Burnt Rhododendron Leaves: Environmental Leaf Scorch On Rhododendrons
By: Mary Ellen Ellis
Burnt rhododendron leaves (leaves that appear burned,scorched, or browned and crisp) are not necessarily diseased. This kind ofdamage is most likely due to unfavorable environmental and weather conditions.There are some things you can do to prevent curled, crispy rhododendron leavesand repair damaged plants.
Signs and Causes of Rhododendron Stress Burn
Stress burn or scorch is a phenomenon that is not uncommonin broadleaf evergreens like rhododendron.The stresses triggered by unfavorable weather can cause:
- Browning on the tips of leaves
- Browning along the margins of leaves
- Extended browning and crispy leaves
- Curled leaves
Scorch can be caused by dryness in winter.Especially windy and cold conditions can cause the leaves to lose more waterthan the roots can take up in frozen soil. The same thing can happen duringparticularly hot, dry conditions including summer droughts.
It’s also possible that stress burns and scorch aretriggered by excessive water. Standing water and boggy conditions can causeenough stress to damage leaves.
What to Do with Rhododendron with Scorched Leaves
Damaged leaves and branches may or may not recover. Leavesthat curled up over the winter are protecting themselves and will likely openup again in the spring. Leaves with excessive browning from winter or summerstress probably will not recover.
Watch for recovery and if leaves don’t bounce back orbranches don’t develop new buds and growth in the spring, trim them off theplant. You should get new growth in other areas of the plant in the spring. Thedamage is not likely to destroy the entire rhododendron.
Preventing Leaf Scorch on Rhododendrons
To prevent winterrhododendron stress burn, take good care of the bushes during the growingseason. This means providing at least an inch (2.5 cm.) of water per week. Wateryour rhododendrons each week if rain is inadequate.
Take care in providing enough water in the fall to ready thebush for winter conditions. Watering in the summer when temperatures are highand drought is possible is also important for preventing summerstress burns.
You can also choose a more protected location for plantingrhododendron to prevent winter and summer injury. Adequate shade will protectplants in summer and wind blocks will help them avoid damage in both winter andsummer. You can use burlap to block drying winter winds.
Prevent stress caused by standing water as well. Only plantrhododendron shrubs in areas where the soil will drain well. Avoid boggy,marshy areas.
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Read more about Rhododendrons
How to Revive a Burned Azalea Bush
Azaleas (Rhododendron spp.) are small shrubs that produce big, bright flowers in the early spring and are cold hardy in U.S. Department of Agriculture zones 4 to 9 depending on the species. While some azaleas are well-suited to certain areas of the United States, azalea dieback is common for some species in Northern zones. Azaleas look bad after they suffer from winter burn, but this is preventable with the proper care.
Rhododendrons Curl Their Leaves Against Winter Wind
If a lot of cold wind blows past your rhododendron in the winter, it will curl its leaves inward so less leaf surface is exposed the plant’s trying to keep water from evaporating out of its leaves. Here’s how to help: Whenever the temperature gets above freezing, give your rhododendron a slow and steady trickle of water until the soil feels damp 8-10 inches down.
Keep that needed moisture in the ground by adding two inches of mulch. The mulch layer should cover an area starting two inches away from the trunk and going out beyond the ends of the branches. Next fall, get your rhododendron ready for winter by makes sure it gets at least an inch of water (from rain or from you) each week.
The October Garden
The glory of the sino nuttallii rhododendrons
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Rhododendons may no longer be the elite fashion item they were for so many decades, but we still love them.
When we started in the plant business back in the early 80s, rhododendrons were a hot ticket item. We were but one of several rhododendron nurseries in Taranaki and to survive, we needed to find our own niche. To this end, we grew a different range, specialising in varieties that would perform well in warmer climates – like Auckland. After all, even back then, one in four New Zealanders lived in greater Auckland and we figured that if we were going to sell them rhododendrons, we might as well sell them ones that would do better for them. Mark’s father just happened to have done some breeding to find varieties that were more resistant to thrips, didn’t get that burned and crispy edging to their foliage and were predominantly fragrant as well as floriferous. It gave us a good place to start.
