When to Start Seeds in Zone 6

Starting seeds allows you to grow a wide variety of crops and get a jumpstart on your growing season. Join former farmer Briana Yablonski as she shares when to start seeds in zone six.

A vibrant summer day at Smale Riverfront Park in Cincinnati, Ohio. Lush wildflowers in shades of red, purple, and yellow line a sidewalk along the Ohio River. In the distance, the John A. Roebling Suspension Bridge stretches majestically across the water, its steel towers reaching towards a clear blue sky.


Starting seeds at home allows you to grow a wider variety of plants than you would if you only purchased plants from a nursery. Plus, there’s nothing like filling your home with tender green plants when it’s still cold and dreary outside!

Since different plants have varying growth rates and temperature requirements, each type of seed has an ideal seeding time. I’ll cover how to determine when to start your seeds in zone six so you’ll have mature seedlings ready to plant out when the proper weather arrives.

Where Is Zone Six?

A vibrant spring scene captured in Eden Park, Cincinnati. Blooming flowers in shades of pink line the edge of a serene pond, reflecting the colors of the cloudy sky above. Lush green trees with budding leaves provide a backdrop to the colorful display.
Zone six now includes cities like Hartford, Detroit, Chicago, and Denver.

The recent changes to the USDA Plant Hardiness Zone Map have slightly adjusted zone six’s boundaries. This growing zone now spans across much of the central United States as well as into parts of New England and the Pacific Northwest.

Some cities located in this zone include Hartford, Detroit, Chicago, Topeka, Denver, Cincinnati, and Pittsburgh.

What Is the Zone Six Climate?

This image captures the winding paths of a circular stone labyrinth in Smale Riverfront Park, Cincinnati. Lush green grass borders the labyrinth, and in the distance, the iconic towers of the Queen City skyline rise above the Ohio River.
The climate varies, but all areas share -10 to 0°F (-23 to -18°C) average low temperatures.

Since zone six spans across much of the country, the climate varies throughout its range. Some areas experience dry summers coupled with heavy winter snowfalls. Other areas deal with humid summers dotted with thunderstorms and moderately wet winters.

Despite these differences, all areas share one factor: their average low temperature. In an average year, all locations experience a low temperature between -10 to 0°F (-23 to -18°C). These extreme lows can kill unprotected, cold-hardy annuals and perennials and cause the ground to freeze.

Due to the cold winter temperatures zone six experiences, the air and ground are slow to warm up in the spring. While the last spring frost varies by year and exact location, it typically arrives between mid-April and mid-May. The first fall frost often occurs sometime in October.

How to Determine Seed-Starting Dates

A tiny curly kale seedling emerging from moist soil with two delicate cotyledons, fully unfurled. Their edges are slightly ruffled, hinting at the characteristic curls that will develop on the mature leaves. A tiny true leaf is also visible, emerging from the center of the cotyledons.
Start seeds based on your area’s last frost date for successful spring planting.

One of the most intimidating parts of starting seeds is knowing when to plant them! If you start them too soon, you’ll end up with mature seedlings ready to plant when the ground is still frozen. And if you start them too late, the plants aren’t mature before cold weather arrives in the fall.

Determine Your Frost Date

Fortunately, there’s an easy way to determine when to start your seeds. When it comes to starting seeds in spring, note your average last spring frost date, which occurs sometime in late April or early May. You can look up the last frost date in your area to obtain a more accurate date.

With your last frost date in hand, determine when you want to transplant seedlings into your garden. You can plant frost-tolerant crops like cabbage, kale, and viola a few weeks before the predicted last frost. If temperatures dip below 28°F (-2°C), just cover the tender plants with row cover to protect them from damaging cold. Since summer crops like tomatoes, zinnias, and cucumbers prefer warm soil and air, wait until a few weeks after the last frost to transplant.

After determining when you want to plant your home-grown seedlings outdoors, figure out when to plant your seeds. Most seeds take four to ten weeks to grow from seed to seedling as long as you provide them with the proper temperature, light, water, and soil mix. If you’re unsure how long a specific seed takes to grow into a seedling, look at the seed packet.  For example, the ‘Celebration’ Swiss chard seed packet tells you to start seeds indoors four to six weeks before transplanting outdoors.

Plan for Fall

While many gardeners focus on their spring and summer gardens, don’t forget about fall plants! Growing a second round of cool-weather plants in the fall allows you to enjoy a second harvest and experience how crops become sweeter once cold temperatures arrive. The goal with fall gardening is to get transplants in the ground so they fully mature before the first ten-hour day arrives. In zone six, this means starting seeds for fall crops in the summer.

When to Start Seeds

You’re welcome to use the above information to calculate when to sow your seeds. However, if you’d like to skip some math, you can use the tables below as guides.

