21 Seeds to Start Indoors in March

For many gardeners, the end of winter is finally on the horizon. We can see the light at the end of the gloomy winter tunnel. Unfortunately, that’s not the case for all gardeners. This month, for those in zones lower than zone six and below, it probably feels like winter is never-ending.

No matter which group you fall into, there are plenty seeds to start this March if you’re sowing indoors.

Sowing seeds indoors (or in a protected area like a greenhouse) gives you much greater control over growing conditions. With a few tools like heat mats and grow lights, you can improve germination rates and give your seedlings the strongest possible start. Indoor sowing also means easier access to your trays, so you won’t forget to water or keep an eye on them while they’re germinating.

If you haven’t started indoor sowing in February, March is a great time to sow a wide range of vegetable, herb, and flower seeds, depending on your spring gardening goals.

Cabbage

As a brassica, cabbage loves cooler temperatures, making it perfect for seed starting in March. This crop is a staple in my vegetable garden due to its versatility. You get so much to work with in one harvest, and the leaves are useful in cooked dishes or eaten fresh. I like to use them as a nutrient-dense and crunchy replacement for lettuce in salads when my leafy greens run out.

Indoor sowing is recommended for those in cooler climates around 6 to 8 weeks before your average last frost date. If you live in a warmer climate where frost has already passed (zones 8 or 9 and up), your cabbage will perform better if you wait until fall to sow for a cool-season harvest.

Broccoli

Sticking with brassicas, broccoli is another excellent seed to start in March. Although broccoli gets a bad rap from kids in many families, this is one of the most nutrient-dense vegetables you can grow. Choosing your own varieties by growing from seed also gives you more control over flavor or even color (with options like Burgundy).

Get your kids involved in the sowing process, and they’ll be much more likely to enjoy broccoli when it appears on their plate a few months later.

Broccoli is best sown indoors 4 to 6 weeks before the last frost, a little later than cabbage. Like cabbage, if you live in a warm climate, it’s best to wait until fall to avoid your broccoli maturing in hot weather.

Cauliflower

Whether you’re turning the heads into cauliflower rice, cauliflower pizza bases, or one of the other trendy cauliflower dishes, I guarantee this vegetable is more versatile than you think. If you haven’t tried growing them before, March is a good time to start.

You can follow the same planting instructions for cauliflower as for broccoli, sowing 4 to 6 weeks before your last frost date indoors. Don’t plant them too deeply—a quarter of an inch below the soil is all they need for germination. The seedlings should emerge in 8 to 10 days.

Lettuce

Leafy greens are a must-have in any vegetable garden. They’re easy to grow and super versatile, making them a great crop for beginners.

Outdoor sowing is recommended for many lettuce varieties, but it is possible to sow lettuce indoors 4 to 6 weeks before your average last frost date. You can even continue to grow it indoors with the help of a grow light and containers, allowing you to harvest fresh lettuce leaves even if it’s still snowing outside.

Lettuce grows best in cool weather and tends to bolt when it’s too hot. If you live in a warmer climate, your lettuce will perform better sown in fall for winter harvesting to avoid bolting.

Kale

Kale is a cool-season green known for its impressive nutritional value and large, tasty leaves. If you haven’t started your kale seeds indoors already, March is a good time to sow. The ideal sowing window indoors is 4 to 6 weeks before your average last frost date.

Don’t start these seeds too late. Like other cool-season crops, they don’t perform well in warmer weather. If you live in zones 5 to 7, you can also start seeds in March outdoors as long as the soil temperature is above 45°F.

Bunching Onions

Bulb onions are started quite early (often in February) as they take a while to germinate before being transplanted outdoors. However, if your last frost date is a little closer, March is a good time to sow bunching onions.

Bunching onions are a great way to add that essential onion flavor to your dishes without the same patience required before harvesting. They grow in many different soil types, are tolerant of heat and cold, and can be continuously sown throughout the season for a seemingly endless supply.

