Rhododendrons and Azaleas

RHODODENDRONS AND AZALEAS

The first rhododendron I came across was R. praecox growing in a large drift in a bed of pure leafmould. This was at Dawson Park in 1960 when the park was in its early years and was not much more than a playing field with a few interesting plants to relieve the boredom. I won’t ever forget my first two years apprenticeship training, digging drains all winter at Dawson.  The highlight of the year was when that rhododendron flowered and that only lasted a couple of weeks, but it must have made an impact on me as I have never been without my R. praecox. It is one of the first to flower usually in March or early April but only if there are no frosts to shrivel up the delicate mauve flowers.

The following year I was working at Camperdown Park where mature rhododendrons grew all over the place. Training trips in spring arranged for the apprentices by our tutor Walter Gilmore took us to Edinburgh Botanical Gardens and Crarae Gardens where both Rhodos and Azaleas are grown on a massive scale but to perfection. I was hooked for life. Parks training helped me understand the range from the tall varieties to the dwarf evergreens and the deciduous azaleas, and that first bed at Dawson growing in pure leafmould made me realise the importance of giving them the correct type of acidic soil.

Today we do not have to go too far to see them in all their glory growing in natural surroundings covering the whole spring season. The gardens at Glendoick are now world famous as the place to visit to see hundreds of different rhodos, azaleas, camellias and numerous other woodland plants growing in a natural setting of a Scottish glen complete with a burn and waterfalls.

History

No article on rhododendrons and azaleas would be complete without some reference to the massive contribution made by several generations of the Cox family.

In the early nineteenth century the Cox family started a textile business in Lochee. This was consolidated by four Cox brothers in 1841 and the factory at Camperdown Works was reputed to be the biggest jute factory in the world employing 5000 people. Alfred Cox bought Glendoick House and estate in 1899. His son Euan, educated at Rugby and Cambridge, got a taste for the good life while working in London and had little enthusiasm to return to the jute business in Dundee.

A chance meeting in London with the plant explorer Reginald Farrer led Euan to join him in his first plant collecting expedition to Burma in 1919. The trip was a great success and many new rhododendrons and other plants were introduced. Euan loved to write about the new plants being introduced from all over the world and founded a bookshop in London. However this got bombed during the war and Euan returned to Scotland to help run the family jute business. He started to develop the gardens around Glendoick with his new seedlings from his expedition. He also subscribed to other expeditions and received many new plant introductions. A nursery was started with new plants acquired from other collections. Then his son Peter started to go on plant collecting expeditions to Turkey, India then China in 1981. The garden at Glendoick expanded up the burn.

The rhododendron nursery was established in 1953 and the garden centre in 1973.

Peter’s son Kenneth has maintained the family traditions with 9 plant collecting expeditions and written many horticultural books. Peter and Kenneth have been breeding rhododendrons for over 50 years to produce plants suited to small gardens and the Scottish climate.

For the full and fascinating story of Glendoick, the Cox family, and their involvement with rhododendrons and plant exploration, check out the website at www.glendoick.com.

Types and varieties

Most Rhododendrons are evergreen but the Azaleas may be evergreen or deciduous. They come in all sizes from a few inches tall to small tree sizes given time. Many of the deciduous azaleas, eg A. luteum are scented. The flowering season normally runs from April to June, but changes due to weather pattern at the time, and there is always a few types that will flower early or later throughout the summer. R. praecox can flower in late March but the flowers are not frost hardy so can get wiped out in a bad year.

If you have a large garden you can indulge some of the taller growing varieties such as Cynthia, a vivid scarlet, Pink Pearl, or Horizon Monarch a yellow with red buds.

For smaller gardens try Nancy Evans, a deep yellow, or Elizabeth, a brilliant red that has been a favourite for years.

Azaleas tend to flower a bit later, but many have an exotic woodland scent and orange flowers such as Gibraltar. Klondyke is a brilliant yellow and there are numerous others in reds, pinks, mauves and white.

Dwarf evergreen azaleas (Japanese azaleas) may only grow a couple of feet or so after ten years, but they are perfect for mass planting for ground cover. They are also very easy to propagate from cuttings. Glendoick have bred numerous new varieties in colours including pink, purple, scarlet, white, orange and crimson.

