How to Extend Your Gardening Season in North Dakota (Yes, It’s Totally Possible!)

If you’re a gardener in North Dakota, you’ve probably looked out the window in March, longing to get your hands back in the soil. With our notoriously short growing season and frigid winters, it might feel like you only get a few good months to grow anything. But here’s the good news—you can grow more, for longer, with a few clever season extension strategies. 

Let’s dig into how you can make the most of your garden in Zones 3b to 4b, and maybe even enjoy fresh greens when there’s snow on the ground. 

Know Your Zone (And Your Daylight) 

North Dakota gardeners are mostly in USDA Zones 3b to 4b. That means your frost-free window is short. The average last frost dates range from May 9 in Grand Forks to May 17 in Minot. The average first frost dates range from September 17 in Minot to September 25 in Bismarck. But you can extend your growing season well beyond your average frost-free date using some of the relatively simple and cheap strategies described below. But freezing temperatures aren’t the only limitation we face when extending the growing season. Along with temperature, daylight plays a big role in plant growth. When we dip below 10 hours of daylight (around mid-November to early February), most plants stop actively growing. So the goal becomes either speeding things up before that point—or holding mature crops in place with a little protection. 

Cold-Hardy Vegetables Are Your Best Friends 

Extending your growing season begins not with putting up protective structures but with choosing cold-hardy plants that laugh in the face of frost. Focus on these veggies to grow into the colder seasons (early spring and late fall):  

Spinach – The undisputed king of cold-tolerant veggie. Spinach will stand unprotected all winter and resume growing in spring; allowing you to have garden-fresh spinach months early. To the right is a picture of overwintered spinach in my garden in mid March.  

It looks terrible, but there is still green beneath those dead leaves. A little clean-up and we are dining on spinach salads by late April. You can also start spinach inside in late February and plant it out, under cover, when the ground thaws. Spinach tends to bolt (go-to-seed) rather easily as the spring temperatures increase, so sow often, either inside or out.  

The trick to fall spinach is sowing early enough to allow the plants to get large enough to harvest before the daylight hours get too short to support continued growth. I find the first week in September, a time when most people are thinking of wrapping up the gardening season, is the best time to direct-seed spinach for a fall and winter harvest. The beautiful thing about spinach is that it gets sweeter as the days and nights get colder. That’s because the increased sugar content acts as a natural anti-freeze in cold-hardy plants. Your spinach may well freeze solid during those late fall and winter nights. Wait until the daytime temperatures get above freezing and the plants thaw before harvesting. A little added protection can extend the season even further. I’ve harvested spinach grown in my unheated high tunnel well into December. 

Kale – Tough as nails, with growth habits similar to spinach. Like spinach it tastes better after a cold snap. I prefer to start plants in plug trays and plant out under cover in early September for a fall harvest. Similarly, for spring I start the seedlings indoors in mid to late March. I acclimate my kale in the spring by hardening them off for three or four days; shuttling trays of kale inside at night and outside in morning once daytime temperatures reach above freezing. Once hardened off and soil thawed, they can go in the garden. They can stand up to a hard freeze, temperatures below 28°F for a few hours, but in my experience, seedlings have trouble recovering from extended periods below 25°F. For that reason, I will keep my spring kale covered until the nights are consistently above freezing, typically mid to late April. 

Lettuce – Loves cool temps and can handle frost unprotected. But if temperatures drop below 28°F they will require some protection. Like spinach I will direct sow my last lettuce crop in early to mid September so that it has time to mature before the days become too short. Because lettuce is not as cold-hardy as spinach it is generally done by Thanksgiving.  Where lettuce really excels is in the spring. I sow seeds in a small tray in late February, prick-out the seedlings at the cotyledon stage to cell trays a week or so after sowing and plant them into the high tunnel in mid to late March. I begin transplanting into garden beds, under cover, in late April.

Chard and Asian greens – Chard and Asian greens such as mizuna, bok choy, tatsoi, and others behave similar to lettuce and do well in cool temps. With just a little protection these greens can be set out in late April/early May. Asian greens will bolt and have to be taken out of the garden as summer heat progresses but are a great fall crop when direct sown in the last week of August or the first week in September. Chard on the other hand is a crop that you plant once and will keep producing into mid-fall. All of these greens can handle a light frost down to 32°F, but with protection can be maintained down to the mid-20s. 

Peas – Peas are a sweet cool season champ. They handle light frost but don’t do well if temperatures dip a few degrees below freezing. The two biggest challenges to planting early peas are:  

1. They are difficult to cover and trellis at the same time  

2. The strong, cold winds we experience in a North Dakota spring really beat-up tender young pea plants.  

I aim to sow my peas in cell trays around April 15th, begin hardening them off a week later and transplanting them the first week in May. I haven’t tried growing peas in the fall. 

Timing Is Everything: Planning & Germination 

Spring in North Dakota can be unpredictable. Watch your soil temperature, not just the calendar. The North Dakota Agricultural Weather Network is a great resource for finding the current soil temperature in your county. Once the top eight inches have thawed you can go ahead and transplant, but generally keep your transplants covered. Cold-hardy seeds germinate well in cooler soil, so don’t be afraid to plant early. If you want to get a jump on direct sowing in the spring, for example carrots, put down a layer of clear 6 mil plastic in the fall or just after the snow melts in the spring. The bright spring days will quickly warm the soil beneath the plastic. In the fall, aim to get seeds in the ground far enough ahead so plants are nearly mature by the time daylight drops off. After that, you’re not growing—you’re just preserving the harvest. 

