The key to successful winter gardening is the date of the first killing frost, which comes in late October in the Pacific Northwest. Winter crops should be in the soil early enough to reach full maturity before that date.
Accordingly, crops that need about 90 days for full maturity should be in the ground by mid-July for fall harvest. Mid-season crops that need about 60 days should be planted by mid-August. Early-maturing crops that need 30 days should be planted by mid-September.
Adding Warmth Through Constructive Gardening
Some gardeners use windbreaks and walls to add 10 to 15 degrees Fahrenheit to fall and winter gardens. Many have found that a south-facing wall of a building is ideal for construction of structures that retain solar energy for warmth.
Cloches, bell-shaped glass covers of various designs, protect plants from frost as portable greenhouses that absorb solar energy to warm what they cover. Designs range from stiff wire frames with glass panes to clear gallon-size bottles with no bottoms.
Cold frames are bottomless, boxlike structures usually covered with glass or transparent plastic. They protect against strong winds and raise day- and nighttime temperatures. An old window sash of any dimension can form a cold frame.
If the glass is broken, fiberglass or polyethylene can substitute. The ideal cold frame stands about 18 inches on one side and 12 at the opposite. The slope is for rain to run off and for an angle to catch sunlight for heat. The cold frame should face south for maximal amounts of sunlight. A slight ground slope drains water away from the frame.
Greenhouses create frost-free climates all year around. Unheated greenhouses can raise seedling crops of many of the most delicious root and leaf vegetables. Heated greenhouses can raise tropical plants. Some greenhouses as far north as Alaska produce commercial crops of tomatoes and cucumbers during the Arctic winter.
Mulch Ado about Nothing
Late October-early November is the time to prepare vegetable gardens for cold winter weather. Where the soil regularly freezes, mulch is a necessity for winter vegetables.
The temperature under the mulch will be higher than that above in the air if the mulch is in place before the ground freezes. Mulching insulates the plants with a blanket of protection over the root system to discourage winter growth of weeds and grasses.
Mulch reduces evaporation of moisture from the soil during droughts and holds soil in place to retard erosion. Good mulch traps layers of air for insulation while allowing some air to circulate.
Straw is a good choice for these reasons though it can harbor weed seeds. Leaves can make good mulch, but they compress in winter rain. For leaves, a sheet of plastic on top might be helpful.
Rotation of vegetable varieties is an important part of any garden plan. Do not plant the same fall or winter vegetable crops in the same location as in the previous year or immediately preceding summer season. The same crop in the same location not only draws down on soil nutrients but also attracts the same insects and diseases to the garden again.