EUGENE, Ore. – Perennial vegetables can survive winter's freezing temperatures with a little extra care before winter cold sets in.
If you mulch your rhubarb, asparagus, horseradish and artichokes to insulate against the cold, you're also enriching the soil for next spring, according to Pat Patterson, Master Gardener volunteer with the Oregon State University Extension Service in Lane County.
"Organic matter and well-rotted manure assure a good crop next year," Patterson said.
If your rhubarb is crowded and well-established, fall is a good time to renovate the plant, a task that needs to be done only every few years. Drive the blade of a shovel down through the middle of the plant. Then remove half of the plant—crown, roots and all. Fill the hole with compost, rotted manure, or fertilizer mixed with organic matter. Compost the removed half, move it to another spot or give it to a friend who needs rhubarb. Dividing may also be done in early spring.
Mulch asparagus beds with four to six inches of chopped leaves, weed-free straw, hay or similar materials. Next spring, remove the mulch from half of the bed. The asparagus will come up more quickly where the mulch is removed and the mulched section will come up later, thus extending your asparagus season. Take the mulch off soon after spears begin emerging or they will curl over.
"Horseradish will winter-over with no mulching in most places west of the Cascades," Patterson said, "and just a light mulching is needed in the colder parts of the state. Horseradish is best and most potent when it’s harvested after several good frosts in the fall."
Treat Jerusalem artichokes in the same way as horseradish. Do not harvest until the tops have died.
To ensure the survival of thistle-type artichokes (Globe, for example), clip back the large artichoke rosette. Cover it with six inches or more of mulch, compost or leaves. If there are baby plants, “pups” coming up around the mother plant, remove the mother plant entirely and protect the pups.
During the harshest part of winter, put a heavy cardboard box with the bottom open over artichoke plants. A Styrofoam box also works very well. Then fill the box with straw, mounding it over the cut-back plant or pups. Remove the box when the weather moderates. Take away the mulch after most danger of frost has passed in the spring. In a mild winter, artichokes will survive without protection west of the Cascades.