Whether or not we as a species are responsible for any significant change to our climate for sure we as individuals can do little to correct it and but slowly. As gardeners however we can improve the micro-climate for our plants quite significantly. Here in the colder climates of Northern Europe micro-climate improvement is almost invariably striving to give our plants more shelter, warmth and light. In sunnier climes the converse is often more important and there many of our kitchen garden crops find the intense tropical sunlight too bright to endure. Fortunately when required shade is cheap and easy to arrange, as is shelter, but otherwise improving the warmth, and getting more light, is far more difficult.
With our kitchen garden crops we predominantly want to improve their micro-climate in order to extend their season of growth. This is usually to bring forward the start of their season as early crops are most valuable as I dealt with in my last article. Of course it is simplest to improve their conditions by growing under the cover of glass or plastic but this has other effects such as reduced light and increased humidity and incurs high costs economically. While only a small change may be needed to help your plants avoid a late frost and thus mean all the difference between harvest and failure. Warming the soil before sowing by just a few degrees can increase germination levels many fold. Simply improving the general warmth of a garden brings other benefits such as raised levels of beneficial insects and greater nectar flow; both of which are temperature dependent. For our fruit crops it also means better ripening of both the fruit and of the wood and buds.
[It isn't often realised that the climate of westerly maritime Britain is unsuited to many fruits (pears, cherries, plums.....) not just because of the interminable wet but because of the mildness of the autumn and winter. The plant never stops growing in a wet autumn, the mild winter does not make the tree dormant and the wood stays green, doesn't ripen and fades away as the buds open spasmodically in spring. To succeed with these fruits the change needed is to hotter and drier in autumn and longer colder in winter, both hard to arrange.]
However whatever your climate the difference between good years and bad is far greater than the gardener's skill can ever hope to correct but we can hope to improve things at the margin. Now we can always grow under cover, be it cloches, coldframes or something walk in but without going that far we can still make big improvements. I cannot grow tomatoes in the open ground here in Norfolk more than one summer in five but by improving the micro-climate for them I can ensure a good crop every other year. Indeed I never worry about feeding regimes or pest control as most of the skill in getting a crop at all is improving the micro-climate for them and trying to make sure they get as much sun as possible without being blown over or chilled to death.
The easiest and most important way we help enhance our crop's micro-climate is by giving them shelter; this helps simply because plants are warmer with the wind kept off them. It may be on any scale from the shelter of other plants, a few twiggy growths, a ring cut from a plastic bottle, a low fence of woven material, a panel fence or a full hedge. All do most good if they filter the wind rather than block it causing eddies and turbulence. Indeed solid fences and walls are much more use if they are topped off by a trellis and or climbers rather than stopping abruptly.
We often plant on walls and with these the thermal mass can also help as it buffers sudden temperature changes to a small extent -and if it is a badly insulated house wall so much the better. Different walls have different qualities; a brick wall absorbs and gives off more heat more quickly than does a stone wall, and brick can be moistened more easily giving a drier soil, and damper air for longer after rain, than with stone. I use old car tyres to make temporary walls for peach trees; they're cheap and easy to use, and by creating a wall behind the tree I get ripe peaches every year.
Now we all know the importance of aspect; that a wall facing south gives you the most sun in the northern hemisphere. But it's not quite so simple in practice. Although it is true that a south facing wall gets the most sun this is most true in winter when the sun is low. In midsummer the sun is very high when it is midday, almost overhead, so then not so much more direct light actually strikes plants on the south wall. And as the air is clearest in the morning then in mid-summer an east facing wall can be getting as much total light. Against that is the fact that if the sun strikes frosted foliage or flowers it causes more damage than a slow thaw so an east facing wall may be brighter but carries more risk. A west facing wall has the afternoon and evening sun when the air is dustier so it gets less light in total (and in most of Britain it is also the wettest wall as the majority of rains come in off the Atlantic).
