We are in that time of year when the snow has melted, the days are warmer, and the sun is higher in the sky, but the earth has not yet greened over. The grass is still dormant and yellowish. Buds are on the trees, but the landscape still looks raw with the mark of winter’s cold touch. The threat of frost is still real, and nature, wise with many years of experience, steps out gingerly into the new season.

It’s not the prettiest time of year in the Upper Midwest. While warmer places revel with riotous flowers, we wait patiently, content with a few brave crocuses.

My thoughts and eyes have turned to the modest garden plots in our small yard. We live in a townhouse and have a little space for gardening in a courtyard, along the front walk, and in the back. We inherited a garden when we moved here last summer, and if all goes well its hostas, morning glories, thyme, rosemary, hens and chicks, and other plants will come back. We added tulips and black-eyed susans last fall.

I have two regional gardening books to help me: Gardening in the Upper Midwest, by Leon C. Snyder (Univ. of Minnesota Press, 1978), borrowed from my parents; and The Minnesota Gardener’s Guide, by Melinda Myers (Cool Springs Press, 2001).

From these sources I’ve already learned that gardeners tell us a good deal about regional geography. They must be aware of their own climate and its suitability for various plants. For example, they need to know when to plant so that the frost does not kill new growth.

Here is what Leon Snyder writes about the Upper Midwestern climate:

“In the winter, the temperature can drop to -40? F or colder. In the summer, temperatures can climb to 100? F or higher. Not only does this area have extremes of temperature but it also has a fluctuating rainfall. Summer droughts are not uncommon. Generally, the rainfall decreases as one moves in a northwesterly direction. Average annual rainfall in our area ranges from about 28 inches in the southeast to about 16 inches in the northwest. Fortunately, most of this rainfall comes during the growing season.” (p. 3)

In her discussion of climate, Melinda Myers analyzes frost dates. The last spring frost is a crucial determinant of when a gardener can plant. The number of frost-free days (on average) is obtained by counting the number of days between the last spring frost and the first fall frost. “The frost-free season varies from 107 to 160 days in southern Minnesota,” Myers writes, “and from 90 to 120 days in the northern part of the state.”

That means the colder parts of northern Minnesota are only frost-free for one quarter to one third of the year–from early or mid-June to late August, according to the map in her book. Southern Minnesota, including the Twin Cities, is generally frost-free from early May to early October. No part of the state is frost-free, on average, more than half the year. Although a night that falls to 30? F might be followed only hours later by a high temperature in the 50’s or 60’s, the region is indeed cold. But we already knew that.

Next week: More on geography and gardening, including links to pretty maps.

This entry was posted on Saturday, April 9th, 2005 at 11:00 am and is filed under Gardening, Geography, Minnesota, Weather.