changes of level

©2003 mark laurence

design note no. 2073

subject:	Defining changes of level on a slope
problem:	Slopes are difficult to live with if they are too steep.

A garden without any changes of level is intrinsically boring; in such a garden, one might expend considerable effort putting in place devices to change the levels and give emphasis to vertical elements. Yet natural contours, if too steep, can become problems in their own right.

problem:

Gardens built on sloping ground give rise to significant challenges; first is the matter of aspect. A south facing garden will burn up in hot summer weather, whilst a north facing one, particularly if wooded, may never experience direct contact with the sun at all. Such matters cannot be changed, and must therefore be worked with - they will dictate to a greater extent the type of garden created there.

Other problems that may occur involve physical movement and rest. Steep slopes are difficult to walk up or down and treacherous when wet. You cannot stop and rest - they are places of movement only - still-points cannot occur there.

Children, the elderly or infirm will have special difficulties dealing with slopes - but so might a mother carrying a baby or anybody with a drinks tray! Cutting grass on slopes can be dangerous too.

solution:

Terracing is the time-honoured method of dealing with slopes and for obvious reasons - it is the only method of creating level stretches of land on a slope. These are achieved by a method called cut-and-fill. Cut partly into the slope, build partly out. Minimal moving of soil and rocks is involved. But is it the right solution in a garden?

We have to realise that there are two distinct types of use for terracing; first where a large wall is used to build up the level behind it, creating two areas of more or less level ground and second, where a series of terraced ledges are created all the way up a slope. Both have their uses, but to my mind, it is the latter use that gives most excitement - the former usually seeks to level out the ground and create essentially flat spaces. Whilst this may be necessary for a tennis court, in general gardening terms I feel that this type of levelling tries to deny the essence of the site.

Where a slope is turned into a series of mini-levels, however, it becomes a series of unique micro-climes, each to be given its own character and usage. Each terrace then becomes something different and suddenly we have a stage setting for rich experience.

Paths can wind up through terraces in a series of zigzags, water can tumble down from level to level (don't forget that water-courses have to be built in a series of level stages and falls). Walls can trap evening warmth, pergolas give shade - the scope of terraces is endless. Essentially, you become immersed in a series of three dimensional spaces, which build through many layers to form a sense of place.

From a practical point of view, level, or near-level planting beds are to be preferred to steep slopes. Soil and mulches wash away down slopes during heavy rain, leaching nutrients. And because the rain runs down the slope, it does not soak into the soil as it should, leaving plants susceptible to drought. On a north facing slope, terracing can maximise the limited light and increase slope temperatures - perhaps those vital few degrees that would make all the difference to good plant growth.

Cut-and-fill terracing is solid, permanent and expensive to construct. A less permanent but more economical solution can be considered using decking to form level areas, along with timber raised beds.

You may wish to look at the the following related design note:
3074: terracing with decks and
construction notes section, which deals with methods of building retaining walls