Site soil and planting

Most Rhododendrons and azaleas flower better in full sun in Scotland as we don’t suffer too many very hot summers. They associate well as woodland fringe plants with a backdrop of birch, rowan, pine, spruce or if you wish a flowering tree choose a cherry or Eucryphia Rostrevor. However make sure they are not shaded by the canopy.

An acid soil is a must with all of these plants. Fortunately most soils in this area are naturally acidic, but may have been limed for previous crops. They like a free draining soil that can hold moisture. Soils can be improved by digging in plenty of leafmould, composted bark, garden compost, pine needles or peat. Acidity can be improved by using sulphur chips and a pre planting light dressing of sulphate of ammonia and sulphate of iron, but not after planting as they may scorch young leaves.

Plant rootballed plants in the dormant season, but containerised bushes can be planted at any time provided they are always kept moist. Do not plant deep and any mulch should only be quite shallow as the fine surface roots do not like getting buried.

Rhododendrons and azaleas do not need much feeding, so a light annual mulch will be quite enough.

Pests and diseases

Mildew may be a problem on a few varieties, (Elizabeth is prone) but can be controlled with a fungicide used for rose mildew.

Azalea leaf gall, exobasidium, can be a problem on the Japanese evergreen dwarf azaleas. Pick off and destroy any galls as soon as you see them.

Vine weevil adults cut notches around leaves and can girdle the stem just above ground level. They produce white grubs that eat the roots.

Lime induced chlorosis is only a problem where the soil is not acidic enough.

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Herbaceous and border plants

 HERBACEOUS AND BORDER PLANTS

The garden border has evolved over many years as the place around the house to grow herbs for culinary use, flowers to cut for the home and grow a few colourful favourite plants. Plant explorers brought back new plants to try out and slowly the variety of border plants increased in range. These  can include shrubs, roses, herbaceous plants, bulbs, climbers, ground cover, and anything else that happens to be popular at the time. Often in the early years before plants get established any bare patches can be filled with bedding plants and annuals from seed sown each year.

Borders next to buildings are often designed to link the hard building structure into a soft landscape, but with minimal maintenance in mind. Evergreen ground cover including conifers, are favourite and if the ground is on a slope choose plants that can bind the soil surface to prevent erosion such as flag Iris and Shasta daisies.

Design

Borders are usually long and narrow to be viewed from the front with a solid and usually permanent backing. This may be the house wall, a fence or hedge. Although it is natural to have the taller plants at the rear and short ones at the front, try to vary this to give variety of height.

Each plant will have its own season from the Doronicums and Pulmonaria flowering in early April, Delphiniums in mid summer, to the Michaelmas Daisies in September and October. It is better to try and group plants together in their season to increase the impact, and choose plants that blend well together by height, variety of foliage shape or colour. Good combinations include flag Iris with Oriental Poppies and Pyrethrum, try day lilies with Lavender in adjacent drifts, Delphiniums and Phlox are excellent together for height and colour and at the end of the summer into autumn try Anemone Honorine Jobert with a range of Asters, (Michaelmas daisies). At ground cover height, the black grass Ophiopogon is dense enough to smother weeds and when underplanted with white snowdrops is the perfect combination for late winter.

Where ever a plant is a late starter, under plant it with early flowering bulbs such as snowdrops or crocus. Plants that have a very short season such as Pulmonaria can be mixed with Cyclamen hederifolium which begins to grow and flower in late summer and then retains its foliage all winter.

If the border is in shade or partial shade select appropriate plants such as colombines, (Aquilegia), Hostas, Trilliums, Meconopsis, Epimedium, and Primulas, Bergenia, Lamium and Persicaria for ground cover.

If the border is free standing and is not backed by a building, a hedge at the back can help to define its shape, give shelter from strong winds, add colour and give a green background to the plants when in flower.

If the back of the border is a wall or fence it could create an ideal spot for a climber to give added height.

Soil preparation and planting

Borders are often planted up in the autumn so ground preparation is normal in late summer. If the soil needs a lot of amelioration, add a fair bit of garden compost, dig it in then sow a crop of mustard in spring. Dig it in when it comes into flower but before it sets seeds.  Allow it about a month before planting so the mustard is beginning to rot down and open up the soil. Make sure the soil is firmed and raked level and water if necessary before planting. Water again after planting.

