This week I'd be remiss if I didn't extend some thoughts on the major season-end topic: putting the garden to bed for winter.
Those of you non-gardeners who have been faithfully following this column because there's nothing else to read while you wait for the food to arrive and have concluded that avid gardeners must be a bit dingy will have additional ammo when I tell you that the alleged mild winter being forecast is good news for everyone except gardeners. The best type of winter for Minnesota perennial flowers and vegetables (rhubarb, asparagus, etc.) is a cold one, with lots of snow. If the ground were to freeze in November and stay frozen under piles of snow through to April there would essentially be no reason to cover our beds in the fall with winter mulch, such as hay or leaves. But that rarely happens, so we must prepare.
After the ground has frozen-stick it with a pitchfork, you'll know-it is vitally important to cover garden beds with winter mulch. I usually wait until two or three good hard freezes, or a period of several days when the nighttime temperatures hit the lower 20s with daytime temperatures in the 30s. Cut perennials down to one inch and remove from beds. One notable exception is clematis, which you should leave alone. Then cover the beds in the morning, before daytime sun softens the topsoil. I am a strict proponent of marsh hay, available starting now at all the garden centers. After cutting the twine from the bale you will find the bale pulls apart in approximately eight-inch sections, called pats. I shake the hay loosely from each pat and cover all my beds with a good foot of this material. Do not use straw, for plain farmer's straw is rife with seeds, and next summer your yard will have an undeniable native prairie look to it that you hadn't intended. Marsh hay has few seeds.
I have also covered my beds with bags of leaves, and this method is quite satisfactory. If you go this route, don't fill the bags full when raking leaves this fall; make them more pillow-shaped than barrel-shaped so there is good surface contact with the frozen ground. It is important that good air circulation be maintained throughout the winter, however, which is where I think marsh hay excels. But bags of leaves are proven effective, and are certainly easier to remove in the spring than loose hay. Either way, if an early snow should fall before you've put the mulch down, fine, cover the snow with the mulch. You gained one nice, free layer of insulation.
Why are we doing all this? Winter mulch has nothing to do with keeping the soil warm. It isn't even purely to keep the soil frozen. What it does is keep the soil temperature constant. What kills perennials are freeze-and-thaw cycles, such as occur in December and January, and March and April. This is when perennials die (particularly March and April). The sun comes out hot during periods of the winter, the snow cover melts and the soil thaws. Then a week later it's cloudy and bitter cold again and the soil re-freezes; very tough on plants. With this El Nino that's being talked about, I doubt the soil will even freeze this winter (it didn't in my yard last winter). So some cool morning in late November I'll cover my beds, and if the soil winds up never freezing, fine, at least it will stay a constant temperature straight through to when I pull the hay off in April.