Why Did My Ever-greens turn into Ever-browns?
Last winter was one of the longest and coldest in recorded history. We finally started seeing the warmer end of the long cold tunnel when many of us couldn’t believe our eyes what we saw happening to our evergreen trees in our yards; many trees such as spruce, Scots pines, mugo pines, cedars and junipers started to turn brown. Some showed the browning on one side or the tops while others were browning on the whole plant.
Here are some explanations of these sad and often plant-destroying phenomena.
Some selections of Scots pine yellow naturally during the fall, but with the return of spring, they turn green again. Several juniper species turn purple or purple-brown as the temperatures drop in the fall.
Winter injury includes winter desiccation (drying), sunscald and cold-temperature damage. Springtime needle discoloration on previously healthy evergreens is often a symptom of some form of winter injury.
Winter damage has several symptoms, depending on the species and the severity of the damage. The leaf scales of cedars fade from green to light tan or reddish-brown. Needle tips of spruce and pine turn brown and become dry. The damage may occur on a few branches, at the treetop only, on one side only, or on the entire tree. Severe winter injury may cause the loss of most of the needles and the death of the plant.
Winter hardiness is influenced by a number of factors:
– Plant variety and hardiness
– Soil drainage which affects the health of the plant
– Geographic location
– On-site location (exposure)
– Environmental conditions of the previous summer and fall:
A warm fall followed by an abnormally fast drop in temperatures in October or November may result in improperly hardened plants, which were unable to convert their cell liquids into ‘antifreeze gel’. Late-season nitrogen fertilizer application will delay fall maturity and will increase susceptibility to winter injury.
Winter drying of needles will occur in abnormally warm winters because moisture is continuously lost and cannot be replaced, as the plants are dormant. On warm, sunny winter days, radiation from the sun or reflection from snow and light-coloured buildings can increase leaf temperatures to 20C° over air temperatures. The moisture in the stems and branches becomes exhausted because of the increased loss triggered by the warmer temperatures.
Dry soils are more likely to predispose roots to damage than soils that contain a good moisture supply. Root injury may be worse during winters with little snowfall. Winter root damage may not be noticed until the following summer when the plants suddenly turn brown and die.
Reducing winter injury
Using a few precautions can minimize winter injury to evergreens:
- Use hardy plant varieties recommended for our horticultural hardiness zones (2, 3A and 3B)
- Try to avoid planting evergreen trees and shrubs near light-coloured or reflective structures.
- Damage is usually reduced in sites protected from the wind. Wind draws out moisture from the scales and needles.
- Do not apply nitrogen fertilizers after July.
- Water evergreens heavily in the fall, after deciduous trees have lost their leaves, to ensure that the plants have sufficient moisture in the root zone to prevent freeze-drying. Use a root feeder or let a small trickle of water flow under the drip line of the plant for several hours. Repeat this watering early in the spring, once the ground thaws. The importance of adequate fall watering cannot be overemphasized, since this moisture uptake will enable the plant to draw from it during the months of frozen ground.
- Erect burlap screens on the south and west sides of exposed small evergreens to prevent desiccation (drying). This protection will shade the plants and prevent excessive moisture loss by the wind. Screens should be about one foot away from the plant material.
- Wrapping evergreens with burlap or plastic is not recommended because on warm sunny days throughout the winter, the internal temperature will get too high. This high temperature may cause warmed tissue to be damaged by the severe cold that follows. Plants wrapped this way may also break dormancy too early in the spring.
What to do with the brown evergreens?
The best thing is to wait and let the plant fight for itself. If the plant is still viable it will show signs of new growth now. On the spruce and pines the buds will have stretched into light green shoots, the ‘candles’. They will grow into new branches with needles. The brown dried needles will fall off. The cedars will show some small new growth further in on the branches where dormant buds are activated to take over for the lost scales.
Once the new growth shows what parts of the plant are still alive, the decision can be made to keep and lightly prune it or to remove it if the damage is to great.