It should go without saying that water is vital for plant survival. Plants use water for photosynthesis, transporting water-soluble nutrients, and maintaining turgidity. Turgidity is the water pressure against the inside of a plant’s cell walls that keep plants upright and supple. When a plant lacks water, decreased turgor pressure causes the plant to wilt. During the spring, summer, and fall, wilted leaves indicate a plant lacks water, and experienced gardeners know supplemental water is necessary to ‘perk it up.’ But during the winter, when many plants lose their leaves or wilting leaves are harder to recognize, how do gardeners know when to water?
First, it is helpful to know that South Carolina receives 45 to 50 inches of rainfall annually, well above the Earth’s average of 39 inches per year. Summer heat causes water to evaporate more quickly, causing plant drought stress during periods of hot, dry weather. With adequate rainfall, established plant species appropriate for our climate typically need little to no supplemental irrigation during the winter.
Exceptions to this rule include newly planted trees and shrubs, plants in containers, and periods of unusually dry winter weather. We plant trees and shrubs to take advantage of cooler temperatures in the fall, allowing plant roots to grow while aboveground growth is dormant. The developing root systems of newly planted shrubs cannot access the same soil volume for moisture as established plants. Therefore, it is necessary to monitor moisture around their root balls carefully. During periods with no rain, check soil moisture weekly and water when the soil seems dry.
Plants in containers have limited soil volume from which to access water. Additionally, potting mixtures are porous and made to drain water quickly. Therefore, it is crucial to monitor the moisture in containers throughout the winter to keep them from drying out.
The rules for winter irrigation for lawns are more complicated. Visit HGIC 1803, Landscape Irrigation Management Part 4: Winter Irrigation & Winterizing & Winter Irrigation for Turfgrass Lawns for more information about winter lawn irrigation.
Two essential but often overlooked tools in your irrigation toolbox are your fingers and eyes. Pull back the mulch, stick your finger in the soil, feel and look to see whether the soil is moist. If it is moist, there is no need to water. If it is dry, apply water when temperatures are above freezing.
Finally, do not forget to mulch! Mulch helps retain soil moisture, moderates soil temperatures, and adds organic matter to the soil over time. For more information about mulching, visit HGIC 1604, Mulch.