Ground moisture becomes an issue for evergreen trees and shrubs and some perennials when the temperatures warm and very little snow falls. As everyone has noticed our weather is very mild this winter. It certainly contrasts with last winter’s snow and cold.
Evergreen trees and shrubs continue to trans-evaporate and suffer with lack of soil moisture. Trees have surface roots that extend far beyond the extent of the canopy. Those extensive roots in landscape trees are typically watered during the summer by lawn and garden irrigation. In the winter, they don’t get that extra water.
Evergreens need a good soaking once in a while to saturate the ground during mild winters particularly trees planted less than 2 years ago. On warm days with no moisture in the forecast, I use a soaker hose and lay out the coils around the tree and let it soak for a couple hours. I also frequently fill the basin around young evergreens I recently planted. It has been so mild, I have not stored my garden hose in the garage but keep it drained and ready to connect to the faucet outside.
Fall planted perennials are the most at risk of suffering from mild winters because they haven’t had time to grow a deep root system. A good thick layer of mulch such as leaves in the fall help perennials get through mild winters. Care should be taken however to not smother certain low water plants that don’t do well with moisture on their stems in winter such as hummingbird mints (Agastache), certain sages (Artemisia and Salvia), and penstemons. In these cases use a rock mulch around the base without covering the stems. They will be much happier.