Shown above are rhododendron leaves curling up tight for protection against frigid weather this past winter when the temperature was -15 degrees F. Shown below is the same rhododendron on an April day when temperatures were in the mid-50s. The leaves are unfurled and some exhibit winter damage with browning leaf edges.
Photos: Dayle Davis
A: This question is timely after such a rough winter. Your plant is exhibiting the effects of winter burn. Rhododendrons have a defense mechanism against frigid temperatures. The sides of the leaves roll toward each other, which causes a drooping, cylindrical appearance. The colder it gets, the tighter the leaves roll and droop. I liken this practice to my childhood when the school bus was late picking us up in winter. My sister and I would hunker down to our ankles and huddle together for warmth. Eventually, we’d arrive at school and thaw out. No such luck for rhododendrons. They are stuck where they are planted.
It is always best to plant rhododendrons (and azaleas, which are closely related) in small groups in a site that is somewhat sheltered from wind and receives only dappled sunlight in summer. Also, it is imperative that the plant is situated in an area that receives no morning sunlight in winter. That’s because in winter, the early morning sun will warm the plant, which allows water to transpire from the leaves and buds but with no way to receive a fresh supply of water from the roots which are still frozen in the soil. The result is desiccation, or dryness, which causes the leaves to brown and the flower buds to die.
Rhododendrons are under-story plants. In their natural habitat, rhododendrons grow on shady forest floors covered with a surface layer of decaying leaf litter. Therefore, they will fare best in your garden when planted near a structure or in a site protected by windbreaks such as fences or evergreens. The best sites for planting are on the north side of a building, then the east side and finally, the west side. Avoid the south side of a building unless it is protected from winter sun. (Note: Do not plant rhododendrons under the eaves of a building where little or no rainfall wets the soil.)
Probably the most important requirement for healthy rhododendrons is soil preparation. Always perform a soil test first and amend the planting site according to the test results. Do this in the fall and allow the soil to mellow over winter before planting in spring. The soil for these plants must be moist, well-drained, well-aerated and have a pH of 4.5 to 5.5. Fifty percent of the planting mix should be organic material. Combine organic material such as sphagnum peat moss, pine bark mulch, compost and aged, chopped leaves and work it into the soil to a depth of about a foot. Pine bark is a particularly good ingredient of the planting mix. The added material will raise the bed and allow good drainage and aeration of the soil.
While curling leaves in winter mean the plant is seeking protection from cold, curling leaves on a rhododendron plant in summer means water deficiency. It is at this stage that the plant must be watered immediately to ward off the next stage — actual wilting. Wilting greatly stresses the plant and can lead to stem dieback.
It is also imperative that rhododendrons have enough water before the soil freezes in the winter to minimize water loss through the leaves that cannot be replaced when the soil is frozen. If autumn rainfall is scarce, water the plants well by late November.
Fertilize rhododendrons annually in late autumn after a hard freeze or early spring using a fertilizer specifically formulated for acid-loving plants. Do not fertilize after June 1.
Deadhead the large leaf rhododendrons to remove spent flower trusses after they have finished blooming. This will direct energy to produce more flower buds for next year.
As to the damaged browning leaves, if only brown at the edges, I usually leave them in place. If mostly brown and unsightly, they can be gently snapped away from the branch and removed. Dead brown leaves will drop away on their own.
For those plants already situated in an undesirable spot, they can be transplanted to a better place or protected with wind shields placed around the plants during the winter months. Mulching is critical to help prevent winter injury.
Q: I want to grow some spring vegetables and don’t know where to start. When should I plant lettuce, cucumbers, carrots and tomatoes?
A: Lettuce and carrots can be planted now. Traditionally, cucumbers and tomatoes are planted on Memorial Day weekend or after all chance of frost is past.
For more horticultural information, call The Ohio State University Summit County Extension Hotline Tuesdays from 9 a.m. to noon at 330-928-4769, ext. 3, and request Fact Sheet HYG–1078–01, “Growing Rhododendrons and Azaleas in Ohio” and HYG-3043-96, “Maintaining Healthy Rhododendrons and Azaleas in the Landscape.”
Please note fact sheets are sent out free; there is a fee for bulletins. Many bulletins are available online at ohioline.osu.edu and can be printed from home or accessed at a public library.
Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and course work in botany, geology and wildflowers. Davis is a master gardener emeritus under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition, as well as about the OSU Master Gardener program. Questions can be emailed to firstname.lastname@example.org, faxed to 330-665-9590 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material. Inquiries about area garden clubs or groups should be sent directly to the particular organization in question.
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