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Post new topic   Reply to topic    Irish Gardeners Forum Home -> Alpines and rockery perennial plants ... Your rockery in Ireland.

Rockery Design and Construction for Ireland, a Basic Guide.

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James Kilkelly
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PostPosted: Thu Mar 29, 2007 11:27 pm    Post subject: Rockery Design and Construction for Ireland, a Basic Guide. Reply with quote

Rockery Design and Construction for Ireland, a Basic Guide.
by GPI

One of my main aims when asked to design a garden around a new house, is to soften the impact that new building has within what was once a green field site. In essence, I aim to create a situation where the opposites of hard and soft, sharp and smooth, are living in harmony within the site. A prime example of the achievement of this hard/soft harmony is to be found within the rock garden, the rocks and gravel represent the hard textures, with the soft textures being filled by the lush alpine planting.
Building a rockery is a project that many of you out there may happily undertake this coming summer, so within this article, I shall give you some insight into rockery layout, creation and planting.

Keep it natural.
A simple traditional rockery should be designed to resemble a natural rock out-crop, with plants positioned to reflect mother natures irregular seed sowing pattern. This area should use only one type of rock e.g. limestone, granite or whatever stone is local, try also to select some character-filled rock with cracks and fissures. It goes without saying that concrete blocks, bricks or pavers should not be used to make up the numbers within your alpine construction.
Unfortunately, all to often, this combination of incorrect rock selection, straight planting lines and symmetrical plant placement immediately exposes a poorly built rockery as man-made and contrived. An obvious crock of a rock(ery).

There are certain areas of your garden that may lend themselves very well to a rockery placement. For example, a bank of sloping ground that grows grass well enough, but proves un-mowable due to its steepness, this could actually be a blessing in disguise. If this situation exists within your garden, lucky you, utilise it, as rockeries often look their best when built into sloping ground or banked against a wall even.
Also, seek out sunny locations, constructing your rockery or rocky out-crop in a sun trap will benefit the growth and blooming of the particular types of alpine plants which look most at home amongst the rocks. Do not position the rockery near trees due partly to the shade factor; another problem with trees is the fact that water falling from the leaves outer edge (drip-line) onto alpine plants can quickly reduce them to soggy rotten specimens. It would also be ideal if the rockery had some shelter from harsh winds, enabling the plants to retain fresh new growth and flowers for as long as possible.

Home to the alpine.
One of the main purpose for the creation of a rockery area within your garden is to provide a backdrop and growing site for the planting of alpines. Alpines or alpine plants are usually low growing specimens, which have the uncanny ability to thrive in tough surroundings, comparable to their origins atop the Alps, Himalayas and Andes. An alpine is the common name given to any plant found on the slopes of mountains such as these, at a height above which trees fail to grow.
As water can be limited where they grow in the wild, quite a few alpines have taken on a low cushion form, while others have fleshy or hairy leaves to prevent excessive water loss, leading to the plant drying out. Most alpines can also withstand low temperatures and cold winds, but have a strong dislike of excessive rain.

Sunny mountain flowers.
Many alpines produce brightly coloured flowers because in alpine areas pollinating insects can be scarce; the strikingly bright alpine flowers are one sure way of attracting these winged pollinators from miles around. To my eye, a massed bedding display or a host of naturalised bulbs are the only equals to the colours displayed by an alpine filled rockery.
To enable brilliant alpine blooming, the industrious gardener should do his/her best to offer the plants a free draining growing position. We are aiming as best we can to recreate the situation where alpines occur in the wild, a sunny mountain slope with a gritty free draining soil.

How to create your drainage layer.
The advance creation of a drainage layer beneath the rockery will provide free drainage for the many alpine plants that require such conditions. A typical fast drainage layer beneath an alpine garden requires you to excavate down to a depth of 20 cm. Back fill the area with a 10 cm layer of rubble or large broken stone, followed by a 5 cm layer of rough gravel or chip.
The gravel used need not be the fancy decorative sort, as it will be buried out of sight, so something like the chip that is used by road workers to fill potholes will suffice. Next, cover this gravel with a layer of weed prevention fabric such "Plantex" or "Mypex" to prevent soil washing down and filling (blocking) the drainage cavities.
Finally, spread another 5 cm layer of rough gravel or chip on top, this sandwich's the fabric and fills the 20 cm excavation right to the top. This advance creation of drainage beneath the rockery is a very important step in its construction especially if your local soil is on the sticky side.

