Shantree Kacera, D.N., Ph.D., who practices and teaches veganic permaculture and forest gardening at The Living Centre in London, Ontario, which is located in the heart of Carolinian Canada, kindly wrote this article.
What is a Microclimate?
A microclimate is an area that due to its situation in the landscape may be warmer or colder, drier or wetter than the rest of the property. It is a play of the elements: air, sun, water, earth and space. It is basically a local atmospheric zone where the climate differs from the surrounding area. This may refer to areas as small as a few square meters (for example a corner of your garden) or as large as many square kilometers (for example a valley).
By understanding the theory behind microclimates you can often grow plants that are normally tender in your zone. You may even be able to grow those plants that need a bit more chilling than your climate naturally provides.
If your garden is more than a few years old, you may find yourself taking up plants and moving them to areas you think they’ll thrive better. Experimenting with and observing your plants will teach you about your land’s unique variations in soil moisture, light, and soil acidity. You can use this knowledge to assemble communities of plants that are well adapted to your garden’s microclimates.
Identifying microclimates by observing moisture and shade
For garden microclimates, think of moisture and shade. Using just these two factors can show you how to make a microclimate work in your garden. Each of the following is an example of a microclimate:
Dry Soil/Lots of Sun: Plant drought tolerant plants. It is a great spot for a Mediterranean herb garden.
Dry Soil/Shade: This is usually found under large trees. These areas may be cooler than the surrounding areas making them ideal for cool weather plants that wither in the sun.
Moist Soil/Lots of Sun: Here’s the spot for a water garden or bog garden. Plant anything that doesn’t mind wet feet.
Moist Soil/Shade: A woodland community. This is the perfect place for wild ginger, wild leeks, ginseng, goldenseal, black cohosh, blue cohosh, etc. For all those shade loving plants that love having their feet wet.
5 conditions that affect microclimates
- Patterns of Light
- Humidity Distribution
- Air Circulation
- Soil pH & Structure
We all too rarely think about temperature in terms of what plants we can grow. The key fact is that when the thermometer says it is 20 degrees outside, it is 20 degrees at the thermometer. But that doesn’t mean that it is 20 (°C) degrees everywhere in your garden. Take that thermometer over to a shady spot and see what it says. Sunny spots are called hot spots and almost invariably have the highest temperatures. This is usually where cats like to lie around.
We also know that hot air rises - but usually only think about that in terms of indoor heat and hot-air balloons. But it is also true outdoors. If your land slopes, like mine does, then if you carried that thermometer around the yard you would discover that the higher the rise, the warmer the temperature. In the dips and valleys temperatures are slightly cooler.
So, the more tender the plant the higher it needs to be and the more sun or reflected heat it needs. If you try growing it in a dip in your garden - probably a frost pocket – well, you know what that means.
2) Patterns of Light
A microclimate is also affected by the amount of sunlight an area receives. Areas that get little or no sun tend to be cooler than those that receive a great deal of sun. Many factors can affect the amount of sun an area receives, including the following: buildings, soil mounds, walls, fences, trees and other vegetation.
Shady areas tend to hold moisture for longer periods of time and are consistently cooler than the sunny areas of your garden.
Some of these elements create different amounts of shade seasonally. Trees lose their leaves and suddenly an area gets more sunlight than it did in summer. In winter the shadows are longer and the days are shorter because the angle of the sun is lower (about 30 degrees) than in summer when it is at the higher angle of about 75 degrees.
So, when we take these various factors into account, the slopes that face south or southwest are warmer than those facing north or northeast. This is because they will receive the sun most directly - but they stay warm because, as we saw above, heat rises while the cooler air literally slides down the slope and settles at the lowest point.
A south facing built-up soil mound or stonewall (perhaps about 2 meters high) can absorb the heat and light of the sun during the day and then slowly release the heat at night. If this same area is protected from winds it can actually be a microclimate as much as 10 (°C) degrees higher than in other spots in your garden!
Conversely, plants that languish in the hot summer can survive happily in a shadier place with more humidity and slightly damper soil.
You can somewhat adjust the amount of light and heat a wall may create with the colors that you use on them. Keep in mind that white reflects heat back at the plants while black absorbs the heat.
One way to create a warm microclimate for early spring or late fall is to put shade trees on the northern side of your garden. This will increase the amount of heat you get from the sun, by absorbing the heat during the day and then emitting it at night.
3) Humidity Distribution
Water also affects the amount of heat or cold in an area. The presence of larger bodies of water nearby – such as the great lakes - creates a more moderate climate. But even a small pond can affect the temperature of a portion of the garden to a small degree. The lake or pond sends moisture out into the air. That water vapor acts a bit like a miniature greenhouse effect as it traps the infrared radiation reflected from the earth.
As long as there is vapor in the air then, we are getting those reflected infrared rays. The air that takes on moisture from your pond is literally trapping heat. So plants near your pond will enjoy some extra humidity during the day - and if you get out that thermometer again you may find that during the day the temperatures there are warmer. This explains why I am able to grow pecans, peaches, apricots and almonds (supposedly not that hardy in this region of southwestern Ontario) next to our large pond.
Plants also release humidity into the air. In your garden you can take advantage of that by putting drought tolerant plants at the edge of a grouping and those that need a higher humidity in the center of the bed. That way the plants that need more moisture will benefit from that released by the drought tolerant plants that surround it.