Nowadays there are no specialist rhododendron growers in Taranaki at all and the demand has melted away. I no longer have to try and convince people that not all rhododendrons have a big full truss in the shape of a ball but many have loose trumpets in curtains of bloom instead.
Rhododendrons are one of the backbones of our garden and we wouldn’t have it any other way. While they have a relatively short season in full bloom, the anticipation of fattening buds stretches out the weeks with the promise of delights to come. They are as fine a shrub as any we grow here and a great deal more spectacular than most.
The nuttalliis! Oh the nuttalliis!
The nuttalliis. Oh the nuttalliis. Peak nuttallii season doesn’t start until closer to the end of the month, taking us into November but some varieties have already done their dash for this year. If we could grow only one type of rhododendron, we’d choose a nuttallii and even more specifically, the sino nuttallii from China. You can keep your big red rhodos (most people’s favourite pick). We love the fragrant, long, white trumpets which look as if they are made from waxed fabric, the lovely peeling bark and the heavy textured foliage. These are rarely offered commercially now so grab one if you ever find it for sale.
It is, by the way, nasty little leaf-sucking thrips that turn foliage silver and no, you can never turn those silver leaves green again. If you look at the underside of the leaf, you can see dark thread-like marks – these are the critters that do the damage. All you can do is to try and prevent the new season’s growth from getting similarly infested. We are not at all keen on spraying insecticide these days and you need a systemic insecticide that the plant absorbs into its system to get a thorough kill. If you must go down this path, spray in mid November, early January and late February for maximum effect. Others praise Neem oil instead but we haven’t tried it.
We favour choosing more thrip-resistant varieties, keeping them growing strongly and opening up around them to let more air and light in. Thrips prefer shade and shelter. Unless it is really
special, if it is badly thrip-prone, we replace it with a better variety. Not every plant is precious.
In the longer term, plants come and go in the fashion stakes. Goodness, even red hot pokers are having a resurgence of popularity. We don’t worry about the fashion status of the rhododendron and Mark continues hybridising for better performing cultivars. If there is no commercial market for the results, it doesn’t matter. We will continue to enjoy them in our own garden.
First published in the New Zealand Gardener and reprinted here with their permission.
Rhododendron Barbara Jury – one of Felix’s hybrids
Summer drought combined with high temperatures and brief sun can scorch leaves.
Note how the necrotic areas are all at the tips of the leaves.
Photo by Jay W. Pscheidt, 1994.
Cause Leaf scorch on rhododendrons is a response to stress. Water stress can occur under both extremes of flooded, overly-saturated soils or under drought conditions when too little water is present. Root or stem damage due to disease or transplant shock can also cause scorch symptoms. High soil pH and exposure to drying winds are other possible causes of leaf scorch. Too much salt in soil or irrigation water, or using large amounts of inorganic fertilizers, or a combination of all three can cause symptoms as well. Plants in containers or not receiving enough water are often salt damaged, which also predisposes them to other problems such as Phytophthora root rot.
Symptoms Symptoms include browning of tips or margins of leaves, with the damage sometimes spreading to the center of the leaf. The south/southwest side of the plant is the most likely to be damaged by direct sunlight, but plantings also might be damaged by reflected sunlight.
Leaves that are yellow between the leaf veins are showing symptoms of a pH problem, or an iron, calcium or magnesium deficiency. These problems may be interconnected, as a pH imbalance may prevent uptake of certain nutrients. An overall yellowing of the whole plant may be a nitrogen deficiency. Young leaves that are reduced in size, slightly cupped and have burnt tips are often suffering from copper deficiency. If leaves are very dark green and reddish on the lower side, phosphorus deficiency may be the problem.
- Leaves that are yellow between the leaf veins are showing symptoms of a pH problem, or an iron, calcium or magnesium deficiency.