Order plants well in advance as often the more popular ones sell out quickly. Your local garden centres will stock most of your needs, but it may be necessary to go to specialist growers for the best varieties. Blackmore and Langdon in Bath specialise in Delphiniums, Phlox and Aquilegia, and Claire Austin in Shropshire specialises in hardy plants. She has some terrific varieties of flag Iris, Daylilies and Oriental Poppies. They both have websites.

Most plants display best when planted in bold drifts.

 

Border plants

These tend to be lower growing than the majority of herbaceous plants, and may not die down in winter such as border carnations and Pinks, Lavender, Rosemary, Kniphofia, Sedum and Bergenia.

They add interest in the winter months when other herbaceous plants are dormant and have died back to ground level. Many rock garden plants can be added to the front of borders to soften edges such as the Delosperma, a succulent sun loving plant packed with yellow flowers in May and grows quickly, though no higher than three inches.

Flag Iris have always been my favourite. They are so easy to grow and come in some fantastic colours, though you need to buy from the specialists to see a good range. Daylilies also have a wide range of fantastic colours that will brighten up any border.

Herbaceous plants

True herbaceous plants die down in winter, but they can grow very fast and there is always something in flower from April till the frosts come the following winter.

My season starts with the blue Pulmonaria and yellow Doronicums in April, then the Himalayan blue poppies and Euphorbias in late April or early May.

Soon there is a rush as the Peonies, Pyrethrums, flag Iris, Colombines, Campanulas, and Oriental poppies enjoy the warm weather.

As they finish, the summer flowers take centre stage with Phlox, Delphiniums, Daylilies and Geraniums.

Autumn is the time for the Michaelmas daisies, Agapanthus, Kniphofia and Anemone Honorine Jobert. Most of these plants need to be in a large group to have full impact.

Bulbs

Spring flowering snowdrops, aconites and crocus are perfect in any spare space, and even narcissus, tulips and hyacinths can be found a spot. Many drifts of low growing plants will not mind a few summer flowering lilies planted at their feet.

Maintenance

Wherever possible I tend to only grow those plants than can stand up without needing support, but some essential types such as the Delphiniums will require staking. Weeds are usually only a problem early on as once the plants grow they will soon smother out any weeds.

After three or four years some clumps will require dividing and replanting.

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A Blaze of Colour

 SUMMER HANGING BASKETS AND TUBS

The garden is now at its peak for spring flower impact. Wallflowers, pansies, polyanthus and all types of tulips are in full bloom and the dry warm sunny weather has brought them to perfection.

However this is the spring display and the summer flowering plants are all growing nicely, ready to take over in a few weeks time.

This is when we start to prepare the hanging baskets, tubs, troughs, window boxes and other containers used to show off the summer bedding plants. I like to have mine established with the first flowers showing before I put them in place. I keep a double set of baskets and pots as the spring and summer bedding plants overlap each other.

Spring flowering pansies can continue flowering to the middle of summer, but although they get replaced by the summer bedding plants, the pansies can either be left somewhere to continue their display, or gently removed from their containers and planted at the front of a garden border.

Tulip, daffodil, crocus and hyacinth bulbs used in the spring display tubs can be reused to brighten up other parts of the garden the following year. All my shrub borders, winter garden and fruit trees get underplanted with extra bulbs every year from the tubs. Even my outdoor grape vine which doesn’t get a canopy of leaves till mid May is in a flower border full of spring bulbs.

My mini orchard of culinary and dessert apples and plums has a show of daffodils, then tulips before it becomes the bluebell woodland glade, then in summer the lilies take over. The fruit trees are very happy with this underplanting of flowering bulbs.

Suitable containers

Hanging baskets come in a range of sizes. I find that a 14 to 16 inch diameter, (35 to 40 cms. for younger gardeners) is about right for the normal urban garden. A larger one will have more impact, but will need really solid and sturdy wall brackets to hold the weight. Good wire baskets are available in all garden centres. Some come with a liner, but I find the best and cheapest liner is an old polythene compost bag turned inside out. I just push it into the basket, put in some compost then trim the top. Remember to keep the black side showing on the outside as you do not really want pictorial compost information competing with the flowers.

