Oblong, 4- to 8-inch, leathery, dark green leaves are rusty orange underneath.
Rhododendron maximum is toxic to people and animals.
Rhododendron Maxiumum Care
Finding the right outdoor conditions for this acid-loving plant is essential.
Arx Fortis / Wikimedia Commons / CC BY-SA 3.0
It’s rabbit resistant with an open form that suits natural areas including woodland margins and shrub borders.
Light
Choose a location in dappled shade.
This rhododendron will grow in nearly complete shade but flowering may be sparse.
Direct sunlight, especially hot afternoon sun will burn foliage.
Shrubs should receive no more than two hours of direct morning sunlight daily.
Consider planting in raised beds instead of heavy clay soils.
Add compost or other organic materials to enrich and aerate soil for adequate drainage.
Water
Water new plants twice weekly in the first year.
Once established, water only during dry periods lasting two to three weeks.
Mulch with wood chips, pine needles, or straw to improve moisture retention.
Heat is the greater concern with ideal temperatures between 45F and 60F.
Humidity levels between 40 and 60 percent provide optimum health.
Fertilizer
Little to no fertilization is needed except in poor soil.
Rhododendron maximum needs nitrogen for healthy foliage and phosphorous for flowering.
Apply organic nitrogen fertilizer in spring according to product directions.
In cold climates withhold fertilizer after June.
Types of Rhododendron Maximum
Rhododendron maximum is a single species in the genus.
Here are some other cold-hardy, evergreenrhododendronswith exceptional foliage and flowers.
Pruning
Many types of rhododendrons look best left to grow naturally withlittle to no pruning.
Remove dead and damaged branches and save heavy pruning for late winter when shrubs are dormant.
Rejuvenate an overgrown shrub over several seasons by cutting back selected branches up to one-third.
Remove branches that cross or touch the ground to improve air circulation and discourage pests.
Propagating Rhododendron Maximum
Propagation is done with stem cuttings or by layering.
Stem cuttings are taken in autumn and root fairly quickly.
Softwood cuttings root more easily than hardwood stems, however they are more vulnerable to fungal infections.
Treat with rooting hormone that includes a fungicide.
The germination rate is excellent and sprouts appear in three to eight weeks.
A thick layer of mulch is adequate to safeguard the shallow root system.
Common Pests and Plant Diseases
Rhododendrons are vulnerable to a number of insect pests and diseases.
Choosing the right environment and maintaining healthy shrubs helps limit some of the following problems.
In cases of infestation, apply an appropriate pesticide following label directions.
Plant so roots lay just below the soil surface.
Develop good pruning practices and deadhead spent flowers.
Apply fungicide when needed for leaf spots, rust and powdery mildew.
How to Get Rhododendron Maximum to Bloom
Rhododendron blooms profusely with the right growing conditions.
Add organically rich compost to the soil and support flowering with an acid-based fertilizer in spring.
Bloom Months
Buds appear in late spring opening to abundant flowers in June and July.
How Long Does Rhododendron Maximum Bloom?
Length of bloom period is dependent on weather conditions but flowers often last about three weeks.
What do Rhododendron Maximum Flowers Look and Smell Like?
Flowers are lightly fragrant attracting pollinators including bees, butterflies, and hummingbirds.
Apply fertilizer formulated for rhododendrons and acid-loving plants in early spring.
Dead and damaged branches should be removed but avoid heavy pruning during the growing season.
It promotes new growth that won’t reach maturity before dormancy and will be vulnerable to winter damage.
Keep shrubs free from weeds but avoid mechanical cultivation which can damage shallow roots.
Water during periods of drought lasting two weeks or longer.
Deadheading Rhododendron Maximum Flowers
Deadhead faded and spent flowers by clipping them at the stem base.
Nitrogen also plays an important role in acidifying soil.
Prevention is the best cure.
Transplant new shrubs with the crown slightly above soil level to improve drainage.
Leaf and Flower Galls
Galls cause distortions in leaves, flowers and stems.
Protect plants in autumn and early spring with an utility of dormant oil.
Treat just before dormancy in autumn and just after bud break in spring.
Rhododendron maximum grow from 5- to 15-feet tall and 5- to 12-feet wide.
Rhododendron catawbiense is found more often, but not exclusively, at higher elevations.
Flowers are purple to lilac while R. maximum flowers have a reddish tinge.
The undersides of R. maximum leaves are coppery orange and R. catawbiense leaves more yellow-green underneath.
It also can grow larger than R. maximum, up to 20 feet tall.
