27 Best Seeds to Start Indoors in Early Spring

Starting seeds indoors is essential for regions with short growing seasons and helpful for any gardener seeking to get a head start on spring’s abundance. After working on over 15 different organic farms across the United States, I know firsthand how important timing is for indoor seed starting. Spring sowing in a greenhouse or under grow lights can help you establish super strong seedlings that yield earlier and more abundantly compared to direct sown plants.

While warmer climates may have no problem sowing outdoors in early spring, zones 7 and cooler typically need to start a lot of their crops indoors to ensure robust transplants by the time the weather settles. This can save you a lot of time and money because you don’t have to rely on nursery seedlings and can extend your season so you can start harvesting fresh food earlier in the spring. 

To get indoor seed starting right, you must become a master garden planner! Don’t worry, this is easier than it sounds. It only requires simple math and a calendar. Timing is key, and I’ve got all the pro-farmer secrets to help you choose the right crops for indoor sowing and seed them at the right time to ensure maximum success! Let’s dig in!

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Plan Ahead and Know Your Dates

For most vegetables and flowers, sowing indoors 4-10 weeks before transplanting ensures they are the perfect size to transition into the garden when the weather has settled. The most common mistakes for spring gardeners are sowing too early or too late. 

If you plant seeds indoors too soon, they may become rootbound and leggy, overgrowing their containers before it’s warm enough to transplant them into the garden. This is especially common when planting tomatoes or squash too early. The oversized seedlings grow too large in their pots and sometimes have trouble transitioning into garden beds without succumbing to transplant shock.

On the other hand, if you sow too late, you miss a crucial window of opportunity that may reduce your overall growing season. This is particularly problematic for northern growers with short seasons. For example, if you garden in zone 5 and you forget to start peppers until May, the plants may not have enough time to fully ripen their fruits at the end of the summer. 

Personally, I like to create a mini spreadsheet or garden calendar to keep track of all this information for future years. The simplest way to start is with a chart that has 6 columns:

1. Crop Type
2. Variety
3. Days to Maturity
4. Recommended Seeding Before Last Frost
5. Indoor Seeding Date
6. Transplanting Date

This is exactly the system I used as a professional farmer to ensure that the greenhouse flowed perfectly with the season. Even if you only have a small windowsill or grow light setup, this planning process will make it much easier to track your indoor sowing schedule and take note of what works (or doesn’t work) for next year.

What Seeds Should You Start Indoors in Spring?

Some crops are best suited to indoor seed-starting, while others are best direct sown. Generally, long-season crops (with a high number of days to maturity) are sown indoors in early spring, while root crops need to be directly sown in the garden. Most indoor seed starting begins around 8-10 weeks before your last frost date in the spring. 

The earliest indoor seeding usually includes leeks, onions, celery, parsley, and some brassicas. As the last frost date gets closer, warm-weather crops like tomatoes and peppers are typically seeded indoors six to eight weeks before the frost date. You don’t want to start zucchini, winter squash, or cucumbers indoors until just one to two weeks before the estimated last spring frost.

16 Early Spring Vegetables for Indoor Sowing

Before you start indoor sowing, be sure to invest in a quality soil thermometer to monitor the soil temperature. If you don’t have a greenhouse or bright south-facing window, grow lights are super helpful for establishing strong seedlings.

1. Leeks

Notoriously cold-hardy and slow-growing, leeks are one of the first seeds you can sow indoors in open flats or cell trays. It’s recommended that most varieties get a head start eight to ten weeks before the last frost date. I like to broadcast sow leeks in shallow open flats at a depth of ¼” and covered with a light dusting of soil. 

After they emerge in 7-14 days, you can thin them to about one inch apart. When they reach six inches tall, it’s helpful to give them a haircut to encourage thicker shanks. Cut back about half of the tops and allow them to mature in the container to about pencil thickness. When it’s time to transplant around your last frost date, gently lift a handful of leeks from the soil and shake some of the dirt from their roots. Soak them in a water solution to easily separate the roots and plant deeply to promote more blanched stalks. 

Alternatively, you can sow leek seeds in groups of two to three in small cell plug trays and transplant them in bundles. Selectively harvest by holding the base of the others in place while you cut the largest ones away first. 

2. Onions

Most varieties of sweet onions and storage onions take up to 100 days to mature. If you start them indoors in early spring (about eight to ten weeks before your last frost), you can enjoy spring onions by May or June. I like to start onion seeds in the same way as leeks. Broadcast into open flats or sow in cell plug trays in bundles of two or three. Plant the seeds ¼” deep but do not cover with too much soil. Continuous moisture and room temperature will ensure even germination!

