15 Vegetable And Flower Seeds To Start Indoors

Starting seeds indoors is a great way to get a head start on your gardening season. While some vegetables, herbs, and flowers grow best when directly sown, others need that jump start of being started indoors. Here you’ll find a list of the top 15 seeds to start indoors for a thriving garden.

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Getting a head start on the garden always sounds like a great plan and starting seeds indoors is a great way to accomplish that. But not all seeds are created equal and while some tender, heat-loving crops like tomatoes and peppers need started indoors virtually everywhere, other crops like carrots need to be directly sown.

While many crops won’t need to be started until around 6 weeks before the last frost, other plants need much more time to germinate and grow, so it’s best to get out a garden planner and write down when to start each of the following seeds to help you stay organized. Everything will be USDA zone-based, so knowing your USDA gardening zone is important to know when your last expected frost is.

Vegetable Seeds to Start Indoors

Lettuce

Growing lettuce is easy, but since it doesn’t like it hot, it’s best to start indoors 3-4 weeks before the last hard frost where the low temperatures are around 28°F. Some varieties can be grown in even colder temperatures and can be started around 8 weeks before the last frost.

It is best to start lettuce in individual peat pots or soil blocks, around three seeds to a pot. Thin them after they have two sets of true leaves, leaving only the strongest plant. Be sure to provide them with 6 to 8 hours of direct light via a grow light for the best outcome.

Broccoli

While slightly more difficult to grow than lettuce, growing broccoli is pretty straightforward and another crop that you can get two harvests from.

Unlike lettuce, broccoli doesn’t withstand cold temperatures quite as much, but it will begin to bolt (flower) in high temperatures, just the same.

Start broccoli 7-9 weeks before the last frost, or 10 to 12 weeks before the first frost if growing a fall crop. You can start broccoli seeds and flats as they do best when potted up a time or two and then transplanted outdoors.

Tomatoes

Tomatoes are slightly finicky, heat-loving, tender plants but growing tomatoes is quintessential to the backyard garden.

Since tomatoes thrive in heat, starting them indoors is essential to harvest a crop in just about any gardening zone. Generally, you’ll start seeds indoors about 6 to 8 weeks before the last frost.

While not completely necessary, using a heat mat to help speed up germination is helpful. Seeds can be started in flats and then potted up 2-3 times before hardening off and transplanting outdoors once temperatures are well above 50°F on average.

Peppers

In most places, like tomatoes, peppers have to be started indoors. Their growing season is long, but most of us don’t have the temperatures to support them.

Peppers are usually started a week or two before tomatoes simply because pepper seeds take a while to germinate, even with a heat mat. Starting them 7-9 weeks before the last frost will help give them the head start they need to germinate.

Peppers also benefit from being potted up two to three times before being transplanted outdoors.

Cabbage

Another cool weather-loving vegetable, cabbage can be helped to get amazing harvests by beginning them inside. Much like lettuce, it can be succession planted for continuous harvests until the hot weather takes over.

By starting the seeds indoors, you not only get a jump start before the soil is typically warm enough to get germination outdoors, but you can help combat cabbage worms because the larger plants are much easier to cover.

Start seeds 4-6 weeks before the last expected frost. Thin the seedlings once true leaves form and transplant them outdoors into workable soil after hardening off.

Winter Squash

Starting any squash indoors has its advantages. It helps with potentially devastating squash bugs when you start the seeds indoors.

Winter squash in particular can take a while to grow to maturity, so in most climates, it’s recommended to start them indoors. Zucchini and other summer squash grow so quickly and prolifically that you can direct sow if you choose.

Squash seeds do best when planted in individual peat pots because they get large quickly, you’ll want to sow two seeds in each about 4 weeks before the last expected frost. Thin once they begin to get their true leaves, harden off before transplanting.

Onions

I much prefer growing onions from seed as opposed to sets as they provide a larger variety. Unlike the previously mentioned seeds, onions are one of the first seeds you’ll start indoors, approximately 10 to 12 weeks before the last predicted frost.

A large 4″X6″ container is the perfect size for starting onion seeds. Simply sow two lines all the way across the container and sprinkle a little soil on top of them. Onions take a while to germinate but keeping them under plenty of light and keeping the soil moist via a spray bottle will help with germination.

