What to plant now: May – Rhododendrons and Azaleas

At this time of year, Rhododendrons and their close relatives, Azaleas, are really putting on a spectacular show, which should last right through May. For some great local examples, why not visit Exbury or Furzey Gardens, to see them in all their elegant abundance? At public gardens like these, the Rhododendrons may well be enormous; they are naturally woodland shrubs which is why they do so well in environments like the New Forest. However, there are varieties which can offer the same spectacle on a more domestic scale. And now is a great time to think about planting one in your garden!

What's the difference between a Rhododendron and a Azalea?

It’s a frequent question as both species look quite similar but, largely, it’s a matter of size. Rhododendrons tend to be larger shrubs, with similarly large flowers and leaves, and are evergreen. By contrast, Azaleas tend to have smaller leaves and flowers, they can be evergreen or deciduous, and can come in even more eye-popping colours. Some Azaleas are scented too.

For a smaller garden, therefore, you might want to choose either an Azalea or a dwarf variety Rhododendron. If you have a little more space, and are happy to give it height too, perhaps a Rhododendron might suit better.

Before you plant

Your soil: Because they are woodland plants, used to living on decaying plant matter, both Rhododendrons and Azaleas prefer an acidic but free-draining soil. In our area, your garden could be acidic already; Hampshire ranges from loamy, slightly acidic soils in coastal areas to limey, more alkaline soils on hills and inland. If you’re not sure, it’s worth buying a soil testing kit (from just £2.99 in our Titchfield store) to check. A pH reading of between 5 and 6 is ideal. If your soil is neutral or alkaline, the good news is that Rhododendrons and Azaleas can grow well in pots. Just ensure you buy a peat-free ericaceous (acidic) compost to plant it in.

Your aspect: again, because both species are woodland plants, they will prefer a site that gives them some dappled shade during the middle of the day. Avoid deep shade and areas that are prone to frosts or cold winds. A sheltered spot that catches the evening sun would be ideal. (There are some varieties of dwarf alpine Rhododendron which can tolerate full sun as long as their soil does not dry out completely).

Planting

First, dig your hole. All Rhododendrons are surface-rooting so you don’t have to dig anything too deep. However, to give your plant the best start, work in some organic matter to the hole. Homemade leaf-mould, decomposing pine needles and composted bracken or tree bark make ideal, naturally acidic materials for this. Fork it in well, don’t just put a layer at the bottom.

Then you can add your plant. Knock it out of its pot and give any visible roots a tug away from the root ball, to encourage them to venture out into the surrounding soil. Check the plant is orientated as you want it before back-filling the hole with soil or organic matter. Firm it in gently with your heel and then give it a really good watering, to ensure the roots are making good contact with the soil.

If you’re planting in a pot, the same principle applies. Add some organic, acidic material if you can, to help boost your ericaceous compost. Ensure the plant isn’t too deeply buried, then back fill and water well.

After care

Rhododendrons grow best in areas where there is plenty of rain so you can’t overdo your watering! However, be aware that rainwater is the best thing to use. Most of Hampshire has pretty hard water, with lots of calcium in it, so using tap water can reduce the acidity of your soil, to the detriment of your Rhododendron or Azalea. One tip, if your water butts run out during a dry summer, is to save your cold tea. The mild acidity of tea can help to counteract the effects of having to use tap water for a short period.

Rhododendrons and Azaleas don’t need much feeding but would welcome an annual boost. In the wild, in a forest, they would get a fresh ‘top-dressing’ off fallen leaves each year to feed on so we can emulate that in our gardens. Each spring, a mulch of chipped conifer bark or other organic material should be applied to a depth of about 3 inches (7.5cm) around the base. Don’t pack it down, you want to allow air and water in, and don’t push it tight up to the main stem, for the same reasons. If you don’t have anything to mulch with, or if your plant is in a container where the soil will become exhausted more quickly, consider a general fertiliser (like blood, fish and bone) once in early spring and then again in summer. If your plant is in a pot, it is worth re-potting it every few years, even if you put it back into the same pot, just to replenish the soil and ensure the acidity remains.

Pruning

Rhododendrons and Azaleas don’t need regular pruning; you can just trim them to shape as needed. It’s best to wait until after they have flowered to do this, so you don’t lose any of their display, but you can cut them at any time. Deadheading any spent flowers will help ensure the plant puts its energy into new growth or flowers, rather than producing seeds.

Many larger Rhododendrons will respond to a hard cutting back with vigorous new growth so, if you have inherited any older, straggling specimen, this can be one way to get it back on form.

Potential problems

Rhododendrons and Azaleas are fairly hardy plants and aren’t usually subject to many pests or diseases. What has the potential to affect the look of the plant more are extremes of weather: leaves may droop if it gets severely cold but are likely to recover with the temperature. If there has been drought, both leaves and flowers may drop, so keep up with the watering.

Rhododendrons actually start to form their flower buds in the late summer and autumn for next year (similar to camellia). Dry periods during this time can cause those buds to drop so, again, keep up with the watering if you’re in any doubt.

Further reading this month:
The five jobs in your garden we’d recommend you do in May
Caring for your garden while you’re away
Your guide to summer bedding plants
Choosing the right plants for pond
Great uses for gravel or chippings in your garden
The benefits of ground cover planting

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What to plant now: May – Rhododendrons and Azaleas

What's the difference between a Rhododendron and a Azalea?

Before you plant

Planting

After care

Pruning

Potential problems

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