Harnessing Natural Energies

The energy flows outside your house and garden are not always to your benefit; sometimes you need to encourage them; sometimes divert them; sometimes you need to do both.

Energy patterns differ in different parts of the world, and even from one garden to another in the same region. You need to know your own, so during your first year find out what you can about the energy patterns around your garden.

The principle energy sources are the sun and the wind; you need to be aware of their effects on plant growth, temperature, and humidity. Monitor these effects through daily and seasonal cycles, and discover the times when they are too powerful, just right, or too weak.

Light and shade

A garden analysis will reveal a pattern of light and shade that follows a daily and a yearly cycle. The daily cycle will change as the year progresses. Imposed on these two inflexible cycles is the weather, which is predictable in some areas, much less so in others.

The cyclical patterns of light and shade make a great difference to your gardening strategy because light is not only a source of energy for plants but; it is also a source of heat. Light and heat tend to go together.

Plants, particularly crop plants, are like people: in hot, sunny climates the surfeit of light and heat encourages them to seek a certain amount of shade; cool, cloudy climates make them crave light and warmth.

In those climates that alternate sunny–hot–dry with weak sun–cold, there is the problem of requiring shade in one part of the year and avoiding it in the other.

Maximising light

If your garden lacks light (especially if it is in a high latitude), choose strategies and plants that work in shady conditions; you may have to abandon plans to grow highly productive edibles, but you can still choose from a wide range of useful crops. The range is much wider at low latitudes.

• Identify the sunniest parts of the garden and concentrate light-demanding species there. In high latitudes you need to identify parts that are sunniest in the growing season.

• Amplify light in sunny spots with light-painted vertical surfaces. This is particularly effective in sun-reflecting corners.

• Remove elements that cast shade, such as walls, fences, garden buildings, and trees. Be careful because such elements often provide shelter from the winds, privacy, support for plants, and "structure" to the garden. Removing established trees can be a particularly difficult decision

• Design the garden plantings with a profile that slopes toward the sun, with tall trees at the back, graduating to the most light-demanding plants at the front.

• Tilt productive beds toward the sun. This is particularly useful in high latitudes or where the ground slopes away from the sun side. The effect of a 5-degree change of slope can be equivalent to flat ground 300 miles (483 km) nearer the equator. The disadvantage of this is that when productive beds are sloped toward the sun; they create an area that suffers a great deal of shade. This problem is minimized by making the back slope very steep and, at a later date, a place for shade-tolerant or taller crops. Probably the best solution is to build a permanent retaining fence or wall, with a path behind it. The ultimate development of this is a series of asymmetrical raised beds oriented east-west and sloping toward the sun.

• Plant annual crops in cast-west rows with small varieties on the sunward side and successions running toward the sun, so that older and larger plants do not shade younger ones.

Designing for permanent shade

Some low-latitude climates are characterized by perpetual sunlight with air and ground temperatures that are usually much too hot. Year-round shade therefore becomes a premium. Some plants demand shade anyway; others, though unaffected by strong sunlight, still suffer from overheating and excessive transpiration.

People, too, need shade and plants not only provide a cool sanctuary in the garden but they also shade the house.Priority should be given to east- and west-facing parts of the garden and house, for here the sun is low in the morning and late afternoon.

After the intense heat of the day, shading from the western sunshine is particularly important. When the sun is overhead, the only effective shading comes from a canopy of leaves and, for this reason evergreens form a vital part of any plans for permanent shade in your garden.

They can be supplemented with evergreen vines trained over open frameworks. I n general, a permanently sunny climate offers more possibilities than a dull one: you can always reduce high sunlight levels, but you cannot tease more light from the sky than it is willing to give.

Seasonal light control

In mid to high latitudes, where you have the additional challenge of designing for seasonal light variations, your best strategy is flexibility and the best plants to work with are deciduous trees and vines. They allow sunlight through in the winter but provide shade in the summer. This strategy needs care because the winter canopy of a deciduous tree can cut out a significant fraction of the light passing through it. You need to weigh up the respective benefits between winter and summer, and decide which seasonal light suits your garden best.

Deciduous or annual vines can be trained to cover a trellis or a pergola, thereby making a shadehouse for appropriate crops, which doubles as a pleasant arbour. Furthermore, annuals do not cast winter shade! The winters of many continental climates are so severe that nothing happens in the open garden anyway and you don't need to worry about the deep winter sun. It's the spring you must design for, to give plants an early start and to maximize the growing season. Here, the sloped-bed system is beneficial.