Ready to harvest in just 2 months and useful in many dishes, bunching onions should be a staple in any vegetable garden. For indoor sowing in March, plant 8 to 10 weeks before your average last frost date and transplant your seedlings out 4 to 6 weeks before your average last frost date. These plants are cold tolerant and don’t mind the initial chill before the spring season arrives.

Celery

For gardeners in zones 3 to 5, there aren’t many crops to sow now. However, celery is one seed to start in March indoors because it needs a long period to germinate.

Indoor sowing is recommended 10 to 12 weeks before your average last frost date if you want to harvest in spring. You can also sow indoors 10 to 12 weeks before transplanting outdoors in fall if you want a cool-season harvest.

Celery is sensitive to root disturbance, so it’s best to plant in biodegradable pots that can be transplanted straight into the ground.

Tomatoes

Summer may feel like an eternity away, but you can lay the foundations for your summer garden in March by starting seeds like tomatoes. Starting tomato seeds indoors ensures your seedlings have the strongest possible start, limiting growth issues later on.

When sowing indoors, plant 4 to 6 weeks before you plan on transplanting. This is usually 1 to 2 weeks after your average last frost date when the air temperature is at least 45°F to avoid cold damage to the young seedlings. You can also plant a little earlier and keep cold protection ready.

As a summer crop, a seedling heat mat is helpful when germinating. The soil temperature needs to be at least 70°F, preferably closer to 80°F.

Eggplant

Like celery, eggplant is another seed to start in March for those in cold regions. They need to be started indoors early, giving them plenty of time to germinate and establish strong roots before they move out into the garden. You may only see the fruits in summer, but this early start will give you the foundation for a strong crop later on.

Sow your eggplant seeds 10 to 12 weeks before your average last frost date. Only transplant outdoors 1 to 2 weeks after the last frost when the soil temperature is at least 60°F.

Eggplants love heat, so the soil temperature when germinating should be around 80°F. Only transplant outdoors when you are sure there won’t be any upcoming cold snaps.

Peppers

The final vegetable on this list is another warm-season staple: peppers.

Peppers take a long time to germinate, sometimes up to a month. Some varieties are fussier than others and need the perfect conditions for germination. Starting them indoors is recommended to give you the best control over this environment, improving germination rates and ensuring they get the heat they need to grow well.

The soil temperature for germination should be between 70°F and 90°F. Sow 8 to 10 weeks before you plan on transplanting, around 2 to 4 weeks after your average last frost date. Peppers will die quickly if temperatures are too cold, so wait until daytime temperatures are at least 70°F before you consider transplanting.

Basil

I believe you can never have enough basil in an herb garden (mostly because I frequently make my own basil pesto). If you’ve made pesto before, you know you need plenty of leaves, which is why planting multiple basil plants is so useful. This herb also pairs well with any dish that calls for tomatoes.

One of the great things about basil is the varieties available, allowing you to choose different colors, sizes, and flavor profiles to suit your needs.

Start seeds indoors 4 to 6 weeks before transplanting outside when nighttime temperatures are at least 50°F. Continue sowing every 3 weeks, around 3 to 4 times, to ensure a continuous supply. They take a while to grow back after harvesting.

Oregano

If you love Mediterranean dishes, you need oregano in your garden. These tiny leaves are packed with scent and flavor, pairing well with tomato dishes just like basil. They also work well on meat and fish dishes or paired with other Mediterranean herbs in a dried mix.

Start oregano seeds indoors 6 to 8 weeks before your average last frost date. If you can’t get the soil temperature warm enough, place the trays over a seedling heat mat.

Thyme

Like oregano, thyme is another herb that works well with most meat dishes. The leaves have a subtle earthy flavor that pairs well with a variety of foods. Another benefit of growing thyme in your garden is the adorable edible flowers that can be harvested or left on the plant to attract pollinators.