Row cover: A Simple Way to Extend the Season (No Heated Greenhouse Required) 

You don’t need fancy equipment to stretch your growing window. One of the most effective, and surprisingly low-tech tools is row covers. Row covers are a lightweight spun fabric that protects against frost and wind. 

Protection from cold, drying winds is particularly important in the spring when setting out tender young seedlings. It tends to be less important in the fall when direct sown seedlings have grown up and acclimated to our North Dakota winds. I’d recommend against buying the thin, cheap row covers you find at Walmart, hardware stores and local nurseries. One strong North Dakota wind will reduce these to ghostly tatters in a day. Spend a little extra and purchase commercial grade row cover. These come in different weights, from 0.5 oz per square yard to 2 oz per square yard, that offer increasing degrees of protection. I prefer Agribon AG-50 that will provide frost protection down to 25°F. Although you can “float” row cover by laying the fabric directly on top of seedlings and mature plants, this does risk damaging the plants by allowing the leaves touching the fabric to freeze. It is best to support the row cover on 9-gauge chain link tension wire that you can find at the hardware store. Cut the wire into 76” hoops. Row covers are water and light permeable so you can water right through the fabric. The fabric slows evaporation by cutting down on drying winds and sunlight so you can get away with less watering.  Plants will also require less water as growth slows during the fall. Expect slower growth—or even a pause—once sunlight drops below that critical level of 10 hours of daylight in November. 

Step It Up with Unheated Structures 

Cold frames are an inexpensive way to give you a big jump on the growing season. My 2’x3’ cold frames are built entirely of scrap wood and reclaimed glass panels. The cold loving crops, like spinach starts, can be placed in these frames in mid-March when there is still snow on the ground. In fact, snow is actually a great insulator, so don’t remove it from around a cold frame. The biggest challenge with using a cold frame, and other season extending structures, is actually heat. On a sunny spring day, a cold frame can quickly heat up and cook those tender young starts. A notched stick is typically used to raise the north side of the glass panels and vent the accumulating heat. Another great advantage to using a cold frame in North Dakota is protection from cold, drying spring winds. Depending on the wind direction I may raise the glass and vent on the north, east or even west side of the cold frame to buffer the plants from the wind while allowing the heat to escape. Whenever possible though I will completely remove the glass panels and expose the plants to a little breeze; say less than 10 mph. This helps build sturdy plants that can stand up to inevitable North Dakota winds. Finally, if the nights are getting below 25°F, I will put row cover over the plants before closing up the cold frame in the evening and remove it the next morning. 

I’ve only just started using low tunnels to extend my warm season crops an extra couple of weeks. Low tunnels are created by placing 6 mil plastic over hoops of bent 10’ electrical conduit or even 1” PVC pipe and can be anywhere from 2’ to 4’ tall. A nice feature of low tunnels is that they can be built over existing crop beds to extend your harvest season. I used these over peppers and tomatillos last fall and was harvesting fruit until the final days of our local farmer’s market at the end of October. 

If you are willing to spend the money an unheated high tunnel (aka, polytunnel) will open a world of possibilities. A complete 14’x 20’ high tunnel kit will run about $2,500 but if you are willing to source your own material and bend your own pipe, you can cut that cost nearly in half. I built my 14’x32’ high tunnel for under $1,500 using the hoop bender and instructions from Johnny’s Selected Seed. There are things I would do differently, but it has served me well for the past 4 years. I plant out in my high tunnel with transplants of lettuce, arugula, and spinach in mid March for harvests in late April or early May. Since nights may still be getting down into the teens in March, I add extra layers of row cover and even low tunnels inside the high to retain the daytime heat. For example, on March 22 the low at my farm was 20°F but inside the high tunnel under a layer of AG-50 row cover and a low tunnel covered with plastic, my crops were a snug 39°F. Garden guru Eliot Coleman estimates that each layer of protection moves your growing zone up by about 1.5 zones. That means a gardener in Zone 3b could be gardening like someone in Zone 5 or even Zone 6 with the right setup. Similarly, I direct-seed spinach, arugula and mizuna in early September and harvest well into December. Like cold frames, the biggest challenge with a high tunnel is not protecting from the cold but dealing with heat. Even in January on a sunny day with snow on the ground and teens outside, it is not uncommon for the high tunnel to reach into the 70s. In addition to providing insulation, the reflected light from the snow will cause a high tunnel to heat up quickly. Because of this, as well as minimizing moisture and mold buildup, I will vent the tunnel even in the middle of winter. 

Get out and garden!  

We may live much of the year in the frozen north but with a few simple tools and techniques it is possible to enjoy garden-fresh produce well beyond the traditional gardening season. Start small with row covers over spinach seedlings in mid April and direct-seeded spinach in early September. As your confidence grows, expand to other cold-hardy greens and push the season. 

Recommended Reading 

If this topic has you fired up, check out Eliot Coleman’s books like The Winter Harvest Handbook and Four-Season Harvest, as well as The Winter Market Gardener by Jean-Martin Fortier and Catherine Sylvestre. They’re packed with knowledge and inspiration, especially for cold-climate growers.