When the baby onions reach five to six inches tall, you can snip off the upper few inches to encourage larger bulb development. The clippings taste like yummy chives, so don’t throw them out! When plants are about pencil-thick, transplant them two to four inches apart, depending on variety and the desired size.

Before sowing onions, be sure you select the right type of onion for your region. This allium forms bulbs based on the length of daylight they’re exposed to. Short-day onions are best for the south, while long-day onions are better for the north. Some day-neutral onions are now available, which will form bulbs regardless of the day length.  

3. Celeriac

The strange and enticing celeriac, or celery root, plant requires an early start in protected conditions. Celeriac has a uniquely potato-like texture and cozy chicken-soup flavor, perfect for roasts and soups.

While we mostly think of this alien bulbous root vegetable as a fall crop, it needs to get started in the spring. This slow-grower is best sown 10 to 12 weeks before the last frost. It’s very important to start celeriac indoors because early exposure to temperatures under 50°F (10°C) can cause premature bolting. 

Seed your celeriac and celery indoors at the same time, under the same conditions. A heating mat can help keep the soil temperature around 70-75°F (21-27°C) for more rapid germination. The tiny seeds should only be planted about ⅛” deep and barely dusted with soil. Keep them consistently moist for two to three weeks while you patiently wait for germination.

4. Celery

This parsley relative is even more finicky than its celeriac cousin. I’ve never had any success starting celery outdoors because the seedlings are incredibly sensitive to any fluctuation in moisture or temperature. If you don’t keep them consistently wet, they won’t germinate at all. If you expose them to cool temperatures below 55°F (13°C), they will prematurely bolt and never form those crispy stalks you crave for summer dip boards. 

Sow celery seeds 10-12 weeks before your transplant date, which should be one to two weeks after the estimated last frost once the weather is reliably warm. The key to celery is “slow and steady.”

Sow the seeds in a reliably warm space like your greenhouse or grow light setup and never let them dry out. Don’t expose them to huge shifts in temperature. When hardening off, don’t put them in the cold weather. Instead, gradually reduce watering over the course of a week and then transplant under protection using a row cover or cold frame. 

5. Corn Salad/Mache

These cold-hardy greens got their name because they grew as weedy greens in winter corn fields. Mâche is remarkably cold-hardy and can often be direct-sown in the early spring in many climates. But if you still have snow on the ground, this early crop also benefits from a head start inside.

Seed mâche indoors in an unheated space up to 10 weeks before your last frost date and transplant outdoors three to six weeks before the last frost. However, be sure the seeds aren’t exposed to too much warmth. Temperatures above 70°F (21°C) will cause the seed to go dormant. This is a true cold-weather winter hardy crop.

As long as it has consistent moisture, mâche will perform very well in the cold. Seeds germinate slowly in 10-14 days and happily reach transplantable size in a cold greenhouse or sunroom. The chilly nights of early spring yield extra sweet, tender greens that give spinach a run for its money. 

6. Okra

This Southern classic isn’t only for warm climates! You can grow okra in northern zones as long as you start early and provide continuously warm soil. Sow okra seeds in pots or plug trays four to five weeks before the last frost date. A heating mat is recommended to keep the soil above 80°F (27°C) for fast, even germination. 

The seeds should be pressed into the soil about ½” deep and thinned to 1 plant per plug or cell. Once nights are warm enough, transplant okra into the garden under row cover. The delicious pods will begin developing in a couple months. Harvest them when they reach three to four inches long to avoid toughness. 

7. Parsley

Parsley germinates incredibly slowly, but it produces all summer long and well into the winter, so patience certainly pays off. Seed parsley 8-10 weeks before the last frost in one inch cell trays. Water consistently and keep trays at a steady 65-70°F (18-21°C) under grow lights or on a windowsill. 

Be very, very patient, as the seeds can take at least three weeks to germinate and sometimes up to 30 days. Once they finally sprout, allow the parsley to do its own thing until it reaches five to six tall and transplant into the garden a week or so before the expected last frost. Parsley seedlings are fairly cold-hardy as long as they are properly hardened off.

8. Peas

Snow peas and sugar snap peas are lovely early spring crops. They thrive in the cool weather and shy away from the hot sun. If you start peas in cell trays, you can transplant them extra early. However, direct sowing is just as feasible as soon as the ground is workable.