Once the onions sprout, you can clip the greens after they reach about 4 inches in height. Transplant seedlings after the danger of frost has passed.

Brussels Sprouts

Growing brussels sprouts is easy and they don’t take up a lot of space, but they do need to be started indoors about four weeks before the last expected frost.

Brussels sprouts are a long-season crop that won’t be ready to harvest until autumn and take about a week or two to germinate. Unlike some of our hot temperature-loving crops, do not use bottom heat on Brussels sprout seeds.

Once sprouted and the first two sets of leaves appear, thin and fertilize twice a week. Brussel sprouts are ready to be transplanted outdoors once they have at least four or five sets of leaves.

Cucumber

Cucumbers grow best in warm weather, so get a head start by starting these seeds indoors a few weeks before the last frost. Starting them much earlier means they’ll likely become root-bound or too large before they can be transplanted outside.

Starting cucumbers inside also helps avoid the cucumber beetle, which prefers young, tender plants. Simply sow 1 to 2 seeds per cell. If you start them more than 3 weeks before the last frost, anticipate potting up into 6″ pots before you harden off the seedlings and place them outside.

You can thin to just a single seedling per cell after the first two sets of true leaves appear. Be prepared to provide a cucumber trellis once transplanted outdoors.

Eggplant

Much like tomatoes and peppers, eggplants are a long-season, heat-loving plant. Because of this, they benefit from being started indoors.

Start seeds eight to ten weeks before the last frost, in individual peat pots for the best results. They love humidity and heat so using a heat mat and humidity dome will also be helpful.

Transplant the seedlings outdoors after the last threat of frost has passed and the temperature is at least 60°F.

Flower Seeds to Start Indoors

Pansies

While finicky to start from seed, with a little finesse pansies can be grown from seed. For early blooming, you’ll want to start the seeds 10-12 weeks, possibly earlier.

Pansies are a seed I recommend starting in January for the earliest bloom. Surface sow the seeds, but make sure they’re in good contact with the soil. Then, cover the seeding tray with a plastic bag.

Place the tray in a cold location for a few days and begin checking for germination. Once germinated, place them under lights.

Snapdragons

My favorite snapdragon is the apple blossom snapdragon. They’re dainty and pretty and bloom all season for me, but I cannot find them locally, so I start them from seed.

Not quite as finicky as pansies, snapdragons also need to be surface-sown 10-12 weeks before the last frost. However, they need light, not cold, to germinate. They’ll begin sprouting within 7 to 14 days.

Once germinated, you can thin them to the strongest plants, keep them adequately moist, and transplant them outdoors a week or two before the last frost.

Marigolds

Marigolds are very easy to grow from seed. While usually prolific in our area, I actually had a difficult time finding them last year, so starting these easy-to-grow flowers from seed can always work in your favor.

Start them in seed trays about 6 to 8 weeks before the last anticipated frost date in your area. They like warm soil, so a heat mat can be beneficial for quick germination as well. You should begin seeing sprouts within 4 to 14 days.

Thin to the strongest seedlings after the first two sets of true leaves appear. Transplant outdoors after the threat of frost has completely passed.

Coneflower

Coneflowers can be grown much like pansies from seed in order to get a head start on the season. These beautiful, herbal plants are easy to grow but do need some cold stratification in some form or another.

Sow seeds in a flat filled with potting soil, cover it with a clear plastic bag, and place the whole thing in the refrigerator or other cold spot for 8 to 10 weeks. Once the cold stratification period has passed, place the tray under the grow lights. You should see germination within 10-14 days later.

After germination begins, remove the plastic, and thin to the strongest seedlings. Transplant outdoors after the last frost in a sunny location with well-draining soil.

Lavender

Growing lavender from seed is actually pretty easy. Like many of the aforementioned flowers, lavender also requires a period of cold stratification. However, I have good luck with simply throwing the seed packet in the refrigerator for 8 to 10 weeks before I start the seeds.

Surface sow the seeds around 10 to 12 weeks before the last expected frost after a period of cold treatment. Be sure to use a spray bottle to keep the soil moist, but not too wet. They can take a while to germinate, anywhere from a few days to a few weeks, so be patient.

Transplant outdoors after the last threat of frost has passed. Most plants will bloom in their first year, though some may be shy.

15 Vegetable and Flower Seeds to Start Indoors