Rhododendrons and azaleas have, up until recently, been categorised as a different species but are now considered as simply part of the rhododendron genus. There are some differences between the two, like the fact that rhododendrons tend to always be evergreen whilst azaleas are often deciduous. Rhododendron flowers are also produced in large clusters whilst azalea flowers tend to form in smaller groups at the end of a stem. It is wise therefore, when choosing a rhododendron or azalea to read the notes on the particular variety before purchasing to ensure it is going to suit your requirements. There are thousands of cultivars that come in a variety of colours from the more common purples and pinks through subtle white and off-white shades, to the more vibrant and fiery oranges, reds and yellows. Almost all varieties put on a great display of colour from spring into early summer, with evergreens adding structure and interest throughout the year.
Rhododendron - Image by Jarmila from Pixabay
Where and How to grow:
Regardless of the slight differences between the two, they both require the same conditions and care. Rhododendrons and azaleas are considered to be woodland shrubs and so they prefer a position of dappled shade in the garden and most importantly they require acidic soil. Some may tolerate a more neutral soil but ideally they will thrive in soils that have a ph value of somewhere between 5 and 6. If you are unsure about the acidity of your soil, it is advised that you carry out a soil ph test, which is easily done with a fairly inexpensive ph testing kit or a ph meter.
In the event that you have a more alkaline soil (with a ph above 7) then the best advice is to grow your plants in a container filled with ericaceous compost. You will often hear of ways you can convert your alkaline soil into acid soil, but in reality, whilst not impossible, this is a difficult task and over time the soil will revert back to its alkaline state unless treated continuously.
For those who do have acidic soil, planting Rhododendrons/Azaleas is similar to planting other shrubs with just a few differences if you want to give your plants the best conditions:
- It is advised that you prepare the planting area with some neutral to acidic organic matter such as leaf-mould, composted tree bark or brachen, or decomposing pine needles. Be sure to do this in a wider area than just the size of the pot you intend to plant as this will encourage roots to spread out and help the plant to become better established and more anchored in the soil
- Dig a hole slightly wider than the pot you bought the plant in and no deeper. These plants are surface-rooting and so the roots should only be barely covered.
- Remove the plant from its pot, loosening any roots that may have become pot-bound (it's always good practice to give the pot a good watering an hour or so beforehand).
- The roots will benefit from a dusting of mycorrhizal fungi which will help the plants establish much quicker but be sure to buy the fungi that is specific to ericaceous plants. You can then position your plant and start to backfill the hole, gently firming the plant in then give it a good watering for which you should use rainwater if possible. Tap water tends to be alkaline and so it is much better to use rainwater that has been collected or if this isn't available, add a drop of vinegar to your watering can (just a couple of drops in 5L of water will do).
- Apply a 3 inch mulch of acidic material such as chipped conifer bark, being sure not to compress it too much which will prevent any aeration. This will help keep moisture in the soil and should be replenished every spring whilst the soil is still damp.
Rhododendron & Azalea care:
Rhododendrons and azaleas require moisture, which, generally isn't an issue in Ireland and certainly not up here in the west. In drier areas or in those rare times we have a dry season or 'heatwave', your plants will need to be watered regularly to keep the soil moist. Again, this will really require you to use collected rainwater where possible. Tap water may be OK for a month or two during the summer but your plants will not tolerate continued watering this way, especially if you live in an area where there is hard water - the water will just contain too much calcium which will then starve your plants of much needed iron.
With the right soil and the right conditions, as described above, your plants will really need very little care other than that mulch in spring.
For container grown plants, it is recommended that you repot your plant ever other year in fresh ericaceous compost to prevent browning of the leaves or die-back. You can even put them back in the same pot of you cut back a third of it's roots before repotting. For the years in between, simply replace the top 2 inches of compost. They will also benefit from the addition of a slow release ericaceous feed in spring or alternatively you can use a liquid ericaceous feed, following the manufacturer's instructions.
Other than that you will just need to dead-head your plants, removing any spent flowers and you can prune your plants to tidy them up or restrict their size where necessary.
Ideal companions for your Rhododendrons & Azaleas
The ideal companions for your rhododendrons and azaleas will be those that thrive in similar growing conditions, so other acid loving plants are ideal such as:
- Pieris - these evergreens are ideal for added all year interest and produce clusters of small white urn-shaped flowers in spring that can offer a nice contrast to the more vibrantly coloured flowers of your rhododendrons and azaleas or blend well with white flowering varieties.
- Vaccinium/Blueberries - another acid-lover, these shrubs also produce white flowers in spring and have the added bonus of providing you with delicious fruits in summer and bronze, scarlet and crimson foliage in autumn before leaf-fall.
- Hamamelis/Witch Hazel - another acid lover that produces unusual, spider-like yellow, orange or red flowers (depending on variety) on bare branches in spring.
Rhododendrons and azaleas also pair well with many shrubs that aren't so fussy about soil types such as viburnum, mahonia and enkianthus as well varieties of hydrangea and a wide range of perennials and bulbs that like the dappled shade including ferns, hostas, snowdrops and grape-hyacinths.
Azalea - Image by Ilona Ilyés from Pixabay
A brief note on toxicity
Whilst it is highly unlikely that your pets will be digesting these plants it is worth noting that all parts of azaleas and rhododendrons are toxic to pets and can cause nausea, difficulty breathing and if eaten in large amounts can be fatal for dogs.
Cover Image by Karsten Paulick from Pixabay