What type of soil for the rock garden?
Once the drainage layer is in place you can begin to spread and mound your soil. Soil, which will provide anchorage, food and water for the alpine planting. When creating a rockery, the type of soil you use is just as important as the plants that will eventually populate the soil. If the soil mix is not appropriate, you may get lanky stringy growth or perhaps poor growth with lessened blooming. Many novice gardeners will try to track down the nearest load of fertile soil when creating their rockery, thinking that fertile soil will benefit all types of plants, alpines included. However, you are best to use a home made alpine soil mix which is a mix of two parts coarse peat, three parts local topsoil and two parts gravel or coarse grit. The incorporated gravel, which aids drainage, need only be a rough angular limestone chip.

Mixing and mounding the soil.
If you were constructing a large rockery, I would advise you to create the alpine soil blend using a cleaned out cement mixer (you will look barmy but it beats mixing with a shovel). A 15cm (6 inches) depth of this mix is required when planting alpines; small shrubs and dwarf conifers that you may also be including within the rock garden will require at least double that depth, plus the addition of extra compost to cater to their heavier feeding roots.
Careful mounding and gradual grading of the soil mix against a solid structure such as an existing slope, boulder or even a boundary wall will go a long way towards creating that natural rocky outcrop look that alpine enthusiasts strive for. Sloping the soil away from a structure and towards the viewer allows you to appreciate the gardens colour, texture and form to its fullest, not to mention making it far easier to create layers of rock with terraces in between.

Rockery stone, safety, your back and your toes.
Before you begin to lay any rocks, a few words on safety and how to avoid future back problems....

Firstly, be careful how you lift things, don't bend at the waist, grasp the rock, and then straighten up. This puts excessive strain on your back, if you do it, years later you may regret it. Instead, bend your knees in front of the load you want to lift, and grab the weight tightly.

You should then use your legs to push upwards until you are standing. Weight is much easier on your legs than on your back. Don't forget to wear a thick pair of gloves when handling rocks, and a pair of steeltoe boots or wellies, to guard against anything dropped.

The rockery keystone.

Select rocks with cracks and fissures like the one on the right,
avoiding rounded rocks like the one on the left.

So, on to the labour intensive, but fun, laying of the stone. As mentioned previously, try to use native stone, selecting rocks with strata, cracks and fissures, whilst avoiding rounded, river or seaside washed rocks. The first and most important rock you will set is your keystone; this is usually set at the bottom of the sloped soil just to the left or right of centre, aiding an unplanned look and feel.
This keystone is the daddy and should be larger than all the others rocks on the finished rockery. Bury the bottom third to half of this keystone into the alpine planting mix with the back sloping approx 10 degrees downwards and pack the soil firmly around it.

Start as you mean to go on.
The importance of a properly installed large keystone at the base of your rockery slope can not be underestimated, as it acts as a visual anchor rock, an example for the rest of stone to follow. Observe the cracks and fissures of your laid keystone, whatever way this natural grain runs, is how all the other rocks grain must follow. This is how natural rock outcrops occur in strata, for proof look at your local rock outcrops, the Burren and the Cliffs of Moher are both examples which will surely convince you of this fact, whilst providing plenty of rocky inspiration.

An attempt to explain rock placement.
Like the keystone, all the other rocks to follow should ideally be in strata, half buried, and with a back slope of in and around 10 degrees. As well as appearing more natural, rocks erupting from below the soil are also stable to stand upon whilst you plant or weed, plus buried rocks help the plants' roots stay cool throughout a hot summer.
Don't be afraid to use different sizes of rock, keeping the similar sizes in runs of 3's, 5's or more for realism. Butt the rocks against each other in irregular arcing lines, every so often you may leave out a rock and every so often lay one rock on-top of the other.
This rock laying procedure is quite a trial and error task, which sometimes I struggle to explain to gardeners interested in the subject. Personally speaking, I often step back to survey the laid stone, walk around to gain a view from different angles, and then repositioned the rock up to ten or twenty times, before finding a form I am happy with. So, if your fussy like me, set aside a day or so for the rock laying, it may be something you may want to tinker with for quite a while.

