When to Start Seeds in Zone 4

If you live in USDA zone 4, long, cold winters can make growing many common vegetables and flowers challenging. Rather than waiting until the weather warms up to plant seeds outdoors, you can get a jump start on your growing season by starting seeds indoors in zone 4. Not only does this help you get plants in the ground earlier in the year, but it fills your home with green life while it’s still cold outside.

But it’s not recommended to just plant seeds when you feel like it and hope for the best! While this may work out, it can also result in rootbound seedlings and plants that don’t mature in time. A better option is to calculate the optimum sowing dates for each seed and start your seeds accordingly.

I’ll cover factors to consider when determining when to start seeds in zone 4 and provide the ideal times to plant various seeds.

Where Is Zone 4?

Zone 4 includes some of the coldest areas of the continental United States. After the recent changes to the USDA Plant Hardiness Zone Map, this zone now includes much of the upper Midwest and Central Plains, as well as portions of New England and the Rocky Mountains.

Bismark, Duluth, Eau Claire, Lake Placid, and Cut Bank are all located in zone 4.

What Is the Climate in Zone 4?

Gardeners in the far north are accustomed to long, frigid winters. Temperatures drop as low as -20°F to -30°F during an average year, and average daily high temperatures hover around freezing during the year’s coldest months.

Summertime highs hover in the 70s and low 80s, meaning this isn’t a climate for heat-loving crops like okra and sweet potatoes. However, kale, lettuce, and radishes can grow well in the summer. If you start seeds indoors in the spring, warm-season crops like peppers, tomatoes, melons, and squash still have time to mature outdoors in zone 4. Consider selecting some varieties that can tolerate cooler conditions, like ‘Glacier’ tomatoes.

How to Determine When to Start Seeds

Learning when to start seeds in zone 4 is important for two main reasons: you don’t want to start too early or plant too late.

If you start the seeds too early in the year, they’ll outgrow their seedling containers before it’s warm enough to plant them outdoors. But if you start them too late in the year, they may not mature before fall frosts and short days arrive.

So, how do you know the right time to start seeds? By using historical data as your guide.

First, learn your area’s average last spring frost date. Although the exact date varies by location, it occurs sometime between mid-May and mid-June in zone 4. This date determines when it’s safe to plant seedlings outdoors in the spring and, thus, when you should start seeds.

Note that this is just an estimate. To ensure the most accurate frost date, consult the National Gardening Association’s Frost Date Calculator. This will give 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.

Spring Example

Let’s look at ‘Di Cicco’ broccoli as an example. Since broccoli seedlings can withstand light frosts (especially when you protect them with a layer of row cover), you can plant them right around your last frost date. For this example, let’s say that’s June 1. The seed packet states that you should start seeds four to six weeks before transplanting. Counting back from June 1 means planting the seeds between April 23 and May 7.

Fall Example

You’ll do things a bit differently when it comes to fall plantings. Rather than using the last spring frost date as a guide, you’ll look at the first fall frost date, which occurs from mid-September to mid-October.

Let’s revisit the ‘Di Cicco’ broccoli I mentioned above. When you look at the seed packet, you’ll see it instructs you to start seeds 12 weeks before your average first fall frost date. If you expect your first frost on October 1, you should start ‘Di Cicco’ seeds around July 9.

When to Start Seeds in Zone 4

While you can use average frost dates and plant information to determine when to start your seeds, I’ve compiled some tables to save you time.

When to Start Vegetable and Flower Seeds for Spring Planting

As I explained above, the average last spring frost date determines the best time to start your seeds indoors. Since cold tolerance and plant growth rate vary between plants, the ideal seed starting date also changes based on the species.

While all locations in zone 4 share a similar average low temperature, they have varying average last frost dates. Therefore, I’ve included a range of seed starting dates that work well for different locations throughout zone 4.

As always, check your annual last frost date before selecting your exact planting time so you don’t inadvertently start your seeds a bit too early! This is a crucial step for success.

Once your seedlings are ready to plant outdoors, spend at least a week hardening them off to the outdoor conditions in gradually increasing lengths. This will help them adjust to their new home and limit stress.

Chart: Zone 4 Indoor Seed Starting Dates

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

Since zone 4 has such a short growing season, I recommend transplanting as many crops as you can. However, you’ll still have to direct-sow some roots and greens. The following dates are the average times to put your first planting of seeds in the ground. As before, check your final frost date to ensure you don’t plant when frost is still a risk in your local area!

Chart: Zone 4 Direct Sowing Dates

When to Start Seeds for Fall Planting

Since cold temperatures arrive early in the fall, you must start fall seeds early. Starting seeds during the following dates will allow you to get seedlings in the ground so they have time to grow before the first fall frost.

Chart: Zone 4 Fall Seed Starting Dates

Final Thoughts

Just because zone 4 has a short growing season, it doesn’t mean you can’t have a bountiful garden! Starting seeds at the right time allows you to produce healthy transplants ready to plant just in time for vigorous growth and abundant harvests.