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Knowing the relief of your garden is as important as knowing the texture of your soil. Water will behave differently in the garden depending on the slope of the land !
Find out the different levels
Land is never really flat. If your garden is on a slope this is quickly realised. However, in most cases, the difference in levels is not obvious to the eye. You may think that the garden is flat but really, it is on a slight slope. The best tools for finding out these different levels are those used by surveyors... but for garden use, they are not worth the investment! A more simple approach is to plant a post in the ground that is exactly vertical using a spirit level or plumb line. Then with a setsquare, you line it up with a point at the end of the garden: if the land is perfectly flat, you will need to lie on your stomach to line up the mark on the setsquare with the end of the garden !
Effects of a slope
Where there is a steep slope then it does not take a genius to understand that the rainwater will run off without going into the soil. If it is bare soil then this will lead to the creation of small streams of water and gulleys in the earth. This causes the ground to erode and crack leading to other problems.
If the slope is more gentle, it will lead to the creation of damper areas, which will dry out slower in the summer. This is known as damp soil. Damp soil is not an area with cold soil but an area that never dries out !
Beat the slope
First of all try and benefit from the slope by planting plants in the damp areas that demand more water, and those that are more drought resistant in the higher areas. This will not always be enough. Where there is the risk of erosion, it would be wise to install something to retain the soil or choose your plants carefully.
Landscape the garden accordingly; this includes the creation of retaining walls, terraces and stone walls giving a terraced effect. This will involve a considerable amount of work to create the terraces but is the only real long-term solution: in the old days, the stones were carried up on the backs of men or donkeys! The terracing will have a very pleasing effect and will create a viewing point at each level. The flat land between the walls can be used for growing. In this way, water will take time to be absorbed into the ground and benefit the plants. It will also be more equally dispersed over the land.
The other solution involves playing around with the plants used, favouring trees that retain the soil. In bygone days they used to plant « False Acacia » trees along the side of railway lines to stabilise the embankments. However, like the Ailanthus tree the False Acacia has become something of a nuisance so it is better to look at some other plants. It would be better to use plants such as the Sea Buckthorn, decorative Dogwoods or the Bladder Senna (Colutea). You could also during the autumn plant some willow saplings fixing them in place like posts. They will only grow if the soil is damp and humid.
If you are faced with a dry embankment that is threatening to give way, it is best to build a supporting wall as these retaining plants will not grow quickly enough to hold the soil in place ! - Photos (1)
Rain run off and the slope
Find out the different levels
Author: Jean-Michel Groult
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