The Lie of the Land
Knowing the orientation of your plot is crucial
This is for those of you currently at the observation and analysis stage of your Permaculture design process: there’s some really good advice to be found on the Telegraph website gardening section these days.
In this piece on understanding the lie of your plot Bunny Guinness writes:
“It's not just bees that love a sheltered, sunny garden: many plants perform better, too. In older walled gardens, where they had to maximise production for survival, gardeners frequently used to choose or make productive land slope south, to receive the maximum amount of the sun's rays (ideally the rays should fall at right angles to the soil for as long as possible). They chose well-drained soil, which heats up faster, and soil protected from fog, frosts and damp. The walls might well have been screened by a belt of trees for shelter. Dampness affects the temperature quite dramatically, because water removes heat from the surroundings as it evaporates. Even the colour of the soil affects the speed at which it heats up, with darker soils absorbing more heat than lighter types.
Frost Pockets and Hot Spots
Cold pockets are obviously worth avoiding when you want early vegetables and fruit. Sometimes you can remove a frost pocket by taking out the hedge or the obstruction that is stopping the cold air from rolling on down the slope. Fruit growers in orchards would mist early-flowering crops when frost threatened, as water forms an insulating layer over the precious flower buds. It is also thought that when ice forms a protective case around a flowering bud it can protect the buds so the cells do not freeze. When you see signs of an air frost (tall stalks covered with a filigree of white) you know it is cold - far colder than when you just see your grass frosted (ground frost). For this reason, temperatures are recorded at a height of 1.5 metres, because the closer you get to the ground the colder it is, as hot air rises. If you love sun traps and want maximum temperatures, maximise south-facing walls, hard paving and gravel - and avoid greenery.The former will encourage absorption of the sun's rays and keep radiating them through the evening and night. You will probably need to add a vine-covered pergola to cool you down!
The welcome cooling effect of a body of water has been exploited in warm climates for centuries. The evaporation and release of negative ions into the air cools and calms you. The thermal inertia of water - it takes a long time to heat up and cool down - means it is still radiating warmth after the rest of the garden has cooled. Polytunnel expert Joyce Russell recommends putting buckets of water into cold greenhouses and polytunnels in order to help nudge the temperature gauge up that extra all-important degree or so at night.
The prime way to change the micro-climate is by covering an area. Joyce recorded minimum night temperatures in her polytunnel 8C higher than outside it. She cannily left the snow on top of the tunnel (great insulation) but removed it from the south-facing side to steal the sun's heat. Generally though, at 3am the temperature under glass or polythene, inside or out, will be similar. You get earlier crops inside because the daily thermal gain is higher, and the long-wave radiation emitted from the ground at night is retained to an extent by the cover, the amount varying with the material (glass retains more than polythene). Covering veg beds before sowing early spring veg is effective, and experiments at Sparsholt College, Hampshire, showed that clear polythene heated the soil 2C more than black polythene or any other cover tried.
I thought this was a major factor in cooling, but Peter Gibbs put me right. The primary way wind cools is by evaporation, and wind will never cool below the ambient temperature. Once you've designed your sun trap for your sun lounger, you need to make sure that the wind won't cool it down. Most gardeners agree that plants usually grow better in sheltered conditions, and hedges and shelter belts are my first consideration when developing a windy site. If you want a warming job, now is a prime time to get those young plants in!
How to manipulate a garden's temperature
Analyse the lie of your garden, its compass orientation and the fauna that is around it to get the best out of your plants. Taking note of the direction of the sun travelling over your garden is important Whenever I speak to weather-obsessed gardeners, I find out fascinating new information. Our foremost meteorological gardener, Peter Gibbs, recently did some studies in the Devon garden of Carol Klein, the Gardener's World presenter. The results surprised him. Carol's garden is not large, but in August Peter recorded 25C/77F in a hot spot, but only 18C/64F in a damp, shady spot - the sort of difference you might find between St Tropez and Southport. The amount of rain received also varied hugely, with 50 per cent less on the leeward side than the windward side. Knowing what affects the micro-climate in your garden really gives you a head start. Most gardeners want light and shade, dry and damp, sheltered and exposed areas in which to grow different plants and create contrasting spaces. But with a few tricks, you can manipulate your garden's temperature to get the best results.”
from Bunny Guiness's article on:
(Related articles are also listed – including:
Tips for plant hunters 27 Jan 2011 Gardening week ahead: How to renovate climber and rambler roses 29 Jan 2011 Roses in history and culture 27 Jan 2011 10 new and improved fruit, veg and flowers 27 Jan 2011 Gardeners who got caught out by the bad winter 25 Jan 2011 How to extend your growing season with a polytunnel 21 Jan 2011)