You can follow the same planting instructions as for oregano. Do not plant the seeds too deeply, as they need light to germinate. After planting, they should emerge within 10 to 15 days.

Sage

Sage is a great ornamental and edible plant. The soft gray-green leaves and purple-blue flowers look great in the garden and attract pollinators, making it an excellent landscaping plant. The leaves are just as useful in the kitchen, often paired with pork, cheese, and other high-fat foods.

Sage performs best when started in trays indoors 6 to 8 weeks before your average last frost date. Use a well-draining seed starting mix and monitor moisture levels to ensure even germination.

Rosemary

Rosemary is great on its own but also pairs well with all the other herbs on this list, indicating its versatility. You can pair it with meats, vegetables, and just about anything that needs a unique woody flavor.

It also adds ornamental value, with needle-like leaves and adorable purple flowers that look great left on their own or trimmed into a more formal hedge shape.

Rosemary needs plenty of time to germinate and establish before transplanting outdoors. Start seeds in March if your last frost date is 10 to 12 weeks away.

Marigolds

Bright marigold flowers are sure to liven up your garden after a gloomy winter. There are many types and cultivars to choose from, and many of them are edible. Compact varieties like ‘Lemon Drop‘ also look great in containers, making them ideal for gardeners with limited outdoor space or anyone who wants to add a pop of color to their patio or balcony.

Indoor sowing is recommended around 4 to 6 weeks before your average last frost date. After starting seeds in March, seedlings will emerge in 1 to 2 weeks.

Alyssum

Sweet alyssum is the ideal flower to fill any gaps in your garden. It is compact and explodes with flowers from spring to frost, releasing their sweet fragrance all season long. It also grows well in containers, particularly hanging baskets, if you want to keep it close by.

Sweet alyssum performs better and flowers more prolifically in cooler weather. Start seeds in March 4 to 6 weeks before your last frost date, and keep them in a sunny spot but protected from excessive heat, particularly in summer.

Morning Glory

Morning glory flowers are sure to catch your eye wherever they are planted. The colorful blooms appear from summer until the first frost and come in a range of fascinating hues. Cultivars like ‘Flying Saucer‘ have massive blooms with blue and white striped flowers, or you can choose a blend like ‘Sunrise‘ with pink, purple, blue, and white blooms in various patterns.

Morning glories are aggressive or considered invasive in some areas, so check your local regulations before planting these seeds. They are sensitive to root disturbance and perform best when sown outside. However, you can start them indoors 4 to 6 weeks before the last frost if you sow in biodegradable pots that can be directly planted in the ground to avoid handling the roots.

Black-Eyed Susan

For those who prefer native flowers, black-eyed Susan is a great seed to start in March. The sunny yellow flowers with their classic black centers are instantly recognizable, not only by gardeners but also by pollinators. They attract bees and butterflies during their flowering period, and the winter seed cones supply food for birds as well.

Start your seeds indoors 8 to 10 weeks before your average last frost date. While you can also direct sow outdoors, your black-eyed Susan may bloom in the first year if you sow indoors early enough.

Dianthus

If you want to start your cut flower garden from seed this March, dianthus is a good choice. The many species in this genus are known for their intricate flowers that last long in a vase. They are a staple in cottage gardens, but their variety means they’ll suit almost any garden design.

Dianthus seeds should be started 8 to 10 weeks before your average last frost date. They don’t always flower in the first year, depending on what you’re growing, but they are well worth the wait.

Shasta Daisy

The Shasta daisy is one of the most classic garden perennials you can grow. The bright white blooms with golden centers are instantly recognizable and look amazing when planted en masse. These perennials are also easy to grow from seed and attract pollinators to your garden beds.

Start seeds indoors in March, 6 to 8 weeks before your average last frost date, sprinkling them on the surface of your seed starting mix. They should emerge in 10 to 15 days and will be ready to transplant after all risk of frost has passed.