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Garden of the Season - April 2012

Creating a New Raised Bed Rock Garden

Introduction

I have held a passionate interest in alpine plants and rock gardening since my later teenage years in the mid 1980’s. I recall being given a 1970’s book on rock and water gardening by a former girlfriend’s father, who himself was a keen gardener with a love of alpine plants. I read the book from cover to cover several times and in particular was fascinated by the photos of alpines in a garden situation. I have grown alpines or ‘rock garden’ plants ever since. I have also made a career from horticulture and I now have my own business ‘Dragonfly Designs’, as a specialist gardener and landscape designer. I try to include alpine plants or easy-going rock garden plants in many of my designs because they are such versatile, varied and fascinating plants, particularly for modern small gardens.

This leads me on nicely to a recent and ambitious project in the family garden. Having relocated from North Wales to North Kent in summer 2011, I was asked to create a large rock garden at the family home. Located outside the village of Longfield, in north-west Kent, the garden is in an area of low annual rainfall with less than 750mm per annum on average. The underlying rock is chalk and the soil is stony, very well drained and prone to drying out. At the front of the property there is long L-shaped raised bed, approximately 23 metres in length and 2 to 2.5 metres in width. The bed faces south for the majority of its length and then curves around to face west. The eastern end of the raised bed receives some shade from early morning sunshine due to a large Sycamore tree which is located several metres away.

Before redevelopment the bed was planted up with nine Columnar Junipers and a number of prostrate spreading conifer varieties. All of these had outgrown their allotted space and the soil was so dry and impoverished that only a few hardy geraniums and a scattering of bulbs were holding on for dear life! In amongst all the conifers and struggling plants were a large number of Ragstone (Kentish Limestone) rocks of varying sizes.

With a ready-made brick retaining wall, an open exposure and a supply of rock to be reused, the raised bed was ideal for creating a rock garden. The bed would also act as a demonstration of my landscaping skills and (hopefully!) an excellent advert for my burgeoning business.

(Photo 1: The raised bed full of conifers before redevelopment took place.)

Construction

Work began on this considerable project in mid-July 2011. The first job was to remove the ragstone rocks and also any plants and bulbs worth salvaging. The next part of the project was handed over to professional tree surgeons, which came in to remove one medium sized sycamore directly opposite the raised bed and casting considerable shade. They also cut down the conifers in the raised bed and removed the brash. The effect on the house was instant with a great deal more light now reaching the house and an open aspect at the front. The bed looked very bare apart from the sad looking conifer stumps; however I was confident of creating an attractive raised bed rock garden which as it matured would provide many years of colour and interest.

A great deal of hard work lay ahead over many weeks. The job of removing all of the conifer stumps and roots was beyond digging by hand and therefore another contractor was brought in to dig out the stumps using a JCB digger. The contactor also removed many tonnes of the original tired and root filled soil. The replacement of the soil was vital to the success of this project; however this was a huge undertaking and amounted to three large skips being filled with soil and taken away for recycling.

(Photo 2: The JCB in action clearing the old tired soil, conifer stumps and roots.)

Unfortunately the conifer roots had penetrated underneath the very old wall at the back of the raised bed and severely weakened it. The decision was made to demolish the wall and to build a much lower retaining wall topped with York stone copings so that the plants would be clearly visible from the house. All the bricks from the old wall were broken up and used as an extra layer of drainage material underneath the soil mix. The soil mix was obtained from a local company as a bulk delivery and amounted to twenty tonnes of a compost, topsoil and sharp sand mix. In addition to this seven tonnes of the local limestone (rag stone) chippings were also delivered in bulk for topdressing the rock garden and also for mixing into the soil mixture to further sharpen the drainage as required.

Before the soil mixture was moved into the raised bed from where it had been tipped on the driveway, an irrigation system was laid consisting of a number of hoses blocked at the lowest end and pierced all along the length with a quick release connector on the end above soil level. These hoses would provide moisture deep down in the raised bed during times of drought and would be fed by water collected in rainwater butts at the side of the house (700 litres in total!)

(Photo 3: Twenty tonnes of soil mixture looms on the driveway! The irrigation hoses would be covered with hessian to prevent soil mixture from washing down into the drainage layer below.)