Plant pea seeds at a depth that is twice their largest dimension. I like to sow one to two peas per plug in 120-cell trays and cover with at least ½” of soil. They don’t need much more than consistent water and light. When they reach three to five inches tall, transplant in the ground next to a net or chicken wire trellis. Always install your trellis before transplanting the peas.

Plant plugs just two to three inches apart and train them upward by leaning the baby vines against the trellis. Their tendrils are like little vine arms and will naturally grab onto the trellis so they can grow in a tidy, upright fashion that makes harvesting far more enjoyable. 

9. Bell Peppers

One of the biggest problems cool-climate growers face is having enough heat days to fully ripen their peppers. In areas with short growing seasons, it is beneficial to start peppers early so they can take off as soon as the weather warms. If you don’t give the seeds a head start, you may reach the end of summer with only green peppers.

First, pick varieties suited to your climate. Northern growers may choose miniature bell peppers or thinner sweet frying peppers like ‘Jimmy Nardello.’ Sow pepper seeds shallowly in large cell trays about six to eight weeks before the last frost date. 

Place flats on germination heating mats and maintain soil temperatures between 80 and 90°F (27-32°C). Warmth is crucial for these South American plants! Peppers naturally germinate quite slowly, but cool soils will slow them down even more. The warmer, the better! 

Grow pepper seedlings in full sunlight at ambient temperatures around 70°F (21°C) or room temperature during the day and 60°F (16°C) at night. When the plants develop their first true leaves, you can strategically expose them to some cold, around 55°F (13°C), for three to four weeks to increase the amount of fruits later on. If this is too complicated, simply grow the baby peppers in the warmest, sunniest window you have and transplant outdoors once the risk of frost has passed.

10. Hot Peppers

Spicy peppers have almost the same growing requirements as sweet peppers. They should be started indoors around eight weeks before the last frost date. Again, full sunlight and warm soil are essential; you don’t want weak, leggy pepper plants. I always save my heating mats and best grow light positioning for peppers and tomatoes in the early spring, then make space for melons and cucumbers in late spring.

11. Kale

Kale can be sown indoors quite early in the spring because hardened seedlings have no problem facing chilly nights before the last frost date arrives. I like to plant kale about six to eight weeks before the estimated spring frost date, around February or March. This ensures the plants are in the ground and prolifically producing throughout spring before the heat of summer. For full-season production, choose bolt-resistant varieties that can yield in higher temperatures.

Although kale is very cold-hardy, the seedlings still require warmth to germinate and get established. Sow one to two seeds per cell about ¼” deep in plug trays. Air temperatures around 60°F (16°C) and soil temperature around 75°F (24°C) are ideal for quick germination. Once the seeds sprout, cooler growing temperatures between 55-70°F (13-21°C) are perfect for producing an abundance of greens. 

Choose varieties like ‘Black Magic’ or ‘Red Russian’ for a unique deviation from regular ole’ green kale. Plant under row fabric to protect from early emerging flea beetles.

12. Cauliflower

The rest of the early spring sowing list is all brassicas, including cauliflower. Brassicas or cole crops are grown almost exactly the same in my greenhouse and garden. They require very similar soil, planting, light, moisture, temperature, and even spacing in the garden. Even the cotyledons and young seedlings look strikingly similar, so labeling is a must!

As a general rule of thumb, sow your first round of brassicas four to six weeks before the last frost. The tiny round seeds should be planted about ¼” deep in a well-drained seed starting blend. Gently dust over the top, but avoid burying too deep. Water consistently and thin to one seed per cell when they emerge. 

Seedlings will be ready to transplant in four to five weeks when they have several sets of true leaves and the roots have fully filled out the plug tray. Take care not to leave your brassicas sitting in containers for too long. 

Cauliflower especially benefits from an earlier planting because rootbound seedlings have trouble transitioning into the soil and may suffer from transplant shock. Be sure to gradually harden them off by slowly exposing them to colder nights on a protected patio or porch. To shortcut the hardening-off process, try winter sowing.

13. Broccoli

Follow the same protocol for cauliflower and ensure that you choose the right broccoli variety for your region and the seasonality. Early spring and fall broccolis are adapted to cooler weather, while summer cultivars are bred specifically for bolt-resistance and reliable production in southern climates.

