rhododendron - Ask Extension
My rhododendrons look miserable. We put them in about two years ago. The first year they had a few blooms, none last year or this year. What can I ...
Knowledgebase
rhododendron #867938
Asked May 10, 2024, 6:11 PM EDT
My rhododendrons look miserable. We put them in about two years ago. The first year they had a few blooms, none last year or this year. What can I do to get them into shape and get them to perk up and bloom? Thank you.
Caledonia County Vermont
Expert Response
Alice
Thanks so much for reaching out to the UVM Extension Master Gardener Volunteers! And thank you for sending the photos. Always helpful.
I can see that your shrubs appear small, and one looks like it has some winter injury. Since I don’t know your site exposure or your elevation, I will provide you with general care information for your Rhododendrons in hopes it will help get you - and them on the right path.
Most important thing is having the right plant for the place.
Hardiness is the first thing to consider. Rhododendrons should be hardy enough to survive in the zone they are planted without too much extra care. In most of Vermont, this means selecting plants which are hardy in zones 3-5. I could not see the detail on the plant tag to tell what variety or hardiness zone your rhododendron is, but I’m hopeful you picked ones that are right for your planting zone.
Rhododendrons appreciate a spot with dappled shade or at least protection from hot afternoon sun and strong winds. Too much sun leads to bleached and burned leaves while heavy shade causes lanky growth and poor blossoming. One rule of thumb is the larger the leaf the more shade they prefer. And they love to be well watered when settling into their new location.
For optimum growth, most rhododendrons require one inch of rainfall or supplemental irrigation every week. Fall watering is extremely important and should continue until the temperature drops below 40 degrees. Also avoid fertilizing after mid-September because it may delay dormancy.
Since harsh winter winds and sun can damage rhododendrons, they should be planted in partially shady areas where they are protected from prevailing winds. Avoid planting in dry soil, full sun, or on exposed windy sites. Avoid exposed southern or western sites where winter sun and wind will cause the most damage.
If they need to be moved to a better site location, now would be the time.
Winter prep/injury
When the ground is frozen, the rhododendron roots can’t take up enough water in the soil to make-up for what is lost through the leaves. The leaves curl and droop and may turn brown at the tips and edges. Curling their leaves is a protective mechanism against dehydration during cold periods, and normally the leaves unfurl when it warms up. Often, damage that occurred over the winter does not become apparent until the spring.
Snow acts as an insulator, protecting leaves that are underneath the snow, and helps moderate the soil temperature. The state of different rhododendrons may also have to do with variety. Many hybrid rhododendrons, which are very popular as landscape plants, are not as cold hardy as species types.
If you believe that your rhododendrons suffered from winter injury, the best thing you can do now is wait to see if any of the damaged branches survived. It’s possible to sustain leaf damage without the branch and buds being killed.
Branches that don’t show any signs of life once growth resumes in the coming weeks and months should be pruned out. Buds are generally hardier than leaves and are much better at surviving extreme weather conditions. By the end of June, rhododendrons should have produced new leaves, at which point dead branches should be removed.
Other important measures include mulching or using physical barriers such as burlap to block the wind. Mulching rhododendrons, especially those that have been newly planted, insulates the soil and protects the plant’s roots. At least two inches of woodchips or straw should be applied over the root zone, taking care not to pile the mulch against the trunk. Creating windbreaks from materials such as burlap or canvas may also help.
Resources:
It seems a bit early for your rhododendrons to be in bloom, so give it some time. For this year, I would focus on establishing a hardy shrub and hope that next spring they will bloom for you.
In summary -
1. Provide some shade and wind protection
2. Water 1 inch a week until temperatures drop below 40 degrees.
3. Provide winter wind protection in the late fall
4. Transplant now if the shrubs aren't in the optimum spot
I do hope this information has been helpful.
Thanks so much for reaching out to the UVM Extension Master Gardener Volunteers! And thank you for sending the photos. Always helpful.
I can see that your shrubs appear small, and one looks like it has some winter injury. Since I don’t know your site exposure or your elevation, I will provide you with general care information for your Rhododendrons in hopes it will help get you - and them on the right path.
Most important thing is having the right plant for the place.
Hardiness is the first thing to consider. Rhododendrons should be hardy enough to survive in the zone they are planted without too much extra care. In most of Vermont, this means selecting plants which are hardy in zones 3-5. I could not see the detail on the plant tag to tell what variety or hardiness zone your rhododendron is, but I’m hopeful you picked ones that are right for your planting zone.
Rhododendrons appreciate a spot with dappled shade or at least protection from hot afternoon sun and strong winds. Too much sun leads to bleached and burned leaves while heavy shade causes lanky growth and poor blossoming. One rule of thumb is the larger the leaf the more shade they prefer. And they love to be well watered when settling into their new location.
For optimum growth, most rhododendrons require one inch of rainfall or supplemental irrigation every week. Fall watering is extremely important and should continue until the temperature drops below 40 degrees. Also avoid fertilizing after mid-September because it may delay dormancy.
Since harsh winter winds and sun can damage rhododendrons, they should be planted in partially shady areas where they are protected from prevailing winds. Avoid planting in dry soil, full sun, or on exposed windy sites. Avoid exposed southern or western sites where winter sun and wind will cause the most damage.
If they need to be moved to a better site location, now would be the time.
Winter prep/injury
When the ground is frozen, the rhododendron roots can’t take up enough water in the soil to make-up for what is lost through the leaves. The leaves curl and droop and may turn brown at the tips and edges. Curling their leaves is a protective mechanism against dehydration during cold periods, and normally the leaves unfurl when it warms up. Often, damage that occurred over the winter does not become apparent until the spring.
Snow acts as an insulator, protecting leaves that are underneath the snow, and helps moderate the soil temperature. The state of different rhododendrons may also have to do with variety. Many hybrid rhododendrons, which are very popular as landscape plants, are not as cold hardy as species types.
If you believe that your rhododendrons suffered from winter injury, the best thing you can do now is wait to see if any of the damaged branches survived. It’s possible to sustain leaf damage without the branch and buds being killed.
Branches that don’t show any signs of life once growth resumes in the coming weeks and months should be pruned out. Buds are generally hardier than leaves and are much better at surviving extreme weather conditions. By the end of June, rhododendrons should have produced new leaves, at which point dead branches should be removed.
Other important measures include mulching or using physical barriers such as burlap to block the wind. Mulching rhododendrons, especially those that have been newly planted, insulates the soil and protects the plant’s roots. At least two inches of woodchips or straw should be applied over the root zone, taking care not to pile the mulch against the trunk. Creating windbreaks from materials such as burlap or canvas may also help.
Resources:
Rhododendrons and Other Broadleaved Evergreens Showing Signs of Winter Damage | Extension (unh.edu)
Rhododendrons and Other Broadleaved Evergreens Showing Signs of Winter Damage | Extension (unh.edu)
It seems a bit early for your rhododendrons to be in bloom, so give it some time. For this year, I would focus on establishing a hardy shrub and hope that next spring they will bloom for you.
In summary -
1. Provide some shade and wind protection
2. Water 1 inch a week until temperatures drop below 40 degrees.
3. Provide winter wind protection in the late fall
4. Transplant now if the shrubs aren't in the optimum spot
I do hope this information has been helpful.
