Written by Doug Crouch
In the book Introduction to Permaculture, Bill Mollison succintly present ways in which we can accentuate microclimates to enhance our systems. Sepp Holzer, the Austrian Rebel Farmer, instilled much knowledge on this topic for me as well in 2009 during a workshop.
Much research has been done on the topic by Permaculturists over the years both small and broad scale. One site that was based all around micro-climate planting was Edible Tree Crop Farm (Nelson, New Zealand), which was planted out by Dick Roberts starting in the late 1960’s.
This denuded landscape was transformed into one giant 300 acre food forest and I was fortunate to work there for nine months in 2007. I was given tours by Dick himself, still sprite and agile enough to show me around his old farm while he was in his late 80’s. According to Darren Doherty, this farm was very influential on Bill Mollison and David Holmgren in their understanding of Permaculture. Dick had been planting trees, running sheep under them, and working with invasives for many years by time they visited in the 1970’s.
Below is a look at the topics that Bill Mollison outlined in the before mentioned book, my experiences with those and the influences of the teachings of Dick Roberts.
The direction in which a hillside faces, largely determines the microclimate that is present on any given site. Classically, we talk about hillsides that are north facing, south, east or west. Each has their advantages and disadvantages.
For instance the North side can be a bit cooler and often times more moist. Where the South side is hot and the West side is hot and dry. There is also combinations like a Southwest facing hillside, which is the slope that affords much heat for us trying to extend seasons in the temperate ranges or in the borderline sub-tropics. Hillsides at Edible Tree Crop Farm were North facing but that was like our South facing here in the Northern hemisphere. This allowed us to push the envelope with being able to grow subtropicals like Avocados, Macadamia, and Tamarillos to name a few.
Dick taught me that, if you want to grow Stone Fruit in temperate regions, putting them on the North side of the hill is a good idea. By time the fruit begins to ripen the sun is so high in the sky that it is not delayed, except on the most extreme terrain. However, the ground warms slowly on the North side of the hill because of the low winter arc and can delay flowering.
If flowering is delayed, then the late frost presents less of a chance to kill the young fruit or flowers. This can be the difference between plums and peaches in your picking basket a couple months later. Be careful with East facing slopes with Stone fruit as the flowers can be damaged by frost when they are illuminated early in the morning by intense sun which normally happens after a clear, cold night.
Cold Air Drainage
Cold air behaves much more like molasses than water in its drainage pattern. Water finds a path of least resistance and snakes its way through a landscape based on low points. However, when cold air finds low points or blockages, it pools and becomes sources of frost and frost pocket development.
This is a problem for growing our tender annuals like tomatoes and peppers for food production. Careful examination over time will allow you to see these patterns and know that structures, plants, and earthworks that you design in, can lead to frost pockets as the site evolves.
Furthermore, steep hillsides inherently have better frost drainage, which was another feature of what made Edible Tree Crop farm a sub-tropical microclimate. Imagine your wrist and the angle which you would pour molasses. If the angle is shallow then the molasses will move extremely slowly. If the angle is much greater it gets a chance to pick up speed and pooling effect is lessened.
As discussed in other parts of this climate chapter, the ocean plays a pivotal role in the formation of landscape producing what is called the “maritime effect”. The ocean through its large bank of energy –known as thermal mass– tempers climates from extremes.
On a smaller scale lakes and ponds can create a similar effect. Water is the worlds greatest source of thermal mass, yet another amazing quality of this living and life-giving substance. This means it can retain heat and cold and re-release them when temperature switches occur. This can create a small frost-free area for a longer period around it, thus giving a bit of a season extension.
Furthermore, light is reflected off of the water surface. Wine growers near rivers and lakes have been taking advantage of this ripening help for centuries now. Appropriately placed ponds near houses can also give extra solar radiation for warming the house due to the reflection. This was another factor that made Edible Tree Crop Farm sub-tropical as the winter sun was perfectly reflected off the bay and onto the hillside. Finally, ponds and fountains can also diffuse humidity into the air and can create cooling action in hot, dry climates.
Wind can be a major player of climate as it can bring drying, cooling, and damaging winds to crops and houses. In India, we would water at sunup every morning and within a few hours, the moisture was wicked out of the poor soils from the intense sun and drying winds. It really was like a hair dryer being turned on and the plants would suffer greatly daily from it. Also cold winds can increase your heating bills by sucking the heat right out and infusing the cold. A well placed windbreak for both of these situations could drastically help.
