How to Grow Rhododendrons

Rhododendrons  can be deciduous or evergreen,  although many of the most popular varieties for the garden tend to be evergreen. Rhododendrons are undemanding and easy to grow shrubs, their only essential requirement is an acid soil which is a soil in which the pH is 7.0 or below. As the images above show Rhododendron flowers are lovely showy blooms and attractive to bees as a good source of nectar. In gardens with acid soil, it is easy to grow Rhododendrons and Azaleas as they will thrive on ericaceous soil, but they will not grow well in alkaline soil so it is best to check first. This is not just a case of growing better in acid soil, Rhododendrons simply will not grow in any soil other than acid soil.  Generally Rhododendrons flower from March-May.

It is easy to be put off Rhododendrons, which in recent years have had a bad press, as being a very large shrub swamping other plants. It is correct that the common Rhododendron,  common rhododendron or pontic rhododendron, is considered a menace, and which looks like the image above right. In the wild in the UK this variety of Rhododendron is invasive, out competes native plants and is to be avoided. 

However,  Rhododendrons are a vast group of genus over 900 in all shapes, sizes, and heights which means there is a suitable shrub for all types of gardens from low growing compact varieties to huge tree like shrubs. Rhododendrons come in a wide colour range, pink, purple, yellow, white, red and orange, just about everything. The colours are bright and bold;  a Rhododendron in full bloom is eye catching. Rhododendrons need no real attention other than an acid soil, although most prefer dappled shade. Rhododendrons are originally a woodland plant and so dappled shade is their native conditions, although Rhododendrons are fairly tough and will grow anywhere in the right (acid) soil. If the growing position is very sunny the smaller compact and deciduous varieties will do best. 

It is because Rhododendrons are such a wide genus with many varieties it is important to check the plant label when buying to  check the eventual size, as some are get very large and be thuggish. There are many on the market which are compact, and it is well worth checking the label, to make sure the plant is suitable for the space in your garden as some are huge, small trees really.  

If you are thinking of growing Rhododendrons, but unsure of your soil type, you can do one of two things. You can buy a soil kit to test the Phd of your soil which will tell you if it is acidic: a result of pH 7 below is acid soil, pH7 neutral and pH7+ alkaline soil. Alternately you can check out your neighbour's garden and see what's growing there. If there are Rhododendrons and Azaleas in the neighbourhood, the chances are your soil will be similar.

Spring combination yellow rhododendron, Euonymus and Aquilegia

Scented Rhododendron and Rhododendron combinations

Rhododendrons  are spectacular as single shrub, or massed together and mix well with other shrubs. The image above is a great, bold spring combination with a the strong yellow Rhododendron, combined with the variegated Euonymus fortuneii 'Emerald Gold'  and flowering Aquilegia 'Swan Lavender'  which makes a really bright spring combination.

There are a few scented Rhododendrons which are often the deciduous varieties. R. Fragrantissimum which is only hardy down to -10 and bears white flowers. R.Luteum which has garden merit award, it is a fully hardy deciduous azalea growing up to around 2.5m/8ft. R. Loderi has coral pink flowers, Dufthecke white, Inkarho is evergreen and fragrant with white flowers and finally Antelope which is a sun loving hardy deciduous azalea.  

If Rhododendron is not the shrub for you check out shrubs and bushesspring flowering shrubssummer flowering shrubsshrubs with autumn and winter interest; and evergreen shrubs.

How to Prune Rhododendrons

Some Rhododendrons can get very large over time and out grow their space. Although a very woody shrub it is possible to hard prune Rhododendrons, even quite severely and they will grow back. Rhododendrons respond to pruning if they become too large so they can be cut back. Initially, they make look a bit of an eye sore with bare wood but fairly soon the Rhododendron will produce fresh new growth. 

Rhododendrons respond well to pruning and you can cut back in mid summer after flowering. There is always a risk to the next seasons flowers but after that the shrub will pick up. The same applies if you hard prune, initially it will look decimated as in the images below, but new growth appears and the shrub soon gets re established. This is  helpful if the shrub is too big, or overhanging a path or creating too much shade. Cut back how you want and it will re grow. The image left shows a Rhododendron after a hard prune, centre starting to grow back and image right there is no bare wood visible after a prune.

Rhododendron after being hard pruned

Rhododendron hard pruned

Rhododendron growing back after being hard pruned

Rhododendron growing back after hard prune

Rhododendron grown back after pruning

Rhododendron grown back after pruning

Warning about Rhododendron ponticum

Rhododendron pontiucm -by-eiffel-public-domain-20040617

This is a plant mug shot, and this plant is a thug and carries a huge gardening health warning. This Rhododendron is extremely vigorous and growing out of control in parts of our countryside, such as the Snowdonia national park. Once established it is very difficult to remove. Each plant can produce a large quantity of seed and so it has, and does, escape the garden setting and into the countryside where it is adverse to wildlife and natural flora. There is also a lot of debate about whether Nectar from Rhododendrons, especially R.ponticum is toxic to bees and the answer is complex

How to dead head a Rhododendron

There is a view that Rhododendrons can look untidy after flowering and that dead heading encourages better buds. If you are a keen gardener you can dead head after flowering which is said to encourage better blooms the next year and certainly looks better,  but be careful not to remove the embryo bud forming behind. The important point is not to remove the embryo bud and to be clear what is old bud and new bud. The images below illustrated, first left has the spent flower and the new bud; the second center image shows removing the old bud and right the plant with just the new bud.