The question of weed prevention.
Once you are satisfied with your semi-buried rocks positions, top up the rockery with your alpine soil mix, where needed, and leave to settle for a week or two, before again topping up any sunken areas. It is at this point that you must make a decision regarding weed prevention, a question of whether you require one or two layers of protection.
Doubled weed prevention would require you, at this point, to lay overlapping sheets of commercial weed barrier such as "Mypex", all over your soil areas. Set your plants through crosses cut into this fabric, and then mask the helpful but unnatural looking material with around a 5cm layer of washed gravel shingle or slate chip. The single layer option consisting of a 7cm depth of chip around your plantings, is easier to create (no fabric cutting) and almost as effective in weed suppression as the double layer.

Colour for many months.
The planting you select for your rockery will dictate whether this garden feature is a "flash in the pan" colour-wise or whether it offers multi-seasonal interest. If you are careful with your plant selections, a rockery can look attractive from early spring right through to late autumn. Simple things such as the inclusion of miniature variety bulbs, on the slopes of the rock garden will greatly add to your spring flower show.
Try the following...
The daisy-like Anemone blanda,
the bluebell (Scilla Siberica),
the snowdrop (Galanthus Nivalis),
dwarf daffodils such as Narcissus "Tete A Tete",
or rockery tulips such as Tulipa Greigii "Red Riding Hood " and Tulipa Tarda "Johann Strauss"

Dwarf grasses, conifers and shrubs.
Don't be afraid to vary the rockery planting through the addition of dwarf grasses, conifers and shrubs. Carefully selected varieties of these plants will add year round life to the rockery as well as the vital architectural element, which is often missing in many mat forming rockery perennials. For example the grass, Festuca glauca 'Elijah Blue', a tufted blue clump, 6 inches to a foot high, is ideal, as is Uncinia rubra a dense grass with pretty reddish-brown leaves and dark brown flowers from mid summer.
Of the conifers try to seek out Juniperus squamata 'Blue Star', a dwarf, light blue evergreen with a mounding habit and dense foliage or Juniperus communis "Compressa", with its narrow conical slow-growing habit and dense greyish green needles.

Don't forget why you came here.
With all the bulbs, grasses, conifers and shrubs for the rockery, you should not forget why you built this alpine style construction originally, to play host to brilliant flowering alpines. One of the alpine plants no rockery should be without is Aubrieta deltoidea "Bressingham Red" which is commonly known as rock cress.
A vital colour contributor to the garden from March until June, "Bressingham Reds" four petalled flowers cover the plants grey-green ladle shaped leaves with a deep crimson colour each year. Employ this long flowering plant to sprawl rapidly and tumble down your rockery. Trailing Aubrieta tumbling within a rock garden alongside spring bulbs such as daffodils, tulips and grape hyacinths is a great planting combination.

Tumbling Aubrieta, photo / picture / image.

Saxifraga moschata commonly known as mossy saxifrage is another vital rockery plant. This alpine grows to a height of 8 cms (3 inches), with a spread of approx 0.6 metre (2ft). The word saxifrage comes from a Latin phrase meaning, "to break rocks"; this is a very fitting phrase to illustrate the plants growing abilities.
Saxifraga moschata breaks through the natural stone within a rockery to exhibit its pink round petalled blooms above thin 4-inch tall flower stems. These flowers remain above the moss-like leaves from February until the end of April.

Saxifraga moschata, photo / picture / image.

Saponaria ocymoides commonly known as Soapwort is Ideal for growing on a high points of your rockery as it tumbles delightfully downwards from a height. It is absolutely covered in pink flowers during the summer.

Rockery Soapwort , photo / picture / image.

Helianthemum commonly known as rock rose is a brilliant rockery plant, flowering over a extended period of the summer. I have shown a yellow variety below, but it is also available in white, orange, red, and pink flowering varieties.

The yellow Helianthemum "Ben Fhada", photo / picture / image.

Creeping Thyme is another plant to look out for as it is very easy to grow. Apart
from its attractive flowers, it will also produce a lovely fragrance as it carpets your rockery. Plant it in an area where you will brush past it to release the aroma.

For lovely fragrance plant creeping thyme Thymus serpyllum, photo / picture / image.

Planting two or three of the same alpine plant closely grouped together will add great impact to your planting scheme. Happy planting!

Any queries or comments on this Rockery Design and Construction article, please post below.

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Last edited by James Kilkelly on Thu Apr 26, 2007 6:30 pm; edited 1 time in total
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