The Mountain Garden
Height above sea level is not the sole criterion of a mountain garden. A windswept, craggy hillside in Scotland, some 1600 ft (500 m) above sea level might qualify, but a warm and fertile plateau in Ecuador, situated at many times this altitude, would not.
A true mountain garden has steep slopes that are exposed to severe winds and thin soils prone to erosion and alternate waterlogging and drought.
Apart from stunning views, its advantages include a distinctive local flora, clean air, and some dramatic natural features.
Steep slopes have secondary effects: rapid erosion in heavy rain and exaggerated patterns of light and shade. The orientation of the slope with respect to the sun has a profound influence on a garden at higher latitudes: a sunward slope brings many natural advantages, while a sunless slope will limit the possibilities of most sites.
Trees, shrubs, and herbs
Mountain soils are often poor because nutrients are scarce or because poor drainage causes undue acidity. On heathland, the light soil can be improved by leguminous and cover crops, and by adding organic matter. On acidic moorland, the soil is peaty and organic matter is plentiful, but plants find the nutrients harder to extract because of the particularly low pH.
Here, you can grow various ericaceous, lowshrub, berry crops, such as blueberry, huckleberry, whortleberry, cranberry, cowberry, bilberry, crowberry, elderberry, and salal. You can also cultivate a range of acid-loving crops, such as rhubarb and strawberry.
In mountainous areas of the humid tropics, erosion can quickly deplete the soil on cultivated land. Terracing the hillsides slows the downflow of water, allowing eroded soil froth higher up to be trapped and saved in the lower terraces.
In the absence of terraces, it is essential to maintain tree cover in order to minimize erosion. If the ground slopes steeply toward the sun, you can locate trees almost anywhere without causing undue shade.
The direction of the most problematic winds can be the critical factor in determining where to plant them. If the ground slopes steeply away from the sun in mid and high latitides, any trees on the sunward side will shade both garden and house; tall trees are most suitable at the bottom or sides of the garden; wind shelter on the sunward side must be provided by fences and hedges.
Trees and shrubs play an important role in soil stabilization and creation. Without compromising your other goals in the garden, keep existing trees and plant others if necessary. The minimalist mountain gardener relies entirely on plants that can tolerate the conditions.
Some produce edible fruits—juniper, mulberry, olive, carob, almond, blackthorn, the Vacciniums, myrtles, bayberry, and gooseberry; others are woody aromatic herbs, such as thyme, sage, rosemary, lavender, and marjoram.
Water management
The relation of the slope to the house is of daily importance, not only because you have to go up and down the garden, but also because you have to manage the water supply. Mains water from a pressurized supply will reach all parts of the garden; but in the absence of such a system, or if you wish to use grey water and runoff, it's obviously easier to run the water downhill!
Surplus runoff from the main body of the garden, collected via diversion drains in a storage pond, gives the greatest yield at the bottom of the slope. But if you need the water for irrigation, site the pond near the middle of the slope, with plants that need watering below it.
Set up another pond at the bottom for use in emergencies. Similar logic applies to the movement of other bulky materials, such as compost, much of which arises within the garden itself and is concentrated on intensive crops.
Steep slopes often have thin soils simply because the soil falls, or is washed off the underlying rock. Rain gathers into rivulets and streams, washing the soil into the valley or plain below. To avoid losing soil, slow the water and disperse its energy; the simplest way is to break up the flow with rocks and cascades.
An alternative approach (you would probably need to do both in reality) involves creating what are in effect miniature valley bottoms. These intercept the flow of eroded soil and nutrients, and slow down the water runoff. To this end, all permanent landform features are constructed across rather than down the slope. Such features include ditches, swales, banks, berms, terraces, and retaining structures.
At high altitudes with a short growinq season, vegetable gardens can still flourish, as in this example, from the Swiss Alps (below ***). Although the winters are severe, the heavy snow cover protects many perennial crops from fatal damage. The so-called "alpine" plants thrive on the regime of sharp dry printers, well-drained soil, and a resolute thaw. They do not do so well in the erratic weather of milder oceanic climates.
The value of terracing
At its simplest, terracing cuts into the upslope and spreads the excavated material below the cut. This results in a level area at the expense of even steeper slopes above and below—these need to be supported or retained in some way. It is traditional, obvious, and appropriate to use the features and natural rock of the mountain for the retaining walls of terraces.
The effect of terracing is to increase the depth of soil, and trap water and nutrients flowing from above. You can grow the more demanding crops in the richer soil of the terraces. Always look for ways to solve several problems at once: steep slopes can, for example, offer trees shade and shelter without root competition, together with easier harvesting of fruit.
Access to very steep terraces can be a problem. Steps are best for retaining soil; they use the least space, but present a serious obstacle to wheelbarrows. A good pattern is a slow zigzag of gently sloping terraces, using the retaining walls as pathways. If possible, deliver and store materials at the top of a slope, so they can be carried downwards.
