Flowers, Gardening, Gardens, Grow Your Own, How To, Planting, Plants, Watering

Rhododendrons and azaleas usually bear their spectacular, large, often scented flowers in spring – but do you know the difference between the two?

Well, both are in the genus Rhododendron –  but azaleas can be distinguished by having five stamens per flower (one per lobe), whereas rhododendrons have 10 or more (two per lobe). Azaleas can be deciduous or evergreen but rhododendrons are all evergreen. Finally there is a difference in size. Azaleas are small to medium shrubs – rhododendrons range from prostrate shrubs to huge trees.

Within this guide you will find information about some of the different varieties of rhododendron and azaleas, as well as information about how to successfully plant and maintain your own.

Main Species

There are more than 28,000 rhododendron or azalea hybrids, as the plants readily cross breed. However, here are the most popular varieties for gardeners:

  • Hybrids or hardy hybrids: What gardeners would consider a ‘traditional’ rhododendron with large flower trusses, some scented, blooming anywhere between January until July – often growing very large.
  • Dwarf rhododendrons: Mainly alpine varieties, ranging from 20cm-80cm, flowering in April.
  • Yakushimanum: Mound-shaped plants reaching 80-100cm, often with unusual leaves. Many brilliant flower colours available.
  • Williamsianum: Unusual rounded leaves, 80-100cm.
  • Deciduous azaleas: Sun lovers, growing up to 150cm, often scented, (especially R. luteum) with rich autumn foliage. They can be divided into Species (Sciadorhodion, Pentanthera, Rhodora, Sinensi or Brachycalyx); Ghent (the oldest hybrid group with multiple small flowers); Knaphill (large flowered hybrids, some of which are scented); Mollis (earlier flowering, more compact and spreading); Rustica (small double flowers, some scented). Other deciduous azaleas include Pratt hybrids, viscosum, occidentale and the Northern Lights series.
  • Evergreen azaleas: Small, slow-growers, suitable for pots, up to 75cm, some are prostrate in habit, with autumn colour. Flowering season is usually May.

Planting

Choose a sheltered site with dappled shade, however, dwarf alpine species will tolerate full sun. Avoid sites exposed to early morning sun in spring, as this may damage frosted flowers.

The most important factor deciding whether rhododendrons or azaleas will grow well in your garden is the pH of your soil. They must have moist but well-drained, acid soil between pH 5.0 and 6.0 that is rich in organic matter. Reducing soil pH is not easy.

October or March/April are the best times for planting – dig in acidic organic matter before you begin (leafmould, rotting pine needles or composted bracken will work well). Don’t just concentrate on the planting hole – mix well around the surrounding soil. Don’t plant deeply, as rhododendrons are surface rooters. Apply a loose 8cm mulch of acidic organic material and water well to finish.

Care

To keep your plants performing at their best, in spring, apply slow-release ericaceous fertiliser and renew the acidic mulch and keep well watered.

Rhododendrons grow best in areas of high rainfall, which is naturally slightly acidic. Using tap water, especially in hard water districts, is not good for the plant as it contains too much calcium which reduces the acidity around the plant’s roots. However, if rain water runs out, tap water is OK to use for a month or so in summer.

Rhododendrons don’t require pruning apart from removing dead wood and deadheading if practical. If the plant outgrows its space, cutting back is tolerated best from deciduous azaleas and rough-barked rhododendrons. After cutting back, mulch, feed and keep well watered.

Growing in Containers

If you have alkaline soil, grow rhododendrons and azaleas as container plants. Use ericaceous loam-based compost and repot every other year into fresh compost in spring. When not fully repotting, top dress the top 5cm of growing medium with fresh compost.

Common Problems

Most problems with rhododendrons and azaleas stem from the soil being too alkaline, drought or other extreme weather conditions. Here are signs to look out for:

  • Non-flowering and bud drop: Flower buds actually start forming in late summer – dry conditions at this time can lead to a total bud formation failure or a partial formation, causing buds to dry up and dropping unopened in spring. Mulch and water thoroughly and regularly during dry periods in summer.
  • Leaf drop: Older leaves droop and roll, then drop off, following extreme moisture conditions – drought or waterlogging. Newer leaves show browning at the leaf tip or edge. However, it is normal for the shrub to shed some older leaves in spring and summer.
  • Leaf droop: Usually a response to severe cold, but they usually recover.
  • Leaf scorch/flower damage: Often caused by windy, cold or wet weather.
  • Yellowing foliage: Caused by nutrient deficiency known as chlorosis, an iron deficiency caused by high alkalinity in the soil.
  • Pests: Vine weevil can be a nuisance for container-grown plants, as can rhododendron leafhopper and scale insects.
  • Diseases: Relatively uncommon are bud blast, azalea gall and honey fungus.

Composting, Garden Design, Garden Edging, Gardening, How To, Insects, Liam, Make over, Planting, Trees

In this step-by-step guide we’ll not only show you how to mulch but explain the different kinds and what will work best for your plants and garden. Mulches are a thin layer of organic or inorganic material placed over a bed or the soil surrounding plants. The more attractive ones may grab your attention and look like a great addition to formal landscaping, but the practical uses are vast. 

