Creating Microclimates to Protect Plants
Four Season Garden: Gardening for Climate Change
Microclimates in the garden can protect plants from fluctuating weather.
Climate change is bringing a new challenge of weather extremes to gardeners and farmers across North America. The predictable weather patterns we knew and counted on are becoming more unpredictable. One week the weather is hot and sunny—perfect for tomato transplants. The next week a cold wind pushes over young plants and chills their roots. It’s confusing to the plants, and to the growers too.
Adapting your growing area to protect young plants from heat, drought, wind, rain, and cold is a key to growing successfully. You can do this by creating microclimates that offer protection to vulnerable plants.
Microclimates are small areas that have different growing conditions from the surrounding region. Sun traps, wind buffers, and radiant heat producers create microclimates that shelter plants from cold. In drought conditions, a cool microclimate affords shade and water retention to minimize heat stress.
How to Use Microclimates to Protect Plants from Changing Weather
Protecting Plants from Heat and Sun
Too much heat and sun exposure dries out vegetation. Excessive heat causes leaf wilt as plants transpire moisture to protect themselves from high temperatures and sun. During warm spells, cool season vegetables like lettuce and spinach are quickly stressed and will shoot into flower. At temperatures over 30º C (about 90º F), tomatoes and peppers will often become sunburned and stop flowering.
• Provide shade for garden plants when it is hot. To alleviate heat, cast a shadow over plants with an umbrella, shade cloth, or any light fabric stretched out along a support. Tall flowers or trellises can also provide shade for seedlings and vulnerable transplants.• Mulch around vegetable plantings with straw, leaves or dried grass clippings to cool and keep the soil moist. In very hot conditions, use a thick mulch 10–15 cm (4–6 inches) deep to provide protection.
• Consistent watering creates a stable environment for plant growth. During hot periods, water in the morning or early evening so moisture can reach the plant roots without evaporating. Deep watering 2-3 times per week keeps the soil more evenly moist than superficial watering.
Wind dries out seedlings and young plants. It chills the roots and stems, and can blow over growing vegetables.
• Buildings, fences, trees and shrubs can alter wind patterns, creating protected zones. Tall vegetables or vine-covered trellises offer shelter from the wind to nearby plants. Conversely, these barriers create a cold zone on the side facing the wind.
• Pails, straw bales, glass window panes, or garden furniture set up strategically to obstruct wind will warm roots and protect tender stems of new transplants.
Protecting Plants from the Rain
Heavy rains and standing water leave plants overly wet. Too much rain washes away seeds, damages seedlings, chills plants and compacts the soil.
• Large trees offer rain protection to plants growing under their canopies. Trees roots, however, sometimes compete for available nutrients and water, making it hard to grow smaller plants near the base.
• Building overhangs create a rain shadow, preventing precipitation from reaching the ground and keeping plants dry. Hand built supports covered with heavy plastic or glass panes can provide rain protection while still allowing ample light.
• Portable buffers for rain, cold and wind include cloches, upside down plastic milk jugs, jars or pots over seedlings. Plastic- or burlap-wrapped tomato cages will also shelter transplants.
Protecting Plants from the Cold
Cold has a lot to do with location. A northern exposure lacks sun and will be colder and often shadier than other orientations. The top of a hill is coldest and windiest. Cold air and water flow down and can pool at the bottom. Midway down a slope is more moderate.
• Raised beds or terraces, oriented to the south, can mitigate cold by warming and draining the soil quickly. Raised beds warm up earlier in the spring than the surrounding lower ground.
• Sun traps take advantage of sun exposure and radiant heat. Sun exposure is warmest when facing south. A western exposure is also warm. Planting against a south or west wall or fence creates a sun trap that captures warmth for heat-loving plants like tomatoes and peppers.
• Dark-coloured mulch such as black plastic will heat the soil and encourage early plant growth.
• In cool seasons, greenhouses, hoop houses, row covers and cold frames can extend the growing season and protect plants from cold, frost, wind and rain.