dome, and kept warm until they sprout.

Humidity domes and heat mats should be removed as soon as the seeds start sprouting and give them plenty of sunlight or provide a grow light.

Like any plant, they’re ready to be transplanted when they have true leaves. Peppers also need hardened off and transplanted when it’s warm. Wait for the temperature to be warm. Wait a couple of weeks after the last predicted frost before transplanting them just to be safe.

Broccoli Seeds

Broccoli is an easy-to-grow vegetable that can be harvested twice a year. Starting broccoli from seed indoors when temperatures are still low, and the danger of frost exists is helpful.

Broccoli is a challenging plant to start indoors, but it can be done.

Start your broccoli about 7-9 weeks before the last predicted frost in your area. For fall crops, start indoors about 10 to 12 weeks before the first predicted frost.

Like lettuces, broccoli also germinates best at cool temperatures or about 70˚F or 21˚C.

Place two of your favorite broccoli seeds per cell and sow them 1/4 inches deep in seed starting mix, water and then place them under a humidity dome and wait until they sprout.

Once sprouts appear, remove the humidity dome and provide your sprouts lots of light via the sun or a grow light.

Repot or thin the seedlings after they get two true leaves. Spend some time hardening off your plants before transplanting.

Cabbage Seeds

Cabbages need a long growing season, so starting seeds early indoors is beneficial to them.

Start cabbages indoors 4-6 weeks before the last expected frost. They also germinate best at cool temperatures or about 70˚F or 21˚C.

Sow them 1/4 inches deep in seed starting mix and water and then place them under a humidity dome and wait until they sprout.

Once sprouts appear, remove the humidity dome and provide your sprouts lots of light via the sun or a grow light.

Only transplant them after hardening off for a few days. You can also thin the seedling if you prefer. 

Winter Squash Seeds

Squash bugs are destructive pests that can destroy your plants if left unchecked.

Starting squash indoors helps prevents any squash bug attacks. The seeds also won’t germinate in cold weather or 66˚F or around 19˚C and below. 

Winter squash takes a long time to mature, but starting them indoors allows you to control the growing conditions they’re in.

Because they have bigger seeds and can grow into larger plants, it’s best to plant them in an individual 2 to 4-inch pot. Sow 2 seeds in each pot for more chances of germination. 

Start them 4 weeks before the predicted last frost. They will take around 4 to 10 days to germinate. Cover them with a humidity dome and wait until they sprout.

Remove the humidity dome when the germination starts and give them some light. 

As usual, you can thin them out when they grow true leaves, and you need to harden them before transplanting. 

Tips! 

• It’s best to plant multiple seeds per insert for more chances of success in germination. Learn more about that here.
• When thinning the seedlings, don’t pull the weaker seedlings or weaker plants out of the soil; this can damage the roots of the one you want to keep. Instead, cut the stems off. 
• For plants that prefer warmth, you can use heat mats if you have one, but if you don’t – put them on top of your fridge! We all know how warm that can be. 
• When using a heat mat or grow lights, pay attention to the soil. The heat can make the soil dry, so water as needed to keep the soil moist. 
• For plants that need warm soil, it’s better to keep your seedlings indoors and wait an extra week or so before transplanting them or wait before the soil temperatures warm up.
• Harden off the plants before you transplant them. Hardening any starts is best on an overcast day with calm winds.

Did you know?

The “days to maturity” information on most packets of seed for plants pre-started indoors indicates the time it will take to see crop after you transplanted 6-week old starts? And some starts will take longer before they’re ready to transplant. Seed companies indicate that on the seed packet (probably) to encourage you to plant because seeing the actual planting time and how long it will actually take to get a crop might be disheartening. 

Other seeds that will do well when started indoors:

• Cauliflower seeds
• Celery seeds
• Cucumber seeds
• Eggplant seeds
• Corn seeds
• Peas