Mulches are used primarily to improve the soil around plants, reduce weeds, increase fertility, help the retention of moisture and during winter can protect the roots of the plant from damaging frosts. Using the right mulch for your plants can help eliminate the need for chemical pesticides and fertilisers which is fantastic for your garden’s biodiversity. This all contributes to a healthy, great looking garden you can be proud of.

Now that Autumn is approaching it is the perfect time to start planning!

The Types:

You can roughly separate the different types of mulch into two categories; organic and inorganic.

Organic mulches are best for improving the fertility and overall structure of the soil. Over time the mulch will degrade and replenish the soils nutrients including nitrogen, potassium and phosphorus. Organic material also promotes biodiversity and encourages insects such as worms and spiders which will actually keep pests at bay while further enriching the quality of your soil.

For this reason an organic mulch is fantastic for plants try to establish themselves or are just generally hungry. Roses for example love a good organic mulch of well-rotted manure. More on this to follow.

Inorganic mulches are used to protect the soil around the plant and can also have an aesthetic edge to them. The benefits include locking in water to the soil, keeping weeds at bay and unlike some organic mulches it won’t wash away which is brilliant if you are planting on a slope.

Bark and Wood-Chippings

Here is a mulch which is attractive but also helps improve your soil’s nutrients and structure as it rots down. It also allows water to flow through it without binding throughout the year and really is a fantastic for pretty much all plants and circumstances. The only issue with it is that it is difficult to move or work around and so is best for around trees where you won’t be doing any more planting. Bark and wood-chippings will last you through the year and maybe even two depending on the grade, see how far it has broken down and replace if necessary.

Wood Chippings Mulch

Leaf-Mould

Leaf-mould is arguably the most nutritious and nature-friendly mulch you can apply. Pretty much every plant loves it and what’s more it can be completely free! It may not look like the most attractive mulch but apply in Autumn and by spring it will have blended in with and really enriched your soil. The only major drawback is that leaves do take some while to decompose and if you plan to DIY this is something you plan for a year in advance.

Collect as many leaves as possible in black bags and cut some small holes to let the air in. Ensure the leaves are thoroughly wet as leaves break down through fungi. Come next Autumn you’ll have some of the finest and richest mulch money can buy… not that you have to spend a penny! Of course, leaf mould is available to purchase in fairly substantial bulks.

Compost

There are two main reasons why compost can make a great mulch: 1) It is packed full of nutrients ready to leach down into the soil and 2) It is something you can make yourself free of charge. Additionally it helps with keeping the soil moist and fending off weeds. One thing to look out for however is that no weeds have made their way into the compost as these will simply sprout up from the compost and steal your plants nutrients.

Manure

As I’ve briefly mentioned before, when it comes to roses and other phosphate hungry plants nothing compares to some well-rotted manure. Like a compost that has gone through a far more strenuous decomposition process it is packed full of nutrients and its dense texture protects the roots and keeps the water locked in. It is also a really great mulch for trees and shrubs although to prevent waterlogging it may be worth mixing with some sand to allow for greater drainage.

Manure – As is Comes From a Stable or Farm

Gravel, Slate and Stone Chippings

There really isn’t a great difference here between them as you will want roughly the same thickness of layers. Stone mulches are fantastic for drainage and keep the soil underneath moist. It is also brilliant for retaining heat and so should be used for plants that are used to very hot conditions and can be worked into a Mediterranean themed garden well. Overall many stone mulches look fantastic and can maintain a pristine look for formal garden structures. They do not however add any nutrients to the soil and can become too hot during summer for more tender plants and young trees.

Rainbow Foras Tumbles Coloured Pebbles

When to Mulch

The best time to apply a mulch is in Autumn, as you come into bare-root season, and spring. You will need to apply the mulch when the ground is relatively warm and moist, avoid periods when it is frozen or waterlogged. When the ground is good to dig and plant, it will be good to mulch which is very handy!

How to Mulch

  • Before you apply your mulch first you have to prepare the soil. Clear the ground of any weeds and give it a watering if the soil appears too dry.
  • If you are reapplying a mulch now is a good time to break up any old layers which may have matted to allow better water penetration.
  • Then cover the ground in a layer of mulch roughly 2 inches thick. Avoid mulching right up to the stems of plants and trees as this can cause them to become soft and rot.
  • Level out with a rake to an even finish. This is imperative, some people mulch little mounds, especially around trees. This will cause the bottom of the trunk to grow soft and rot while also drawing water away from the roots.
  • If you noticed that your mulch has matted over the year and become a hard layer, simply break  and fluff up a bit.

You can apply a fertiliser on top of the mulch through the year if you wish. Follow these rules and you should be all set!

Liam at PrimroseLiam works in the buying team at Primrose. He is passionate about studying other cultures, especially their history. A lover of sports his favourite pass-time is football, either playing or watching it! In the garden Liam is particularly interested in growing your own food.

See all of Liam’s posts.

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