Once there is some understanding of the microclimates in the area for which we are responsible, it is then a case of working out the sorts of plants, both productive and (shudder) otherwise to be grown in that area. As Jamie Durie in his book ‘Edible Garden Design’ says – “To create a true microclimate, look at what makes your chosen edibles suffer or thrive. Then, all you need to do is provide protection from what makes the plant suffer, and serve up the elements that make it thrive.”
The first thing is to match up any existing microclimates with the prospective plant list. It makes much more sense, when down the back of the yard there is a place that it always soggy, to seek out plants that will do well in that microclimate then spend time effort and money draining it to grow something else.
It now becomes a case of putting plans (plants?) in place to change or create microclimates that will ‘provide protection……..and serve up elements that make them thrive’.
Temperature
Generally, setting up a temperature microclimate means that you want to keep the cold places warmer and/or the hot places cooler.
Cool places warmer – There are a number of ways of doing this, generally using a thermal mass of some description. Thermal mass is the property of a material to absorb energy from the sun in the form of heat and then re-radiate that energy, causing the area around the thermal mass to remain warmer than the larger surrounding area. One obvious source of thermal mass is a house, or to a lesser extend a shed, depending on its material of construction, but you will already be aware of those. So to increase thermal mass in an area where there isn’t any one of the most useful materials is water.
Three water filled baths (2 x constructed wetland and 1 x pond ) increase winter temperatures in this microclimate
Water has a number of advantages when in use as thermal mass. It has one of the highest specific heat capacities of common substances so it stores a large amount of heat per degree of temperature increase, it is easily stored and can be free, or at least available cheaply and the water can also be used for other things. To get water storage in the area where the microclimate is desired it can be either stored in drums, water tanks or other containers or it can be stored in the form of a pool or pond. The thermal storage impact on the microclimate will greater, the greater the volume of water is stored in the tank(s) or pond(s).
Plastic house (Pristine, when first constructed)
Another way of creating a warm microclimate in winter is the glass or plastic house, the larger sizes of which will be more effective and maintaining temperatures for longer overnight, regardless of which a glasshouse will provide frost protection for tender crops. The glasshouse may also be enhanced by including some thermal mass in the form of brick structures within it or, more easily, dark drums filled with water. It will allow the growing of out of season crops like tomatoes.
Water-filled black pickle drum inside plastic house to raise night-time temperatures in winter
The glasshouse can still be used in summer but it must be modified to reduce the heating effect of the sun (if we do not do this we regularly get temperatures of 60⁰C or higher in summer). This can be done by painting the glass panes of a glasshouse white with limewash to reflect light and heat or covering either glass or plastic house with shade cloth, preferably 50% or 60% so enough light gets in for the plants to still grow.
Plastic house (not so pristine) with 50% shade cloth covering to reduce daytime temperatures in Summer
Warm Places Cooler - Water can also cool the surrounding area in summer, particularly if it is couple with the shade effect of trees and open water (ponds as opposed to tanks) will also raise humidity around their microclimate, supporting plants that do well in a higher humidity environment.
Trees will also produce a cooling effect in summer due to both shade and transpiration on hot days, but the downside is, of course, that they will take a while to mature and provide the microclimate that is desired.
Over the years we have noticed the temperatures increasing as well as the intensity of sunlight increasing and have found the growing vegetable crops in high summer to be getting more and more difficult. To get around this we have modified the microclimate of the areas where we grow annual vegetables by setting up a framework and the covering the framework with 50% shade cloth. We generally put the shade cloth in place mid spring and remove it in mid-autumn as a rule but there may be some variation of the timing depending on the expected weather.
Seedling sun protection frame to reduce light/heat impact on seedlings
When we started growing on a year round rotation over 15 years ago I made some frames to go over seedling when they were planted out in summer, but this proved, after a while, to be not enough so we developed the shade cloth covers for most of the area. We do leave some areas uncovered because we have noticed that some plants, like corn, actually do better without the cooler microclimate of the shade cloth.
Light
Generally the problem with light tends to be not enough, rather than too much but even so a low light microclimate for plants adapted to that environment is not too difficult to come up with. One option is to plant trees which will provide dappled shade over the desired area, such as Tahitian lime, lemon myrtle, grevilleas and lemon scented gum which are fast all growing. Another option is to grow creepers over a frame covering the desired area such as passionfruit, grape or star jasmine, the downside being they will need to be managed by training and pruning to get the desired degree of shade.
Protection from strong light and heat of the western sun
Structures can also be put in place and then covered with shade cloth, as mentioned above, to reduce the amount of light and heat in high summer, creating a cooler and darker microclimate. Shade cloth comes in two different types: knitted or woven and is available in various colours.
Knitted shade cloth allows more airflow than woven so that it will not trap heat as much as woven shade cloth. Knitted shade cloth is also lighter and therefore easier to install and is also more resistant to fraying and wind damage than woven shade cloth. Also it is important to note that shade cloth is produced in a number of ‘densities’ expressed as a percentage of light that they block out, vegetables and fruit grow best under 30% to 50% shade cloth. Vegetables also do best under green or black coloured shade cloth whereas some fruits like apple, fig and guava trees do better when white shade cloth is used.
50% knitted shade cloth over the entire veggie patch means we get a harvest even in high summer
Where there is a lack of light in an area the options are somewhat reduced. One way is to just accept that you have a shady microclimate and go for plants that thrive, or at least survive in shade; another is to remove the object causing the shade. Where this is a house or shed or is a large tree that is on a neighbour’s property or protected by a council tree preservation order, there may not be much option.
However, one option is to set up some sort of reflective surface which can reflect sunlight into the shaded area, providing a lighter microclimate than was available previously. Obviously the more light reflected from the surface, the more growing options will be possible and using mirrors can provide excellent light reflectance. The downside of using glass mirrors are that they can be expensive unless bought second hand, they are heavy and difficult to move around and are somewhat fragile. Another option is to construct a light frame out of wood and then affix mirror surface Mylar sheeting (think ‘space blanket’) using double sided tape. This is light and cheap to make but can also be somewhat fragile if exposed to high winds. A third option is thin sheets of mirror surface stainless steel which is not as heavy as glass and is very tough, but it is also very expensive. One of these options may be worth thinking about in a shady microclimate where a sunnier microclimate is desired.
Microclimates Part 1: What are they and why are they important?
Microclimates Part 2: Identifying your microclimates