Walls, houses, greenhouses, pergolas and other structures can influence the microclimate of a site. Pergolas or trellises that get vegetation above ones head can create the right microclimate for an outdoor social space. Without the shade, the area would be unfit for socializing but with a deciduous vine selection it could even be used on a sunny winter day. Similar to a pergola, in India, we built thatch roof structures with a non densely packed roof to create dappled sunlight below. The plants greatly benefited from this technique as the dry tropical sun was just too much for the vegetables.
Also greenhouses and cold frames (a much smaller version of a greenhouse that fits over a bed) can be employed to extend season. Greenhouses against walls can be a great way to capitalize on two parts of this topic as brick and concrete walls are also high in thermal mass. The thermal mass can re-radiate heat and create a frost-free area around a building. Buildings can deflect cold air drainage and when the walls are south or southwest facing, as I have in my garden, the growing season of a bed against that wall is longer than beds away from the wall. The soil temperature stays up and frost is eliminated. I have had Jalapeno plants still ripening fruit in November long after our first frost day.
See below the design of the site and note the garden up against the southwest facing wall. I have also seen greenhouses be used in the tropics to keep moisture off crops. In some areas, this should just be considered winter as the other 10 months of having plastic above your vegetables will be tough growing conditions.
Using rocks in terracing also has a similar effect as stones hold the thermal mass. In my gardens at my folks place in Ohio, USA, we have stone terraces that warm nicely in the spring. Holzer famously used large stones inside his ponds that would stick up out of the water to absorb sunlight heat energy and radiate it out into his ponds. This gave him a longer growing season in his aquaculture systems allowing for a more economically profitable situation.
Bill Mollison points out in his section on microclimate that soils have little bearing on microclimate. A darker soil will absorb more heat, warming its temps earlier in the year. The main thing that soils do for microclimate is their ability to hold moisture. Those that have a higher organic matter percentage hold more moisture, thus creating a more stable growing environment for microbe and subsequent plant life. Ensuring the rebuilding or maintaining of fertility is important for creating a space of abundance.
If the soil has been capped by something such as concrete, it will create a microclimate in the area. My rosemary is now three years old and everyone marvels at it. It is basically surrounded by concrete and I believe the extra thermal mass gives it the conditions to thrive as well as being protected by an L-shaped enclave in front of the house.
To mitigate some of these other factors, vegetation is used to create a formidable microclimate. Pergolas are just some wood unless you get a vigorous vine going and then you have good social space. Often times people also ask about trees to shade the south side of a house. I would say they are better off on the western side but do the research with how big they get and imagine 50 years from now. Vines are less invasive to foundations and grow much quicker. I am using grape vines and hardy kiwi in temperate suburbs but also wysteria works really well.
Again with wind, a windbreak is needed to slow the drying and cold winds. They should be designed for multiple functions and created with an equilateral triangle shape rather than just one line of trees. This helps to lift and disperse the wind rather than causing turbulence on the backside from the overback jet pattern. Don’t forget that -if you desire winter protection- you will need to use those species that don’t lose their leaves. Careful planning has to happen so trees don’t shade the house in the winter.
Another vegetation strategy is one that you can see again in the same picture below from Edible Tree Crops sister farm that I was charged with creating a design and installing the first implementation phase. It has what is called a sun trap and serves multiple functions in this particular context.
It served as a windbreak, deflects cold air as it drains down hill from its organic shape, and traps heat as it is placed on sun facing hillsides with an open arc. It was a great pre-existing feature that allowed us to grow Avocados in the backyard, which at that height in relation to the valley is not normally possible. Some plant and mushroom species will also benefit from the shade of other plants. This is also true for animals as a shady place for them to rest and windbreaks for them will give them better health.
Having a Savannah like pasture system with tree belts is a great way to provide a better microclimate for a pasture. Legume trees like Honey Locust in Temperate realms, Acacias in drylands, and Luceana in the tropics present the classic umbrella image of African rangelands. By growing these above the grass below, climate mitigation is possible on a small and broad scale.
Forests in general mitigate climate as during my PDC, the fields of Lost Valley were tough to be in, both in the day and at night. Upon arrival in day, you were always looking for a shade tree while at night the cold air pooled. In the heat of the day we would flee to the forest where there was a stream and shadow and at night we would be given a warm blanket from the trees as well.
Written by Doug Crouch
Header Art by Anita Tirone