But in fact a plant on a south facing, or any other, wall or fence gets less light than it would if it was free standing. The wall blocks off all the light from it's own side, and although it is true there is little direct light coming from the north there is considerable indirect light from the sky and a wall or fence blocks off all light from half the sky. Which is also why a wall or fence helps protect from frost; most frosts are caused by the heat radiating off into the cold blackness of the night sky. As a wall or fence blocks off half the sky the plants are exposed to half as much loss, as well as being aided by any thermal buffering mentioned above.
This radiant frost protection is vastly increased if a small coping projects out from the wall over the plants in the way the eaves of a house do. This also traps rising warm air aiding the plants still further, and prevents much hail and rain damage. With the addition of temporary nets hanging from the outer edge a coping so equipped can keep many degrees of frost off plants on a wall and a small way out from it's base. Against the benefits of a coping it must be added that it further reduces the amount of light reaching the plants and it really ought to be made of glass. Indeed I've been experimenting with simple single glass walls for grapevines; a large second hand glazing unit keeping the wind off does not reduce the light much and brings the ripening forward by a couple of weeks yet does not create the undesirable cramped and close conditions of a cloche or coldframe.
Obviously in most cases a glass wall is not handy so painting white those walls we do employ is almost a necessity as this at least reflects back light that would otherwise be lost. Likewise any area in the garden that is a light colour will throw back more light, a light coloured gravel drive will be significantly better than a black one and a concrete area better still. I even use second hand white epoxy coated radiators for a path in my polytunnel. They are excellent for this purpose anyway but also reflect considerable light back up on to the plants. This is most effective in winter when the sun is low. You could lay white plastic sheet or painted boards to do similar inside or outside a greenhouse or polytunnel just for the extra light.
Naturally it is foolish to try and let more light in if you are lax with the pruning and allow valuable sunlight to be grabbed by less worthy plants. This is most important when the sun is low in winter when just taking a foot off some hedge, bush or tree might make all your greenhouse plants much happier! If the shading is intense and not alterable the answer may be to go up, raising the plants from the floor up on to higher shelves or staging will usually expose them to more light, and under cover to warmer air. On the patio putting plants up on stands can help give them more light but will expose them to more wind and move them away from any warmth of the ground.
One of the other ways you can get more light onto your plants is by changing their inclination, or rather that of their soil or staging. It is obvious that if you have flat staging then when the sun is low the plants must shade each other. Thus a set of staging shelved so that each row of plants does not shade those behind makes a great difference. (A simple method with a few pots is to stand one row of plants behind the other putting those behind on top of inverted empty pots.) On a larger scale I build a staggered pile of straw bales so that my citrus plants rise up off the floor in three tiers behind each other.
In the open garden, or in the greenhouse border, the soil can be sloped towards the sun to place the plants in a similar way as if on tiered staging. But this also makes the sunlight strike the soil at a more direct angle which significantly warms the soil more. Indeed angling a bed only a few degrees towards the sun can make your soil get as much more sun as if it had moved to Spain. This is why it is worth making the effort to raise and angle one small bed towards the sun for early salads and the tenderest crops. And it will be a small bed as the amount of soil you have to find and move to make a slope is immense! Believe me!
I constructed a herb garden generally sloping towards the sun but additionally in a bowl shape held up by the retaining walls with the whole bowl angled towards the sun. This gave some excellent places for putting the tenderest herbs as well as an interesting form but my goodness the amount of earth moving was back breaking!
An easier alternative is to sow and plant in bowl shaped depressions where you have small sheltered slopes for the seedlings whilst small. Indeed these give similar advantages as having ridges and furrows do for many crops because of their well known differing micro-climate effects. Even a rough mulch or a cloddy or stony soil can provide shelter to the smallest seedlings in the right places. Which probably helps explain why self sown plants are so good; they started off where they got the very best start they could find!
Naturally the soil conditions such as the drainage also effect the micro-climate as badly drained soil will stay wetter and take more heat to warm up keeping the air above cooler and damper. And of course the colour makes a great difference and as a darker soil warms so much more quickly then I'm surprised no-one has yet offered a commercial substitute for the legendary soot which has all but disappeared. Now that's an idea.....