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Lime Tolerant Rhododendrons

Lime Tolerant Rhododendrons

Inkarho Rhododendron
Inkarho Rhododendron

 

Whilst Rhododendrons have been regarded as ericaceous  plants unsuitable for alkaline or limey soils the newly bred Inkarho plants may be an exception.  It is also believed that some species and root stocks are tolerance of more alkaline conditions.

These German branded Rhododendrons have been developed to survive in soil which is less than perfect  for Rhododendrons. They are all grafted onto a stock that is lime tolerant like the old variety Cunningham’s White or R. hirsutum or R. ferrugineum. The root ball tends to be quite large and robust on these varieties and that may account in part for the ability to withstand alkaline soils. Not everyone is impressed with the results attributed to this breeding programme and particularly the reasons for lime intolerance see Non Conformist Rhododendrons by David Rankin  

His ‘suspicion is that there are in fact many more lime-tolerant species than we had been led to believe, or that at least there are tolerant strains. What we want to do next is to see whether these species growing on limestone are able to avoid absorption of calcium by their roots.’

I am happy to have the right soil for most Rhododendrons but here are a couple more pictures from Inkarho off spring.

Rhododendrons, which require a pH between 4.2 and 5.5but lime tolerant types  of root stock can thrive with a pH between 4.5 and 6.5. An added advantage of plants which have been bred on lime-tolerant root stock is that they are stronger on normal soils.

 

new-picture-22

 

RHS suggests other rhododendrons to try on alkaline soil:

R. augustinii (Electra Group) ‘Electra’ AGM
R. ciliatum
R. hippophaeoides
R. ‘Praecox’ AGM
R. triflorum

 

What Kills Rhododendrons

What Kills Rhododendrons

It would be nice if your Rhododendrons were only to die from old age. Rhododendrons are generally long lived shrubs that would then outlive most of us and this article wouldn’t be needed.
However the natural world is not like that and accidents do happen. Gardener inflicted death can be caused by being over protective or trying too hard.

Rhododendron

What Makes a Rhododendron Die

  1. Rhododendrons are fibrous, shallow rooted plants that need good drainage to perform well and excess water is currently the major cause of death. Digging a big planting hole that creates a water sump is the way to drown your Rhododendrons.
  2. Rhododendrons do not have taproots to take a drink, unlike trees. Therefore Rhododendrons need frequent watering particularly when young or if spring is very dry.
  3. Another cause of rhododendron death is the excessive application of fertilizer directly at the base of the trunk of the plant. A good rule of thumb is to fertilize more frequently at lower concentrations rather than one large dose especially for small plants or newly transplanted plants.
  4. A fourth reason for rhododendron death is planting too deep. As indicated earlier, rhododendrons are shallow rooted plants and if buried they will stagnate or even die.
  5. Another reason that rhododendrons die is from cold winter temperatures with deep frozen soils. Most rhododendron can be grown in cold areas but I mulch around tender species.
  6. Not many varieties can survive unprotected all-day sun and some say they ‘are doomed’. In general rhododendrons in extreme climates benefit from filtered light and partial shade but there are some varieties that can stand direct sun.
  7. Sudden oak death fungus Phytophthora ramorum has recently infected Rhododendron ponticum and some container grown plants so this problem is moving up the chart of the causes of dieing.
  8. Fungus that causes ‘die back’ thrives in the same general conditions preferred by most rhododendrons. I am sometimes tempted to use a fungicide.
  9. Physical damage by rabbits, Deer or football playing grand children may cause breakages but should not lead to death.

Frost damaged Rhododendron

None Fatal Rhododendron Problems

Rhododendrons are a hardy species – they need to be coming as most do from the Himalayas
Frost has got to these rhododendron flowers but that is not cold enough to kill the plant.
Dried black buds may be caused by insect damage or water shortage.
Burned tips on this year’s new growth is typically indicative of lack of water as the plant withdraws water from the tips of the new foliage first.

June Rhododendron

Vireya Exotic Rhododendrons

Vireya Exotic Rhododendrons

Just when you have seen enough about Rhododendrons and Azaleas but this is the last Rhodo post for a while
Pink Vireya

Are you interested in scented, colourful, winter flowering exotics? These Rhodoendrons are now seldom grown in the UK but it is easy to acquire the taste for this species that originate in South East Asia.
In Victorian times they were in vogue with over 500 hybrids from half a dozen species. Now there are over 300 recorded species in 7 sections on the wonderful Vireya web site. …

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Grow Bright Azaleas

Grow Bright Azaleas

A lazier shrub with exciting blossom I have yet to find.
Azalea

How do you tell an Azalea from a Rhododendron? Most Azaleas have only 5 or 6 stamen while most rhododendrons have 10 stamen. Azalea leaves tend to be thinner, softer and more pointed than rhododendron leaves.
In a subjective way I think Azaleas produce more flower cover per plant.

Tips for Growing Azaleas

  • Azaleas are relatively pest-free  and easy to grow plants but may need a fungal spray if leaves are attacked in spring.
  • Azaleas like some shade  but deciduous varieties do well in full sun. Sun can produce more compact plants with more blooms but not as long lasting.

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Azaleas for your Home

Azaleas for your Home

A grand house plant that will last and last if you give it soft water.

Azaleas

Rhododendron simsii or indoor azaleas produce large funnel shaped flowers in a range of bright colours almost gaudy.

  • They dislike warm conditions and are more suited to a cool room or porch.
  • Buy in tight bud and they will open progressively indoors.
  • Plants need an acidic, loam compost and will benefit from misting with water on a daily basis until their buds start to show colour.
  • Keep plant roots just moist at all times and water with soft water to keep plants healthy.
  • During summer they can go outside but keep the moist.
  • Flowers are better when the plant is root bound in a pot.

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