As far as cropping patterns are concerned, some of the recommendations for dull climates can be simply reversed, with earlier crops on the sunward side shading those behind them. Many crops which need full sun to get them going in the spring will suffer under the full heat of summer sun. This suggests the need for a pattern of shade-requiring inter crops (see ***), such as lettuce sown between rows of maize.

The importance of heat

Although sunlight and heat are intimately connected in energy terms, you can often distinguish one from the other in the responses of your garden plants. I n mid to high latitudes, light in springtime increases rapidly. but the air and soil remain cool. The plants have plenty of light, but they are just not warm enough for optimum growth, especially the roots. In the autumn, the opposite is true: both the air and soil are warm but levels of sunlight are declining as the days grow shorter and the sun does not climb so high in the sky. In very sunny conditions, plants rarely suffer from too much light, just heat stress resulting from an excess of transpiration.

The amount of heat which plants need and to which they are susceptible is also determined by many other factors, including air temperature and humidity, wind, the type of soil, and ground moisture. This is the orchestra that you need to conduct to get the ;maximum benefit. Not enough heat prevents plants from growing properly while too much heat may cause plants to dry out.

Not enough heat

The temperate gardener's critical time is spring, because what happens then determines growth for much of the year. Lack of heat prevents germination and slows the activity of the bacteria that make soil nutrients available to the plants. There are ways to get round this, thus:
• pregerminating the seeds
• bringing on the seedlings in the greenhouse
• warming the ground before sowing or planting
• providing shelter for young plants
• designing the productive area of the garden for early warmth.

Pregermination

Each species and variety has its own range of optimum conditions for seed germination. It is easier to meet these conditions in the kitchen or the conservatory than in the ground outside. Most seeds need a combination of warmth and moisture, but some need special treatment—nicking the seed coats, freezing, or even boiling water.

Bringing on the seedlings

Rather than plant out germinated seeds, bring on the seedlings and let them become established. You can do this by allowing seeds to germinate in pots or trays of soil or potting media in the house, but as soon as the seed leaves are through give them light. So you must have, in descending order of usefulness, a heated greenhouse or conservatory, an unheated conservatory, a cold greenhouse, and a cold frame.

A fully heated greenhouse is a great luxury but it is inefficient: most of the heat is wasted. The most natural way to provide heat for germination and seedlings is to make a hotbed.

The benefit of sowing and bringing on the seedlings indoors before planting out is that your plants are guaranteed a good start. It also protects them from freak frosts, pests, and the fungal diseases that affect weak and stressed plants. They will be bigger and "farther on" than those sown at the same time outside. On the other hand, plants that are sown direct, if they do make it, are often stronger. It is a minor drawback of growing plants indoors that you must acclimatise them or harden them off (see ***) before planting them out.

Warming the ground for sowing

Apart from germinating seeds,. increases in temperature stimulate the activity of both roots and soil micro-organisms—especially the bacteria and fungi that are so vital in making nutrients available to plants. If the soil is too cold, roots cannot operate effectively, even if the air is warn. This is one reason for bringing on plants under cover.

Another difficulty with spring sowing is that there is a chance of a freak late frost. This problem is traditionally overcome by cloching (see ***). This involves covering the plants with mini-greenhouses that will trap sunlight, retain heat, and keep out the cold wind. A cloche (from the French word meaning bell) was originally an open-bottomed bell jar or else a square frame with a handle on top. Cloching can be organized on a plant-by-plant basis, in rows, or even in whole beds.

Solar greenhouses

All greenhouses, whether of glass or plastic, trap sunlight for warmth. The light passes through the transparent skin, and is partially transformed into heat when it strikes the solid interior. This heat is re-radiated at a different wavelength, but can't get out again because glass and (to a lesser extent) plastics are opaque to heat radiation. In this sense all greenhouses are "solar".

In mid to high latitudes and altitudes, however, ordinary greenhouses lose their heat quickly when there is no sun. .A solar greenhouse has a number of features to prevent this:

• Only the sunward size is glazed; as the sun is low in winter, a glazed polewardside won't lose more heat than it gains.
• The poleward side is highly insulated and faced with internal reflecting surfaces; these amplify light on to the plants and reduce heat losses.
• A large thermal mass stores heat during the night and sunless spells.
• Double-glazing and retractable insulating shutters (at night) reduce heat loss through.

In favourable circumstances, solar greenhouses can keep a good internal temperature throughout the winter with no hear source except the sun. They work best in climates with a reasonable incidence of winter sunshine; they arc less effective in oceanic climates, where the winters are generally overcast.

You can solve the problems of cold or wet ground by covering the soil with an impervious mulch (see ***) for at least a month before you wish to sow.