If you have had trouble getting broccoli to “head up” in the past, consider growing a broccolini or sprouting broccoli variety that produces an abundance of side shoots throughout the season. Personally, I think sprouting broccoli is tastier, more tender, and easier to cook with. Instead of harvesting just one head, the plant will yield continuously.

14. Brussels Sprouts

Start Brussels sprouts four to six weeks before your last frost date and transplant out when the soil is workable. For some reason, brussels sprouts tend to be magnets for early flea beetles and aphids. Perhaps it is because natural predators aren’t yet active, and the plants have a strong cruciferous smell. I always cover the young plants with a low tunnel of row fabric to physically exclude the pests. 

15. Cabbage

From Napa to red leaf to storage types to Savoy, there are so many different varieties of cabbage for different uses. Napa cabbage is best for kimchi and fermentation, while dense storage types are great for sauerkraut. Savoy cabbage is lighter and fluffier, ideal for coleslaws. Bright red cabbages add a fun flair to summer dishes. 

No matter what type you choose, be sure to plant early and mid-season varieties about four to six weeks before the frost date. Sow in cell plugs about ¼” deep and follow the same protocol as  cauliflower, broccoli, and Brussels sprouts. Cabbage is a cool-weather crop that thrives best in early spring, so get the transplants in the ground as soon as the soil is workable and only occasional light frosts remain.

As a general rule of thumb, cabbage and other brassicas are best planted 12-18” apart in rows 18-36” apart. The plants can spread out quite wide, so avoid planting too close, or you may hinder them from producing full heads.

16. Collards

Collard greens are kale’s less popular cousin, but they are no less nutritious or delicious! Collards are easy to grow and more tolerant of warm weather than other brassicas. This is why they are so popular in the South!

Choose a slow-bolt variety and seed indoors four to six weeks before your frost date. Always thin to one plant per cell and gradually harden off to help them adjust to cold nights. Collards enjoy chilly weather but cannot withstand frosts in the early stages.

11 Flowers to Seed Indoors in Early Spring

While many flowers can be purchased from local nurseries in the spring, starting from seed allows you to explore a more expansive range of colors, shapes, and varieties that aren’t available in stores. You can also save a lot of money and enjoy blooms earlier in the season. Early spring flower seedlings typically do well in the same grow light setup as vegetables or in a warm, sunny greenhouse.

17. Asclepias spp. (Butterfly Weed)

Butterfly milkweed varieties are as beautiful as they are functional. The Asclepias genus includes over 200 species of native and exotic milkweed flowers that provide crucial nectar and host habitat for butterflies. Anyone who loves pollinators must grow a few species of Asclepias in their garden!

Most butterfly weed seeds can be sown up to 8-12 weeks before your frost-free date. Placing them in a substrate and putting it in the refrigerator for 2 months ahead of sowing gives them the cold, moist period they need to germinate. Depending on the variety, it takes 100 to 130 days to mature, so early seeding is helpful if you want to attract as many butterflies as possible when summer comes around.

These native plants can be sensitive to transplanting, so growing in biodegradable pots is ideal for reducing root disturbance. The taproots are particularly sensitive to becoming pot-bound, so ensure you transplant young.

18. Delphinium

These stunning long stalks of colorful flowers take a whopping 100-150 days to mature. Start seeds indoors in late winter or early spring about 10-16 weeks before the last frost date. Larger three to four inch pots are ideal for preventing root binding.

Give delphiniums a cold stratification period – like you would milkweed – for one to two weeks. Then very lightly cover the seed with soil, but do not plant too deep. Grow at 65-70°F (18-21°C) and avoid overwatering, as delphiniums struggle in soggy soil. Be sure to install a trellis support system before transplanting into the ground.

19. Foxglove

The vivid tubular flowers of foxgloves (Digitalis spp.) are as enticing to bees and hummingbirds as they are to cut flower growers! Whether you want to grow foxgloves for arrangements or ornamental beds, starting indoors will promote earlier development of the bell-shaped blooms. 

Pre-treat your seeds with cold stratification for two weeks. Sow seeds shallowly in cell trays about 10-12 weeks before your last frost date. Do not cover the seeds, as they need light to germinate. Instead, gently press them into the soil or dust with fine vermiculite to hold them in place. 

Misting or bottom watering is best to prevent the seeds from becoming displaced or disturbed during watering. About 15-20 days after seeding, foxgloves should develop their first true leaves and can be transplanted into larger containers. Do not transplant until hard frosts have passed.

