Rhododendrons planted in the full sun or on the south side of a home often suffer the most severe leaf scorch. The drying effects of the sun cause the rhododendron to lose water. Rhododendrons planted in an open area can also experience scorch from the drying effects of the winter wind. The margins of the leaves are the first region to lose moisture. The leaf develops a brown, crispy fringe.
A broadleaf evergreen, the rhododendron's foliage often sustains winter injury. The affected leaves appear burnt and crispy around the margins and there may be surface yellowing. If the leaves are extensively damaged, they fall from the rhododendron during the late summer. The twigs of the rhododendron also may also die back. Because winter damage is not a disease, the rhododendron usually recovers without treatment. Preventing the leaves from becoming damaged during the cold, long winter helps the plant remain green all year long.
Winter Wind and Sun
Root System Injury
A newly transplanted rhododendron is more susceptible to the drying effects of winter. Its root system is often unable to develop prior to the cold weather and may have been damaged during the transplant. The slightest bit of damage to the rhododendron's roots affects its ability to absorb water, especially during the dry winter. An established rhododendron's root system also can be damaged from excessive cultivation. Applying too much phosphate or lime may have the same effect.
Rodents and Ice
In the summer, moles often burrow beneath the rhododendron shrub in search of grubs. After the moles move on, mice inhabit the tunnels during the winter and may chew on the rhododendron's roots. The rhododendron is weakened from injury to its root system. The damaged roots cannot adequately absorb water during the winter and the plant's leaves begin to show damage. Excessive ice buildup on the rhododendron's foliage during the winter also causes brown and yellow spots, even if the root system shows no damage. The sun shines through the ice crystals and burns the shrub's foliage.
Plant the rhododendron in a sheltered location where it will not receive the full force of the winter wind. Consider planting it in a shady spot on the north side of the house to protect it from the drying effects of the sun. Watch for moles during the summer and promptly fill in any holes the pests cause. Avoid overcultivation around the rhododendron's roots. Take care with the shrub's roots when transplanting. Applying mulch around the rhododendron helps keep the soil moist during the winter. Water the rhododendron in the winter months if the soil is not frozen.
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