You can plant vegetables earlier in the spring and harvest them later in the autumn by creating conditions that are less extreme than in the open garden. Here are some of the best methods.
Coddled in cold frames
Cold frames can lengthen the growing season by up to two months. These are bottomless boxes with clear covers set directly on the ground. You can purchase prefabricated models or build your own.
The sides may be constructed of wood, brick or cinder block. Old storm windows, clear acrylic panes or sheets of Plexiglas make durable covers; another option is UV-stabilized polyethylene or heavy-duty PolyWeave (eight-millimetre-thick polyethylene reinforced with nylon mesh). This lasts for five seasons, lets through 90 per cent of available sunlight and protects plants to –4ºC. You can also create a temporary cold frame by stacking bales of straw around plants and laying old storm windows overtop.
Site the cold frame facing south, with the back toward the north. Raise the back several centimetres higher than the front by mounding it up with soil (fill in the gaps on the sides with more soil); this angles the cover for maximum sun exposure and helps insulate the frame. Once in place, enrich the soil with your best compost to ensure good drainage and prevent roots from rotting. Put a small thermometer inside the cold frame; when the temperature reaches 22ºC, prop open the lid.
All tucked in
Placed loosely over plants, floating row covers and garden blankets made of lightweight fabric (e.g. Agronet, Agryl P17 and Reemay) let through about 85 per cent of available sunlight, are permeable to water and air, and protect plants from frost damage to –2ºC. (Peg down the edges with U-shaped metal pins or large flat-head nails.)
Floating row covers speed the growth of young plants in spring, enabling gardeners to harvest vegetables 10 to 14 days earlier than usual. Additionally, they slow the evaporation of moisture from the soil and keep pests off plants.
These covers should be replaced after 20 weeks or so of combined use.
Pampered in plastic
Plastic tunnels are essentially mini-greenhouses that can extend the growing season by three to five weeks, and are ideal for vegetables planted in straight rows.
Place a sheet of four- or six-millimetre-thick polyethylene (with a UV-inhibitor) over a series of sturdy bent wires or plastic hoops that are slightly higher than the plants. Bury the edges of the sheet in the soil and secure with bricks or stones; leave the ends open. Ventilate the tunnel and moderate temperatures by cutting vertical slits in the plastic every 30 to 40 centimetres. On nights when temperatures hover around freezing, cover the ends with squares of leftover polyethylene or newspaper.