A good basket will eventually be smothered in foliage and flowers, so to get a quick all round effect plant some bedding plants into the sides of the basket as you fill it up. Cut slots in the polythene liner and push the plants through gently.

A hanging basket is quite heavy after watering so make sure your wall bracket support is strong enough to take the weight and is well screwed into the wall.

Tubs also come in all sizes from six inches to a couple of feet across. Avoid any that have a small diameter base related to a wide top, as it is likely to blow over as soon as we get a strong wind. It is also a good practise to place a brick or large rock in the bottom to add weight to stop it toppling over. The larger tubs are excellent for specimen begonias, Brugmansia, (Angel Trumpets), Agapanthus (blue African Lily), Canna or an exotic palm tree while still small. Plastic containers may be cheap and will hold water better, but they are very light and easy to topple over if the plants get too big.

Window boxes are less common today, but a strong plastic one is more preferable being lighter and it will need to be very securely attached to the wall at window sill level. Select plants that are trailing or don’t grow too tall if windows need to open outwards.

Unusual containers

Plants can be attractively displayed in all sorts of containers from old garden boots, buckets, rusty wheelbarrows and even colourfully painted old tyres. A few years back we were upgrading our bathroom and had ordered new units. The supplier sent a new toilet with the wrong pipe fittings so had to be replaced. It was too much trouble to collect the wrong one so he told us to dispose of it. I dumped it outside by the bins awaiting disposal. It was spotted by one of my art class students who was a very keen gardener, and liked to try things unusual. She was delighted to find a home for our unwanted brand new loo as a decorative floral feature in her garden.

Good bedding plants

Garden centres stock a wide range of suitable bedding plants from early March onwards. Many have come directly from greenhouses and may not be hardy so be wary and only buy in March if you have a greenhouse to grow on. At this time of year most plants are now hardy.

You can buy plants as small plugs and grow them on into bigger plants.

Growing your own plants from seed or cuttings is a cheaper way to produce good plants, but you need space and time.

I have been growing my own geraniums from cuttings every year for over ten years and my own tuberous begonias for over fifteen years. They are both very easy. Impatiens (Busy Lizzie) is also very easy but when overwintered in the house in a window sill it is prone to attacks of greenfly and red spider. These are not easy to control for the amateur as chemicals available in garden centres are now very limited and not very strong. After spraying, greenfly and red spider just sulk for a few days with a mild headache then a week later they are ready to feed and party again.

My other favourites include Nemesia Carnival, Petunias, especially the blue scented one, trailing Lobelia, Fuchsias especially Swingtime and African Marigolds for larger tubs.

However it is always worth trying a few different plants, so include some Salvias, Livingston Daisies, Verbena, dwarf Phlox, Ageratum, Antirrhinum, and bedding annual carnations.

Something different

Edible landscapes are becoming very popular and useful to introduce children to gardening as they have more interest to them than flowers. They just love popping things into their mouths.

Cherry tomatoes grown as a trailing bush are perfect and newer varieties are quite sweet when allowed to ripen before picking. Make sure they get plenty of sun as this enhances the sugar content.

Strawberries can also be used in baskets, boxes or specially created tall pots with numerous pockets to pop in a plant. Keeping them off the ground means there is no slug problem, but watch out for birds and small children who can devour the crop long before the adults get a berry.

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A Busy Week in the Garden

A BUSY WEEK IN THE GARDEN

The variability of our British weather is so unpredictable that it is very hard to plan tasks that are weather dependant. When should I harden off plants, when do I plant my tomatoes and sow my first vegetables. At this time of year we have to watch out for that late frost. After a couple of nice warm days we get the early vegetables sown or plant those raised in the glasshouse, only to find we run into a dry spell when watering has to be resorted to. Once young seeds germinate or new plants get planted they can get a check to growth if they get too dry or we get those strong cold winds that can shrivel up tender young growth.

Although spring has been quite cool it has helped to hold back early flowering trees and shrubs now less liable to suffer a late frost. Weeds are slow but they are beginning to appear, and many lawns are getting their first cut in the second week of April, rather than the last week of March as in previous years.

However plants are wanting to grow, so there is work to be done in every part of the garden.

