Air Circulation
While a little air circulation is a good thing, particularly in avoiding fungal problems in a humid atmosphere, too much – as in strong winds – can cause problems as well. Part of the problem is that plants, even decent sized trees, can be damaged by strong winds, hot or cold winds can exacerbate thermal problems by drying out or freezing sensitive plants. An open area like a front yard will most likely have a high air circulation microclimate, even in a built up area, and require some work to ameliorate.
One of the issues with built up areas is that the buildings themselves and the fences dividing blocks will have an impact on wind speed and direction at ground level. To reduce the impact of strong winds a windbreak can be constructed. It is best if windbreaks are not impervious to the wind, but slow the air down as it moves through the windbreak. To this end they can be constructed from a trees and bushes, a wire screen and climbers or a longitudinal food forest.
This is a pic in the front yard looking south on a windy day, the effect of the wind was considerably reduced by the fruit tree circle down wind of it
Of course the other effect can also be true, if you have a dense planting of trees or shrubs the result can be reduced air movement and the consequent increase in fungal issues. Fortunately, this can be easy to treat just by pruning away some of the foliage of the plants to allow greater air movement though the plantings.
Thinning out thick foliage (like above) can increase air movement, reducing potential fungal problems
We get cold winds from the south at our place, and in the front yard the fruit tree circle has a noticeable effect on wind speeds north of it which impact on the nectarine tree and herb spiral. A strong breeze can become a light breeze in the shelter of the fruit tree circle. In a similar way, the bananas in the banana circle provide shelter from cold southerly winds to the chook retirement village and the worm shed. The sheds, bananas and the mandarine tree likewise provide some shelter to the back of the house for hot northerly winds and some shelter from hot westerly winds also.
The banana circle shelters part of the back of the house from hot westerlies and the chook retirement village from cold southerlies
It can take a while for a perennial windbreak based around trees to grow, so while that is being put in place, a windbreak can be constructed by building a wooden pailing fence, with every second pailing removed, upwind of the microclimate to be protected. Also, when planting a windbreak, plant vines, trees and shrubs at the same time. The vines will grow quickly, creating an initial windbreak and can be controlled by pruning, as the other trees and shrubs grow more slowly to form a permanent windbreak.
Slope of the land can also have an impact so if you live below high ground, in cold weather cold air frost can move downhill towards your property. Low growing shrubs can be planted uphill to protect more delicate plants lower down, causing the frost to drain either side of the planted shrubs.
Hay bales can be used to create a calmer microclimate for low plants just starting out if placed upwind of the plants to be protected. Once the plants are established they will not need the protection and the hay bale can be allowed to rot down and provide organic matter.
Water
The thing to do in developing damper microclimates is to make absolutely the most out of every millilitre of rainwater falling on the property and ensure that it is either stored in tanks, ponds and/or the soil.
Tanks take rainwater off a building roof and store it for later use, reducing reliance in reticulated water supplies. They also have an impact on microclimates by storing energy from the sun as mentioned above under ‘temperature’. Water from tanks can be used to top up ponds when rainfall is low, and to keep plants alive when the macroclimate wants to dry out our microclimates.
Our bath pond growing arrow and water chestnuts 2015
Same area 2023
Ponds can be set up to be filled directly by rainwater, either via runoff from the ground or by connection directly to a building downpipe. Ponds will also impact microclimates by storing heat and increasing the humidity in the surrounding area. A pond will increase opportunities for biodiversity by providing water for birds, insects and habitat for fishes and/or frogs. Bog plants like arrowleaf, water chestnut, water spinach and many others can be grown in the damper microclimate of a pond or pond edge, depending on how things are set up.
There are a number of ways of keeping rainfall on your land so that it sinks in rather than runs off, depending on the slope of the land. The greater the slope, the quicker and easier it will be for rainwater, particularly heavy falls, to exit your land before it can sink in. Generally speaking, storing water in the soil is the easiest and best option, hence the advice about moving water is to slow, spread and allow it to sink in.
Some ways of slowing, spreading and sinking rainwater runoff include –
Swales – a swale is a shallow trench dug across the contour, where the spoil from the trench is built into a mound on the downhill side of the trench. The trench may be left open or filled with material such as wood chip to reduce trip hazards. The idea is that water draining downhill on the land in question hits the swale and the water is directed into the soil rather than being allowed to run off. Where the land is steeper than 15⁰, swales are not recommended due to the possibility of water saturation of the soil causing slides. The mound may also be planted out with beneficial species to take advantage of the damper microclimate created by the swale.
