Combat Zone Envy - Make Microclimates
by Carol Wallace
No matter where a gardener lives they always seem to think that people in other climate zones are better off that they are. Those people in cold climates envy the lush tropical plants that warm climate gardeners can grow so easily, while those in warm climates wash nostalgic about the lilacs and tulips they used to grow back up north. We somehow manage to live through these disappointments with fair good humor. The zone envy that really turns us green is that of the people one climate zone different that we are - so near, yet so far away.
That one zone difference can be a killer. We go to the nursery and see the most gorgeous plants - love at first sight. We know exactly where it would look wonderful in our yard. And then we check the care tag.
Instant gloom. It's hardy in the next country - but not in my yard. At least that's what most of us believe. I'm not so easily convinced. For one thing, I have gambled several times on plants that were supposedly a bit tender for my area and had them survive with flying colors. Often the plant really IS hardy in my climate zone - but not enough people have tried it and reported success with it to convince the experts.
That's what happened with my first hellebore. I had seen them in Europe, blooming on Christmas day. I HAD to have one. Back then they were not easy to find, but finally I saw one in the Winterthur catalog. Sadly, it was listed as being hardy only to zone 7. But I just HAD to have it.
My local nursery owner told me that I might possibly succeed with it if I planted it near the house, which would give it some shelter and also provide it with a little extra warmth from the house. I followed his advice - and now, ten years later that hellebore is a fine, strong plant that is blooming as I type this.
I guess a lot of other colder-climate people were as foolhardy as I was. The next thing I know that Helleborus niger was being rated as hardy to zone 4. All those cold climate gardeners who were growing it without problem can't be wrong
So if you see a plant that you really want, you can always gamble that the experts haven't really tested the limits of its cold hardiness. That's one way to help cure some cases of zone envy.
Others are not so easily overcome. Some plants that are rated as hardy to zone 7 really aren't hardy in zone 6. But that doesn't mean that you can't grow them. It simply mans you need to seek out a microclimate on your property and situate the plant there.
What is a microclimate?
Basically it's an area that because of its situation in the landscape may be warmer or colder than the rest of the property. When the nursery man told me to situate my hellebore near the house he was recommended a site near the house's foundation because it is a microclimate - an area likely to be warmer and more sheltered from freezing wind than more open areas of the property.
If you understand the theory behind creating a microclimate then you can often cheat and grow plants that are normally tender in your zone. You may even be able to grow those plants that need a tad more chilling than your climate naturally provides.
Four conditions that can help you to create a microclimate in your yard:
- patterns of light
- humidity distribution and
- air circulation.
I'll explain a bit about each of these and give some suggestions as to how you can take advantage of them to extend the range of plants you can grow. Let the neighbors have zone envy - let them be envious of you!
We know this about the outdoor temperatures, but all too rarely think about what it means in terms of the plants we can grow. The key fact is that when the thermometer says it's 90 degrees outside it is 90 degrees at the thermometer. But that doesn't mean that it is 90 degrees everywhere in the yard. Take that thermometer over to a shady spot and see what it says. Shady spots almost invariably have lower temperatures.
We also know that hot air rises - but usually only think about that in terms of indoor heat and 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.
The lesson here is clear - the more tender the plant the higher it needs to be and the more sun or reflected heat it needs. Put it in a dip in the land - probably a frost pocket - and you are sending it to its doom.
Patterns of light
The temperature, and thus the 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.
- other plants
- even where you park your car
Shady areas are not only consistently cooler than their well-lit counterparts - they tend to hold moisture for longer periods of time.
Some of these elements create different amounts of shade seasonally. Trees lose their leaves and suddenly an area gets more light than it did in summer. This is why we can plant spring bulbs in a tree-shaded spot - they bloom before the trees leaf out.
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.
What all of this means is that we are able to draw some conclusions when we take these factors into account, such as that 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.
Walls that run to the east or west reflect heat and light toward their south sides, which means that they create shade on their north sides. The side with the most light is the warmer side. In my own garden I have an old stone wall with remnants of whitewash that reflects the sunlight and heat in summer. It actually got too hot for the simplicity roses I had planted there. Across the way the facing bed has no stone wall - and the same plants look happier.
A south-facing stone wall that absorbs the heat and light of the sun during the day and then slowly release it at night. If this same area is protected from winds it can actually be a microclimate as much as 8 to 10 degrees higher than in other spots in your yard!
Conversely plants that languish in the too hot summer can survive happily in a shadier place with more humidity and slightly damper soil.
You can manipulate the amount of light and heat a wall may create somewhat with the colors that you use on them. Remember that white reflects heat back at the plants while black absorbs the heat. If you don't believe me, try wearing one black and one white sock outside in summer and tell me which one gets hottest.
One way to create a cool microclimate for summer is to put shade trees on the southern side of your property. This will lower the amount of heat we get from the sun. If you want more heat then make sure there are no trees, buildings, etc. between your heat-loving plants and the sun.
Also, the more paved area you have - especially with light-colored paving - the more heat it will reflect. Reducing the paving and adding more grass or more plants will help reduce the temperature.
Water also affects the amount of heat or cold in an area. I remember being flabbergasted when I discovered that Anchorage, Alaska had weather as warm or warmer than my Pennsylvania garden. Or that Boston, which is north of me also was a zone warmer. The difference is partially due to the presence of huge bodies of water nearby - oceans, in these cases. But even a small pond can affect the temperature of a portion of the garden to some degree, The pond or lake 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. SO 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 calla lilies (allegedly not hardy in my area) next to my big pond without digging them up in the fall. They stay in the ground year round and flower faithfully each summer with no protection except their pondside home.
Plants themselves also release humidity in 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 more drought tolerant plants that surround it.
Air Circulation Remember what I said earlier about hot air rising. The reverse is also true - cold air sinks. Look around your yard early one autumn or spring morning and see which areas have frost on the lawn. They are probably all the depressions in the land. Our yard isn't level anywhere, so it's easy to see that wherever the ground slopes down we have frost - whereas the high points are quite clear. So the lesson is clear - plants that need heat belong on higher ground than those that prefer cold.
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. So slightly tender plants need as much wind protection as possible.
Put trees or shrubs in areas that get high winds if you need to create an area that is safe for tender plants. I am growing bamboo that is allegedly only marginally hardy in zone 7 and it is quite happy in my zone 6 garden. . I am growing it between a stone wall and a hedge of tall evergreen trees - and it is planted at what is the highest elevation on my property. It flourishes for me because of the protection from wind as well as the heat and light reflected from the stone wall.
Pay attention to these factors and you can probably find little safe spots in your yard that will let you grow those plants that you used to envy in your neighbor's yard.
About the Author
Carol is a garden writer and college professor in northeast Pennsylvania. She manages the Gardening section of Suite 101.com, where she also writes the column Virtually Gardening.