We did get a couple of warm days when the sun lounger came out, the winters dust got blown off, and I did manage to have my coffee break at leisure, but it is hard to relax when you know there are more than a dozen jobs all needing done.

In the greenhouse

Tomatoes. Growbags were purchased from our City Road Allotments onsite shop for my tomatoes. Both my maincrop Alicante and cherry tomato Sweet Million produced excellent plants in small pots. This year’s growbag is just a wee bit smaller than last years so I am only putting in two plants per bag rather than three. I cut out my circles and thoroughly water the compost, then leave it for at least one day to drain and warm up before I plant. I always cut slits in the bottom of each bag to allow drainage. The tomatoes are supported with polypropylene binder twine which hangs down from wire supports in the roof of the greenhouse. As the plant grows it is twisted around the twine.

It will not need any more water for a couple of weeks and no feeding till the first truss sets.

Chrysanthemums. Cuttings continue to be taken, but losses from the hard winter have killed out some varieties and weakened others. To make up my numbers I will have to take the tops out of freshly rooted cuttings and propagate these to increase stock.

Young plants of Cosmos, cabbage Golden Acre, Brussels Sprouts and my onions have now all been put out to harden off. All my geraniums were put out last week as they are usually pretty tough.

The space left will be filled with a batch of Nemesia Carnival, Petunias and Busy Lizzies which are excellent for tubs and hanging baskets.

Sweet corn plants have germinated and continue to grow strongly. They will be potted up in another couple of weeks.

Tuberous begonias are now growing slowly, but will soon need more room as these mature tubers produce big plants.

Grape Vines. All my rods which were pruned in winter are now sprouting several new growths from each spur. I will leave these alone for now as they may not all produce a fruiting bunch. Once I can see the bunches, I will remove any that are barren and thin the other down to one fruiting lateral per spur, which are spaced about nine inches apart along the rod.

The Allotment

At long last I have completed my winter digging.  I had intended to complete digging before Christmas not knowing that a two foot blanket of snow was scheduled to arrive quite early and was in no hurry to melt. That episode put back plans a wee bit.

Strawberry variety Mae is now in full flower in my low polythene tunnel, and as long as we don’t get a late frost I should be enjoying my first fruits at the end of May.

Early summer salads have been transplanted from cellular trays previously grown under glass into another polythene tunnel. I have planted lettuce, radish, spring onion, beetroot and Early Nantes carrots. They are all grown very close together, but will be spaced out as I use them.

Leeks have now been sown in a well prepared seedbed. However I still have enough leeks left from last year to crop another two weeks. They have been great value.

Broad beans are now growing strongly from a late March planting.

Kale and Swiss Chard plants left from last year continue to grow and get used as spring greens for stir frying and in soups.

Raspberry Glen Ample was wiped out by a root rot over four years, most likely some strain of Phytophthora. The dead plants were removed, topsoil replaced and mounded to assist drainage then the row was replaced with twelve pot grown Raspberry Cascade Delight. This new variety is supposed to be resistant to Raspberry root rot disease. This is now April and there is not the slightest sign of any life in any of them. Either they have been infected by the disease still around on the land, or they have not been bred resistance for all strains of phytophthora, or maybe the Scottish winter was more than they could handle. End of experiment.

I have planted up a new row, going back to Glen Ample, as it really is an excellent variety, but this time on a new part of my allotment.

Ornamental Garden

Spring flowering shrubs are now at their best with rhododendrons, azaleas, kerria, mahonia and camellias all putting on a brilliant display.

Gladioli can now be planted fairly deeply just in case there is any late frosts, but also to help support them. I will keep some back for the allotment to grow on for cut flower.

Aconites are now well past, but the seeds can be gathered and broadcast to other areas to increase the display. Each seed should flower after about three years.

Peach Peregrine flowers get hand pollinated with a sable brush every second day. Even though the flowers are late, there are very little insects around to help with the pollination.

The flowers are not very strong looking. They may have suffered in our harsh winter.

Time will tell.

Peach leaf curl disease is still affecting some new buds, even after spraying twice with Dithane at leaf fall and just before bud burst. I pick these off and destroy them.

Now, just before I find yet another job, the sun is starting to shine so I may risk a few minutes on that sun lounger.

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