20. Petunias

These popular annual flowers come in every color of the rainbow but have very little tolerance for frost. You can sow them indoors in early to mid-spring to help the tender plants develop in a protected environment. By the time frosts have passed, you will have strong seedlings to move into hanging baskets or container arrangements for earlier blooms.

Start petunia seeds eight to ten weeks before the last frost date in soil blocks or cell trays. The tiny seeds should be sown just ⅛” deep and thinned to one to two plants per cell. They take about 7-21 days to germinate and require consistent water and warmth.

21. Stock

Also known as Matthiola incana, these gorgeous elongated clusters of fluffy blooms are actually members of the Brassicaceae family, just like kale and cabbage. Stock is popular for floral arrangements and makes a gorgeous addition to annual flower beds. Start the seeds eight to ten weeks before the frost-free date, sowing ¼” deep and keeping the soil evenly moist at a temperature around 60-65°F (16-18°C). 

22. Sweet Pea

Unlike sugar snap peas, sweet peas are grown specifically for ornamental value and cannot be eaten. These climbing vines have pretty curling tendrils and dainty flowers that smell like honey or jasmine. They are available in a plethora of vibrant colors and benefit from early seeding, so you can enjoy the flowers throughout May and June. 

Sweet peas are cool-season flowers that take 70-90 days to mature. You can start indoors 4-5 weeks before transplanting out. Scarify the seeds with fine sandpaper, and soak them for a couple of hours before planting. Since the seedlings can survive light frost, it’s OK to transplant several weeks before your last frost date as long as the soil is workable. 

Pinch sweet pea seedlings when they reach six to eight inches tall to encourage them to branch out and produce more flowers. Be sure to install a trellis in advance or grow sweet peas along a fence line.

23. Snapdragon

Snapdragons are magical-looking flowers with long splays of symmetrical, tubular blossoms that almost look like lips. Only large bees can pry open the blossoms to get the nectar inside, and the flowers “snap” closed behind the bee to encourage maximum pollination. These short-lived perennials are best seeded indoors 10-12 weeks before your frost-free date. This allows the plants to develop a robust root system.

Cold stratification is recommended for these unique flower seeds. Before planting, place them in the refrigerator for 1-2 weeks. Sow the seeds very shallowly by thinly pressing into the soil. Do not use bottom heating, as snapdragons prefer cooler soil. Wait 8-14 days for emergence and provide consistent moisture without oversaturating.

24. Rudbeckia (Black Eyed Susan)

Black-eyed Susans are a popular native perennial that can easily be propagated by seed. Start with a cold stratification period of two to three months. Then soak the seeds in warm water overnight and then sow indoors about six weeks before your last frost and leave the seeds uncovered. Bottom watering or misting helps keep the soil moist without dislodging the young seedlings.

Transplant around the last frost date. Starting this perennial from seed provides an abundance of young plants for very cheap. Don’t worry if your plants lack flowers in the first year. Many varieties are biennial and won’t produce flowers until their second season.

25. Verbena

The delicious lemony smell of verbena adds a delightful ambiance to your home and garden. Cold stratify your seeds for four weeks. This pretty herb can be sown indoors eight to ten weeks before your last frost date, usually in February or March. Wait to transplant verbena until the danger of frost has passed. This tender perennial is slow to germinate and sensitive to soggy soils, so keep the soil a bit drier than your other seeds.

26. Yarrow

Yarrow is my favorite perennial flower because it is native to the U.S., super easy to grow, drought tolerant, and it attracts a huge diversity of beneficial insects. The seeds are easy to germinate in trays in a poorer quality soil mix without much compost. I’ve learned not to grow yarrow in super-rich soil because it makes the stems weaker and the flowers less fragrant.

Provide your seeds with cold stratification for one month. Seed indoors eight to ten weeks before the last frost. Avoid covering the seeds. As you can tell, many flower varieties (especially native wildflowers) require light to germinate. You can dust with a very thin layer of vermiculite to help retain moisture. Mist or bottom water for three to five weeks until the seedlings are established; then, you can water from overhead. Full sunlight is essential for strong plants.

27. Pansies 

Violas or pansies do well when sown indoors 8-12 weeks before your estimated frost-free date. Cold stratify them for two weeks first. These edible flowers are sometimes called “Johnny jump-ups” because they have very quick growth in the spring. An indoor start will ensure you have the earliest flowers to brighten up your spring garden! The young plants will also tolerate a light frost if properly hardened off. These sweet flowers are frost-hardy and can also be sown directly outdoors.