Rhododendron and Azalea Groups
The question we get asked the most is “what is the difference between a Rhododendron and an Azalea?” Here we will try to enlighten you to the different Rhododendron and Azalea Groups as well as answering that burning question!
All Azaleas are actually Rhododendrons BUT not all Rhododendrons are Azaleas.
Confused? Rhododendron is a genus (a group of plants with shared characteristics) and Azaleas are a group within that genus, rather than forming a genus of their own.
Still with me? This is how you distinguish differences:
- An Azalea has 5 stamens while other Rhododendrons have 10 or more
- Azaleas may be deciduous or evergreen and other Rhododendrons are all evergreen
- Azaleas are small to medium shrubs but other Rhododendrons range from prostrate shrubs to trees
One thing we do know, is that they all require the same conditions and cultural treatment for healthy growth!
So, within the Rhododendron genus, to help our customers with their selections we have the following categories:
Dwarf
These are mainly alpine varieties, and range from very tiny plants from 20cm up to 80cm after ten years. OK, they can be species or hybrids. They mainly flower in April, look great planted in groups of 3 or 5 and are perfect for smaller spaces. Great for welcoming the Spring and stunning in rock gardens.
yakushimanum
This group form mound shaped plants of 80 to 100cm after 10 years. They are ideal for the front of border or for more formal situations in containers. Often they have interesting foliage. The hybrids that we grow in this group hail from R. yakushimanum ‘Koichiro Wada’ which is probably one of our favourite plants.
williamsianum
This group have unusual rounded leaves and make an interesting foliage addition. They are relatively small, 80 to 100cm after 10 years. Again they are useful for the front of border or in containers. R. williamsianum is the parent of these hybrids.
Small leaved (cinnabarina and triflora)
Highly under-rated in our opinion! Not grown by many nurseries, these are mainly species plants (cinnabarina and triflora) and grow 75 to 150cm in 10 years. They often have an upright habit, soft foliage and stunning bell shaped flowers.
Hybrids or Hardy Hybrids (tall Rhododendrons)
Called hybrids because they have been promiscuous (or their breeders have) and different varieties have been crossed to produce the most beautiful blooms. These are your traditional Rhododendron with large flower trusses, some blooming from January until July. Some are ideal for hedging/screening and all will sit beautifully in borders. Did I mention that some are also scented?
Inkarho or Lime Tolerant Rhododendrons
These are the plants which we featured at 2011 RHS Chelsea Flower Show, and were mentioned by David on the BBC2 Chelsea Preview. The revolutionary new "Inkarho" lime tolerant rootstock is particularly recommended for growing Rhododendrons on neutral clay soils, up to pH7.5. This patented rootstock was developed from a Rhododendron growing in a German lime quarry, and has been the subject of an extensive 20 year breeding and testing programme. These plants are grown under licence in Germany, and enable choice hardy hybrids and yakushimanum varieties to be grafted on the rootstock and grown in a much wider range of soil types than ever before. So now you can grow a Rhododendron almost anywhere!
Species
Here we do have the widest range of species Rhododendrons in the country! We aim to propagate these plants from collectors’ seeds or recognised good forms. These are the true Rhododendrons, many collected from the Himalayas by our collector friends. You will notice that Species Rhododendron names are usually shown in italics and often are of latin origin (they also don’t start with a capital letter). We love our species plants and you will see that many of them have the collector seed number in the name or the description of the plant. This identifies where the plant was collected from, when and by whom. All very exciting and of particular interest to collectors.
Big Leaved Species
These are the ‘show offs’ in our Rhododendron world. Species plants, architectural with huge leaves up to 60cm long. As mentioned previously, many of these have collector seed numbers, so have the provenance that you would expect from us. They love woodland settings and do need the best sheltered positions to thrive. But thrive they will, growing up to 5m tall and flowering too after around 6 years.
Deciduous Azaleas
Deciduous, so they do drop their leaves in the winter. But they make a dazzling display, particularly in yellows and oranges. They are tough and fast growing up to 150cm and many of them are scented. Did we mention many have rich Autumn foliage and they mainly like sun? Deciduous Azaleas can be divided into different groups all with distinct characteristics:
Species: Many are scented particularly R. luteum.
Ghent: This is the oldest of the hybrid groups and they usually have small flowers.
Knaphill: Flamboyant hybrids, some of which are scented. These were originally developed at Knaphill Nursery near Woking in Surrey (hence the name) and Exbury.
There are many Knaphill hybrids flowering from late May to mid June.
Mollis: These flower a little earlier than the Knaphill hybrids. A little more compact and spreading and reasonably heat tolerant. Not so widely available.
Evergreen Azaleas
Great plants that are happy in a window box or front of border in a large garden. Most grow 60-75cm in 10 years. Some are prostrate in habit, so excellent for cascading over walls. With small leaves, many have lovely autumn colour for that extra bonus. They mainly flower in May, with some later exceptions. There are no yellow Evergreen Azaleas (that we know of!)