Vegetable and Flower Seeds for Spring Planting

A close-up of a cluster of amaranth seeds on a branch, bathed in warm sunlight. The seeds are mostly brown, but some are a deep purple-pink with most of the seeds still attached to the stem, while others have fallen off. Some seeds are plump and smooth, while others are slightly wrinkled and textured.
Seed starting dates vary, with mid-April to mid-May last frost dates.

The following recommended seed starting dates will provide you with frost-tolerant seedlings that are ready to transplant outdoors near the last frost date. Since tender crops like basil, tomatoes, peppers, marigolds, and amaranth can’t handle cold, starting seeds at the following dates ensures the seedlings aren’t mature until a few weeks after the last frost date.

Since zone six encompasses such a large area, the last frost date varies by month depending on the specific location. If your average last frost date occurs in mid-April, start your seeds near the earlier end of my suggested planting dates. And if the last frost arrives in mid-May, start your seeds near the end of the date range.

Note that this is just an estimate. To ensure the most accurate frost date, consult the National Gardening Association’s Frost Date Calculator. This gives you the best-estimated date for your individual zip code. From there, follow the instructions on your seed packet to determine when to begin sowing seeds.

Amaranth March 15 to May 1
Basil March 15 to April 15
Broccoli March 1 to April 1
Cabbage March 1 to April 15
Calendula March 1 to April 1
Cauliflower March 1 to April 15
Celery February 1 to March 15
Celosia March 1 to April 15
Chard February 15 to April 1
Collards February 15 to April 1
Cosmos March 1 to April 15
Cucumber April 1 to May 15
Eggplant March 15 to May 1
Fennel February 15 to March 15
Kale February 15 to March 15
Lettuce February 15 to April 15
Marigold March 1 to April 15
Melons April 1 to May 15
Okra April 1 to May 1
Parsley February 1 to March 15
Peppers March 1 to April 1
Rudbeckia February 15 to April 1
Snapdragon February 15 to April 1
Strawflower March 1 to April 1
Summer Squash April 1 to May 15
Tomatoes March 1 to April 15
Zinnias April 1 to May 1

When to Direct Seed Flower and Vegetable Seeds Outdoors in the Spring

Rows of vibrant green carrot tops stand tall in a freshly turned bed of dark, crumbly soil. The air hums with the promise of harvest, as sturdy stalks reach for the sun. The soil, devoid of weeds, whispers of careful tending, promising plump orange treasures lurking beneath its surface.
Root vegetables and baby greens are best directly sown, with colder soil potentially delaying germination.

While starting seeds indoors helps you achieve an earlier harvest date, you can’t transplant all crops. Root vegetables and baby greens grow best when you direct sow them in your garden. Since colder soil temperatures lead to slower germination, planting seeds on the earlier end of the following date ranges results in delayed germination. However, as long as the seeds don’t rot, they’ll eventually germinate.

Since many direct seeded crops lend themself well to succession planting, don’t be afraid to plant seeds more than once. I like to direct sow rounds of baby greens and roots about every two to three weeks in the spring, so I end up with an extended harvest.

Arugula April 1 to June 1
Beans May 1 to August 1
Beets April 1 to June 1
Bok choy April 1 to June 1
Carrots April 1 to June 1
Cosmos April 1 to June 1
Kale April 1 to June 1
Peas March 15 to June 1
Poppies March 15 to April 15
Radishes April 1 to June 1
Spinach April 1 to June 1
Turnips April 1 to June 1

Starting Seeds for Fall Planting

A close-up of a young cauliflower seedling growing in a small plastic pot. The seedling has two bright green cotyledons, or seed leaves, and a pair of true leaves emerging. The moist soil is dark and rich, and the pot is placed on a light-colored surface.
Many crops stop producing by October’s first fall frost; others persist until shorter daylight hours.

The first fall frost arrives sometime in October in zone six, which means the end of basil, zinnias, peppers, and more. However, many crops withstand colder temperatures and grow until daylight falls below ten hours. The trick is to start your seeds early enough that the plants mature by mid-fall.

Bok choy June 15 to August 1
Broccoli June 15 to August 1
Cabbage June 1 to July 15
Cauliflower June 1 to July 15
Chard June 1 to July 15
Collards June 1 to July 15
Fennel June 1 to July 15
Kale June 15 to August 1
Lettuce July 15 to August 15
Radicchio June 15 to July 15
Spinach August 1 to September 1

Final Thoughts

Now that you know when to start seeds, it’s time to ensure you have all you need to get started. A well-draining soil mix, seed starting trays, a heating mat, and a grow light are some of my must-have items for indoor seed starting. With the right tools and information at your disposal, you can fill your garden with home-grown seedlings this year.

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A red Gladiolus bloom is covered in a thin layer of frost.

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