Fish Scale Swales – These are a small, curved swale, or series of curved swales, dug on the contour rather than one long swale. They are set up so that when one overflows the one each side of it farther down the slope will catch the overflow. They work very well to create a damp microclimate for a series of trees, with one tree being planted per fish-scale swale.
Fish scale swales put in as part of a school garden
Rain garden – This is a depression in the soil or basin filled with plants that can survive temporary flooding, usually built at the lowest point of a gentle slope. It may also be fed by a roof downpipe. It allows water to be slowed and spread so that it sinks in rather than running off.
Retention basin – This is sort of like a rain garden without the plants. It is designed to collect water that would otherwise be runoff and allow it time to infiltrate into the ground.
Drain Chimney – This is a hole dug down into the earth where a downpipe drains, filled with a pit case with a drain matting sock attached and filled with gravel. It provides a way for rainwater to get into the soil without running off, thus creating a damper microclimate in that area. Also, when the drain chimney overflows, the energy gained as the water falls through the downpipe will be dissipated when it hits the drain chimney, meaning the water will have been slowed, giving it opportunity to spread and sink.
Drain chimney - constructed
In place
Operating
Terracing – this is where a flat area, or areas, are dug into sloping ground. While this requires earthworks and so is not a cheap solution, it only has to be done once. With reduced or removed slope to the ground any rain hitting the terrace will sink in than run off. The terrace also provides a great growing area for beneficial species.
Permeable paths – are paths made from wood chip, gravel or other loose aggregates which allow rainwater to percolate directly into the soil, as opposed to solid concrete or asphalt paths which result in runoff. A permeable path can be used around a building to conduct rainwater into the soil where no gutter is provided. The area where the rainwater falling from the roof meets the ground would rapidly become compacted or eroded and allowing the water run off the property rather than percolating onto the soil.
Our permeable path, taking water from the back deck
Other ways of keeping the water where you want it include –
Mulching - has a whole stack of beneficial actions for plant growth but also when it comes to creating a damper microclimate, generally by allowing less evaporation and more infiltration. Mulch provides a barrier between the hot sun and the soil surface, reducing water loss due to evaporation, a mulch can reduce evaporating losses from up to 80% to 10% or less. Also, ridiculous as it sounds, the cumulative impact of rain drops can cause a crust to form of the top of soil, resulting in rainfall running off instead of soaking in.
We use straw mulch on annuals, wood chip on perennials
Shade – The lee of a building or structure that provides shade, particularly from the harsh western sun, will allow the soil to stay damper for longer in that area from rain or due and maintain soil moisture. Planting in that area will take advantage of a damper microclimate. Obviously, shade is not an unmixed blessing and plants will need at least some direct sun to grow, fruiting plants will require more and leaf crops less.
Too much?
The thing with water is that while not having enough is a common problem, occasionally you can have too much. Clay soils in particular can puddle and become puggy, giving plants growing in that soil ‘wet feet’. Some plants cope well with wet feet but others, like citrus can find wet feet difficult to survive (I learned this the hard way!). If you are looking to plant perennials or annuals which prefer a drier microclimate, then using raised beds and growing areas to get your plants above the water can be worthwhile.
Another option, particularly if your issue is a clay soil, addition of calcium salts such as calcium carbonate (which will also raise your pH) or calcium sulphate (which won’t) can be spread on the soil at a rate of a handful per square metre, when you are cultivating the soil or on top, but before mulching, if you don’t cultivate. It will take longer to be effective if spread on top of the soil rather than incorporated by digging it in, but it will still work.
The last word
If we are serious about our gardens, and for me that also means being serious about growing food, some understanding of what a microclimate is, how the concept applies to our own growing areas and indeed the particular microclimates that exist in our own yards is vital so we can take advantage of them. Also knowing that it is possible to modify and/or create microclimates means that in Jamie’s words, we will be able to “…provide protection from what makes the plant suffer, and serve up the elements that make it thrive.”
Links
Microclimates Part 1: What are they and why are they important?
Microclimates Part 2: Identifying your microclimates
Microclimates Part 3A: Modifying and creating microclimates - Temperature and Light