Once the arduous task of barrowing nearly twenty tonnes of soil mixture from the driveway to the raised bed was completed, an amount of the limestone chippings (approximately two tonnes) were mixed in using a hired petrol rotary soil mixer . An old cement mixer was also utilised to painstakingly create the correct mixture!

A point had now been reached after many weeks of effort, where work could now begin on constructing the rock work. Terraces and crevices were created to give cool root runs for the plants on a predominately south-facing planting area. The bed would receive sun for most of the day and alpines requiring some respite from the hot summer sunshine would be tucked into the shade of a rock crevice or on the north facing side of a prominent rock. Constructing the rockwork was one of the most enjoyable parts of the project and I was satisfied with the final result, even though a few more very large rocks wouldn’t have gone amiss.

(Photo 4: Constructed planting terraces and crevices from the ragstone rocks rescued from the previous planting scheme.)

Creating the rock work took three full days and the rock garden construction was completed with the application of around four tonnes of 6mm to 10mm limestone chippings, quite a task in itself!

The construction stage of the project had now been completed. Work had begun in mid July and at the beginning of September the bed was ready for planting out.

Planting

At the beginning of September I had the exciting prospect of planting out the huge completed raised bed rock garden, with around 60 squares metres to cover. This planting period also coincided with the warmest spell of weather of the whole summer in the south east, with the mercury nudging 29 degrees centigrade on several days! Initially groups of dwarf bulbs were planted and marked out and these totalled over 600 in number. Varieties of Species Crocus, Iris, Narcissus, Scilla and Tulips were planted across the garden along with autumn flowering Crocus species, Sternbergia, Chionodoxa and Puschkinia. With the bulbs planted, the next stage was choosing how to plant out around two hundred alpine plants. Many of the plants had been sourced from the excellent Aberconwy Nursery in North Wales prior to our move south. I also had many plants in my collection, itching to be released from their pots and allowed to roam with freedom in a raised bed.

The idea for the raised bed was to have plants included for impact and interest on a year-round basis. Due to the scale of the bed and the mainly south facing aspect, a significant number of easy-going alpines were included into the scheme. Plants such as Aubrietia cultivars, Campanula species, Thymus species and some of the easy Phlox species were all included to create cascades of foliage and colour over the rocks and front wall of the bed. That is not to say that the bed is totally devoted to easy alpines and many unusual and choice plants have been added to the bed, tucked away in rock crevices in many cases. Further plants will be raised from seed from the AGS seed exchange scheme and added over time. Copious amounts of watering and wetting of the gravel to raise the humidity levels helped to carry the newly planted alpines through the late summer heat wave and despite appearing fairly sparsely planted, I knew that during 2012 the plants would really settle down and put on lots of growth.

(Photo 5: A section of the raised bed around two months after initial planting, showing plenty of room for new additions!)

Spring Bulbs

After a mild and fairly dry winter in the south east (apart from a cold snap in early February), the late-winter/early spring bulbs, began to light up the raised bed in mid February. A selection of photos taken from the bulbs first appearing to how they look in mid-March, gives an idea of how this newly planted garden is progressing. As the plants and raised bed develops through 2012, I will add further updates to the website. It will be very exciting to see how this raised bed rock garden develops over time.

(Photo 6: The first bulbs to emerge after the early February cold snap, Iris danfordiae.)

(Photo 7: A drift of Crocus chrysanthus 'Cream Beauty'.)

(Photo 8: Iris histrioides 'George' backlit by the late winter sunshine.)

(Photo 9: Iris reticulata 'Pixie', one of my favourite cultivars of the Reticulate Iris group.)

(Photo 10: Pale blue Iris reticulata 'Cantab' contrasts with Iris reticulata and Iris 'Katherine Hodgkin' in the background.)

(Photo 11: Saxifraga 'Mona Lisa' with beautiful primrose yellow flowers, happy on the shadier side of a rock.)

(Photo 12: Tulipa kaufmanniana 'Stresa', possibly a touch vibrant for some; however I feel a drift of these works well on a raised bed of such huge scale.)

If you would like to see further images of the raised bed rock garden and other garden projects utilizing alpines, then please visit the ‘portfolio’ section of my website:-

Dragonfly Designs website

If you would like to see the latest images then click the Facebook link on my website which will take you directly to my Dragonfly Designs Facebook page. 

Paul Lewis