4) Air Circulation
As mentioned, hot air rises, which means the reverse is also true - cold air sinks. Look around your garden early one spring morning or late autumn and see which areas have frost on the lawn. They are probably all the depressions in the land. It is easy to see that wherever the ground slopes downward will most likely be frosty - whereas the high points are quite frost free. The point being: plants that need heat belong on higher ground.
Wind is another factor that affects the microclimate. Plants that are sheltered from winter winds survive better than those that are right out there getting the brunt of them.
Plant trees or shrubs in areas that get high winds if you need to create an area that is safe for those tender plants. We can grow persimmons and almonds that are allegedly only marginally hardy in zone 7 and they are quite happy in our zone 6 garden. We are growing them between a windbreak and a hedge of tall evergreen trees – and they are planted at what is the highest elevation on our property. They flourish for us because of the protection from wind as well as the heat and light reflected from the soil mound we have been creating over the years.
5) Soil pH & Soil Structure
Soil acidity is measured on the pH scale. A lower number equals higher acidity, and because the scale is logarithmic, each number is ten times more acidic than the number above it. Neutral pH is 7, and plants vary in their tastes and tolerances. Many traditional garden plants thrive the best with a soil pH between 6.5 to 7.0. You can learn the pH of your soil using testing kits that are easily found at garden centres. Check the pH of the soil in several different areas of the land, as it can vary considerably. Soil acidity is influenced by local sources of acidity (like many evergreens) or alkalinity (such as limestone). Though there are many naturally occurring substances that you can use to change your soil’s acidity, you can avoid a never-ending battle against your garden’s characteristics by choosing plants that will enjoy the soil your garden offers.
Learning about the structure of your soil will also help indicate which plants will prosper. Soil structure can be determined by how it feels between your fingers. Sandy soil will crumb easily, clay will hold together like a ball when slightly moist. The majority of plants will thrive in a loamy black soil. Loam is a rich soil consisting of a mixture of sand and clay and decaying organic materials. It is quite high in nutrients to grow healthy plants.
Creating a microclimate in 12 easy steps
“You can fix all the world’s problems, in a garden. You can solve them all in a garden” Geoff Lawton, PDC Designer, Teacher
Take a look around your garden at the areas described above. What is a characteristic of microclimates that you can modify or enhance? Can you build a rock garden in that dry sunny place? Large rocks or boulders absorb heat during the day and release it at night. They can be used to block the wind. A plant from one zone warmer might be able to thrive in such a place.
Choose plants that might benefit from creating microclimates in small pockets of your garden. You might extend your growing season by planting frost tender plants on the south side of your house using the sun and shelter of the building, or by creating a microclimate earth mound for them.
With a little time and thought, you can figure out how to make a microclimate work for you and your garden. Here are 12 basic steps to help you create a microclimate oasis.
Step 1 Garden Layout
Know exactly where the sun is in your garden, morning and evening, and in different seasons.
Step 2 Elevation
Exactly where your garden is on a hill affects levels of temperature, light, and wind.
Step 3 Soil ph & Structure
Soil types react with climate in various ways. Structure can be modified to affect microclimate.
Step 4 Plants
Choose plants from climates and habitats similar to your own garden for lower maintenance and good success rates with plants.
Step 5 Location
Use your house walls, soil mounds, garden walls and fences to best advantage when choosing plants.
Step 6 Wind
Plan to baffle, filter and drain rather than contain wind.
Step 7 Heat
Make use of available storage heaters in your garden – soil mounds, patios, buildings and walls.
Step 8 Cold
Position kitchen gardens so that they receive sun to warm up the soil early in the season, avoiding frost pockets.
Step 9 Planting for Hot and Cold
Use plants from hotter climates in warm south facing areas and near hot spots.
Step 10 Work with What You Got
Take advantage of what you already have, use the resources at hand.
Step 11 Be Curious!
Nothing happens or changes unless you are truly interested.
Step 12 Have Fun!!!
Without this step the ones above become abandoned.
Remember: The first and last principle is observation. By looking closely you can find those small microclimate pockets in your garden.
Forest gardening and microclimates
“Forest Gardening is seeing through the eyes of an ecologist.” Forest Gardening: Roots of Regeneration
The beauty with 3-dimensional forest gardening is that you can easily distinguish three microclimate zones: a sunny spot, a forest edge and under the shade of a tree.
Like natural forests, a forest garden can integrate some clearings with many edges where there is enough light for growing most vegetable crops. It will also use the space efficiently by having plants growing at all the layers such as:
- Canopy: larger fruit or nut trees.
- Small trees: semi-dwarf varieties of fruit trees or other smaller food producing trees.
- Shrubs: may be fruits and nuts on dwarfing rootstocks, bush fruit such as currants, gooseberries, etc.
- Herbaceous perennials: such as herbs, flowers, insectary plants, nutrient accumulators.
- Ground covers: may be creeping plants such as creepy thyme, strawberries.
- Vertical layer: may be climbing berries, kiwis, vine crops.
- Rhizosphere: can be used for shade-tolerant root crops such as daikon, horseradish and many bulbs.
- Epiphyte layer: such as mosses and lichens that grow on trees that can be harvested and used as mulch or craft material.
The concept of forest gardening is to design a system that uses a diversity of plants to produce food and other products in a sustainable way. Such a system is resilient in the face of climate irregularities and pests and diseases, utilizes growing space to a maximum, benefits the environment by reducing atmospheric carbon dioxide, and provides other less tangible, moral and spiritual benefits. When creating a forest garden, you are creating a diversity of microclimates for a wide variety of plants, while also creating a resilient garden for the future.