Caption
Rhododendrons are popular among gardeners with their evergreen shrubbery and early blooms.
Planting
Most large-leafed varieties require dappled shade; avoid deep shade or full sun. A sunny spot that receives a few hours of shade is perfect. See regional guidelines below.
Soil should be well-drained, humus-rich, moist, and acidic (pH 4.5–6).
Azaleas and rhododendrons have shallow root systems and need moist soil and mulch to keep them from drying out. Amend planting areas with compost, peat moss, or a substitute, only if your soil is poor. Learn more about soil amendments and preparing soil for planting.
→ Not sure which hardiness zone you’re in? See the USDA map.
Planting in Cold or Temperate Regions (Zones 3 to 6)
- Plant in full sun to increase flowers and avoid mildew problems. Shrubs need a minimum of 6 hours of full sun daily.
- Plant on the sheltered side of a windbreak. If subjected to cold, dry winds, their leaves and buds dry out and die, especially during winter winds.
Planting in Warm or Hot Regions (Zones 7 to 11)
- Plant in a site that receives afternoon shade, especially in hot areas. In tropical zones, azaleas will bloom in full shade.
How to Plant Rhododendron & Azaleas
- Plant in spring or early fall.
- Space plants 2 to 6 feet apart, depending on their estimated mature size. Dig a hole as deep as the root ball and about twice as wide.
- Set new plants so that their top roots are at soil level or slightly below. If you plant them any deeper, the roots and trunks may rot.
- Fill the hole half full with soil, then water it well to settle the soil before filling it with the remainder of the soil.
Growing
How to Care for Rhododendron & Azaleas
- Mulch plants every spring with 2 to 5 inches of pine bark chips or pine needles to protect shallow roots and retain soil moisture. A lack of water reduces flower bud formation. Read more about using mulch.
- Tip: A common mistake is to create a so-called “mulch volcano,” where mulch is piled heavily around the trunk of the shrub. In fact, this can keep the trunk too wet and encourage rot. Always leave a few inches around the trunk free of mulch.
- See our guide to using mulch.
- Fertilize azaleas and rhododendrons sparingly and only when flower buds swell in the early spring, even if they are fall bloomers. Heavy applications of fertilizer will burn the plants’ roots.
- Water plants during the summer if rainfall is less than 1 inch per week.
- After flowering, deadhead where practical, to promote vegetative growth rather than seed production. Remove dead flowers from rhododendrons carefully; next year’s buds are just under the old heads and will start to develop shortly after flowering.
- Azaleas and rhododendrons may be transplanted at any time during the growing season, but they transplant most successfully during fall or early spring when they are dormant and temperatures are cool.
Winter Care for Rhododendrons
Rhododendrons are shallow-rooted plants; in cold regions, apply several inches of organic mulch around the base. In regions with severe winters, consider wrapping evergreen rhododendrons with burlap in the fall. Cold, dry winds will cause too much moisture evaporation from the leaves, which will wither and die. To help them recover from cold snaps, deeply water rhododendrons if there are warmer days. In the spring, prune out any dead or damaged branches and leaves.
Pruning Rhododendron & Azaleas
- In general, do not prune spring-flowering shrubs such as azaleas and rhododendrons. If you need to reduce height, prune after flowering in the spring.
- Otherwise, just remove dead, damaged, or diseased branches at any time of year.
- On young and old plants, simply snap off spent flower stalks by bending them over until they break away from their stems. Be careful not to damage growth buds at the base of each flower stalk.
Types
There are more than 900 species in the Rhododendron genus, which vary greatly. It would take a whole book to understand this wide world!
You may be interested in joining the American Rhododendron Society, which runs a database with information on more than 2,000 rhododendrons and azaleas. On an annual basis, the society selects a number of rhododendrons to be awarded the Rhododendron of the Year designation, highlighting the best-performing plants for different regions.
Here is a handful of varieties that we think you’ll enjoy:
- ‘Blue Diamond’ is a dwarf evergreen rhododendron that grows to 3 feet. It blooms mid-season with violet-blue flowers. Zones 7 to 9.
- ‘Cecile’ is a vigorous azalea that grows to 7 feet and produces dark salmon-pink buds in mid-season. Zones 5 to 8.
- ‘Hydon Dawn’ is a low-growing rhododendron that actually tolerates full sun. Pale pink flowers bloom in mid-season. Zones 7 to 9.
- ‘Nova Zembla’ is an evergreen rhododendron that grows 5 to 10 feet tall and bears bright red flowers in late midseason. Zones 5 to 8.
- ‘Rosy Lights’ is an azalea that offers extra cold hardiness. It grows to 6 feet and bears deep purple-pink flowers. Zones 3 to 8.
- ‘Purple Gem’ is a dwarf rhododendron that grows to 2 feet and is an early-season bloomer. It bears small, light purple flowers. Excellent in front of a border or in a rock garden. Zones 5 to 8.
Comments
An initial consideration for almost any failure to thrive is soil quality and pH. Rhododendrons and azaleas prefer acidic soil. That's another way of describing the pH, and pH can be checked with an inexpensive soil tester. A good nurseryman/woman or your local extensive service can help you with that, too.
Rhodos and azaleas also like organic material in the soil and organic mulches on top. Give the plants a good dose of aged manure in late fall (or not al all). See more advice above about the conditions that enable rhodos to bloom at their best.
We hope this helps!
There are a number of reasons why rhodos do not bloom.
• not enough light or too much light
• too much fertilizer (especially too much nitrogen, which promotes foliage)
• the age of the plant
• weather: cold weather can kill buds
• the variety: if it came form the seed of a hybrid plant, it will never produce (or produce poor) flowers.
• planted too deep or has soil mounded beneath it. Roots are shallow and they need air; light mulch is adequate, once the plant is set.
• You might also check the pH of the soil (do a test). See above for advice on that.
We hope this helps!
One the face of it, Gordon, your idea sounds reasonable. However, we would also consider making a call to the nursery from which you purchased it. (It sounds like a recent purchase.) They may remember you and/or the plant and be able to give you advice. Some rhododendrons lean toward the shade...you want to be sure of your plant's preference.
Hard water could be the source of the problem. High alkalinity is common in hard water, and rhododendrons like acid, quite the opposite of alkalinity. Have your water tested for its pH, and help the plants with fertilizer (get something specifically for acid-loving plants, such as rhodos and azaleas). Your comment about "any type of soil" is a little suspect here, too, though. Rhodos like acidic soil, so you should test it, too. Peat moss will help to add acidity to the soil (and retain moisture) and aged manure (mixed in in the fall, or not at all!) will help, too. For more on these details and others, see above.
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There are several reasons why plants do not bloom. Re rhodos in particular:
• were they nipped by frost?
• are they too dry/lacking moisture?
• is it getting enough light? Rhodos need a balance of light and shade (there is no specific formula) and cool feet, which is to say they do not like a place where the ground under them gets too warm.
We suggest you also read the care and pruning tips above. You could prune this tree down to the new growth but it behooves you to consider the previous and above before doing anything drastic...if you want to keep the plant. Of course you could prune it a little.
As for fertilizer, these plants like acidic soil; check your soil's pH. It can change over time and perhaps has slipped out of range (see above). Amend as needed. And, spread add aged manure under it (wide, not just at the stem, so it affects the shallow roots) in the fall or not at all—as the saying goes.
We hope this helps!