By Mickey Scullard, Master Gardener
Spring arrives in Minnesota at different times, with bouts of snow and cold temperatures contrasted with tantalizing peeks of the warmer weather to come. Pop-up garden centers appear in parking lots and garden centers ramp up advertising. Tired of the white and bland browns and grays, people flock to these sites to snap up green plants promising bright colors and fresh produce. This is the best time of the year for many gardeners with the potential for growing tried and true varieties and experimenting with the newest purple vegetable or unusually colored variety of zinnias.
To get the most out of Minnesota’s short growing season, it is important to understand when you can safely plant. We use the USDA Plant Hardiness Zone as a guide and the average last frost date. In Dakota County, we are considered Zone 4b and the average last frost date is mid-May (Midwest Regional Climate Center), although there is some data suggesting end of April is becoming more common. Remember these are averages and it is Minnesota, so you do need to stay vigilant to overnight temperature drops throughout the month of May.
Why is this important? Plants need the right conditions to grow and temperatures are a critical factor. Some seeds won’t sprout if the soil is too cold and may rot in the ground if it is too wet. Plants like tomatoes may survive but not thrive until temperatures are above 50 degrees at night and may need special protection such as water walls, cold frames, or cloches/bells (Extending the Growing Season). You may also have to cover plants that are sensitive to the cold when night temperatures drop below 32 degrees F. There are, however, a number of plants that prefer the cooler temperatures and in fact, thrive in our cool spring temperatures. This article won’t go into the soil preparation other than to note that you may need to wait if the soil is too wet as seeds may rot and not sprout.
Vegetables that love cool temperatures include many leafy greens (also very good for you!) such as spinach, leaf and head lettuces, endive, kale, and collard greens. You can direct seed all of these vegetables directly into the soil in mid-April. Spinach and the lettuces hate heat and will ‘bolt’ in June, July, and August, which means they grow a big seed head stalk and taste very bitter. You can grow a second crop in late summer/early fall when temperatures are lower again. Kale and collard greens will not only grow and be edible all summer, they will last through early frosts in the fall.
Other seeds you can sow in mid-April include beets, carrots, onions, parsley, peas, radishes and turnips. Additional vegetables you can plant in mid-April are broccoli, brussels sprouts, cabbage, cauliflower, and onion transplants or sets, but because they need a longer growing season than Minnesota offers, you need to start them indoors (or purchase plants) to transplant. Cabbage has both early and late varieties. The early variety can actually be planted in early April. Perennial vegetables, the plants that come back every year, that you can safely plant in mid-April are asparagus, horseradish, and rhubarb. Potatoes can also be planted in mid to late April into May, depending on the variety. Once you have all your April vegetables planted, you can add swiss chard, cucumbers, and parsnips to your garden in early May.
Don’t have time to get your seeds or transplants planted in April or early May? That’s okay. Most vegetables can be planted with good results through mid-June (except, as noted above, plants like spinach and lettuces). For a list of best planting times for these and other vegetables in Minnesota, the University of Minnesota Extension’s Planting the Vegetable Garden provides a chart under the “When to Plant Outside” heading. For more information on a particular vegetable, just type Growing (insert plant name here) in Minnesota into the search box.
So, if you are a gardener who is anxious to get started, try some of these vegetables and get your hands dirty!