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Stabilizing Mediterranean Gardens on Slopes

When my garden landscape company was in business a few years ago in the Mediterranean I had to undergo a very difficult garden project set on one of the steepest sloped Mediterranean gardens I have ever seen. The gradient of the slope was so steep that the staff building the garden with me had to use ropes to climb up and down in order to carry the materials. The owners had just moved into their new home and they were very disappointed that they could not use the garden, as a pleasant aesthetic garden to walk around. For instance, to walk, admire the views and sit outside in the warm summer evenings. And because the house was situated on a steep slope they had good views all around to the valleys below, great for sitting and admiring the views but at the moment the garden had absolutely no aesthetic attraction – no plants, just a lot of unhealthy and dying old trees and also bad quality soil. And to make it worse the gradient of the garden was so steep that it made it almost impossible to walk on – so this was a challenge – how was I going to make it into a garden fit for plants to grow happily and how was I going to make it a garden inviting for people to walk around? It was a tall order, however, the solution came to me very simply. We need to make an old stepping-stone path around the garden and in between the stones we plant low growing spreading plants that will bind the soil and hold the rocks and soil in place. In other words we use plants to stabilize the soil. It could be done but it was going to be a lot of hard work. But I like challenges – and so I set about talking to the owner about my design ideas.

The owner liked my thoughts and asked us to set about with the project. However, before we began, preparation was needed, the garden had to be cleared. It was full of old, dying trees and old bushes and weeds. So we set to work. The first major step was to remove and kill all the old unhealthy trees by cutting the trees down to their stumps. The tree stumps were kept to hold the soil stable. It didn’t matter if the stumps were left because we could disguise them with plants and rocks around them. As long as the stumps were not allowed to grow back again of course. The second task was in three stages, first we needed to stabilize the soil so that in the winter months the rain would not erode and wash the soil down the slope. It would have been possible to stabilize the soil by building a large retaining wall with terraces and steps down to each terrace. However, because the garden was so big, this would have cost the owner thousands. It was a nice idea but not financially practical and in my eyes, this would not have been an interesting garden. The answer was to build this lovely dry-stone stepping stone path meandering through the garden, creating a natural effect and at the same time eliminating the chance of soil erosion. And for extra stability to prevent more soil erosion larger boulder rocks were placed throughout the garden so that when the plants were introduced the plants would then hold the soil, again, to stop erosion. Imagine carrying and placing 2 x 26 tonne lorries of boulder rocks and stepping stones down a slope and the only foothold the staff had was hanging onto a rope for security!

The final task was planting. The soil around the house and other houses around this vicinity were renowned for very poor chalky soils, therefore all the plants had to be sub-planted with at least 2 foot of really good quality red top soil and compost – again each plant was planted with the staff going up and down the slope on ropes. But the major importance, and the one reason this garden would be a success or failure was the types of plants that we used.

Because of the steepness of the slopes the plants needed to be particular plants that would stabilise the soil, soil-binding and spreading species. We chose to use a lot of evergreen dwarf spreading conifers, such as, Juniperus horizontalis, Thuju aurea nana, Rosmarinus corsicus ‘Prostratus’ or Rosmarinus officinalis lavandulaceus and Pinus Mugo nana. We also chose to use dwarf grasses, that would spread but give a mixture of different colours, especially for the winter months, such as Festuca glauca (Blue/grey grass), Ophiopogon (lush green grass), Carex (variegated yellow grass) and Bambusa nana (compact lush green mini bamboo). Because all of the above are classed as evergreen plants giving permanent green throughout the winter and summer, it was also necessary to include some spreading, compact plants that would give colour, especially throughout the summer and winter months such as; Margarita rose (pink button flowers), Mounding Santolina’s (yellow button flowers), Osteospermum (lovely purple and white spreading flowers), spreading bush bougainvilleas, giving a dominant selection of either red flowers or pink flowers, the bush variety is not very common but if you find it, it can be ideal to use as a colourful-spreading plant, and Felicia, with its lush green mound and lovely purple daisy-type flowers, and last but not least, a few different varieties of Lavender stoechas, the french lavender to give long-lasting purple & blue flowers and Tulbaghia violacea, also known as society garlic or pink agapanthus, is a species of flowering plant in the onion family Alliaceae and has compact perennial grass-like leaves with heads of dense purple flowers throughout the summer and winter months.

All these plants are ideal for slopes, but do remember, all these flowering plants were put onto an automatic irrigation system and so they were watered for 3 minutes every day. Obviously this will keep all the plants healthy and happy but with full sun in the Mediterranean it means that the flowering plants will grow very rapidly and must be cut back regularly over the summer months, down to the last green shoots. All of the flowering plants will be mature in about six months and will look stunning once they have spread over the big boulder rocks and blending with the lovely meandering stepping-stone path!!

Need some plant advice? For more details, pest and disease advice or plant ideas for your own individual garden conditions – please contact me on the home page or write to me at the plant diagnostic service contact home page

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