If you garden indoors, you already know that creating the right growing environment produces healthier plants. Think of indoor gardening as a premier, man-made microclimate, a limited area within a larger locale where somewhat different atmospheric conditions are in effect.
You’re familiar with the idea of controlling the growing environment for indoor plants, but when you move seedlings outdoors, some of that control vanishes, right? Well, maybe less than you think. By understanding the microclimates in your landscape, you can customize your planting strategies, and maybe even broaden your planting options.
What’s a Microclimate?
You already perform a little microclimate analysis in the garden. You know the areas of your landscape that get the most shade, for instance. A microclimate is a location where the prevailing climatic conditions vary slightly from the norm. This can be the result of one or a number of environmental factors.
For example, old-school growers pay close attention to spots where frost and snow linger longest. It’s a useful way to recognize areas most susceptible to early frost or lower-than-normal overnight temperatures. Both low-lying and shady areas in the garden can be microclimates because the environmental conditions in these locations are consistently different from those in the garden as a whole.
Temperature and Microclimates
Frost-prone and shady areas aren’t the only temperature-related microclimates. For instance, urban locations tend to be somewhat warmer than their suburban counterparts because concrete and asphalt absorb heat during the day and release it during the overnight hours, while areas near lakes and rivers may experience slightly cooler temperatures, especially when there’s a breeze coming off the water.
The US Department of Agriculture’s Plant Hardiness Zone chart helps many gardeners decide which plant varieties to grow. It is so helpful, many seed manufacturers print zone guidelines right on their packaging. Even though they are a common and useful tool, hardiness zones may be a bit deceptive.
Geographical zones are based on their average annual low temperatures, which are calculated using 30 years’ worth of weather data (from 1976-2005). The numbers go from coldest (1) to hottest (10), and a difference of 10°F distinguishes one zone from the next number up or down.
This means the average annual low temperature for Zone 6, for example, is 10°F cooler than the average annual low temperature for Zone 7, and 10°F warmer than what can be expected in Zone 5. Although you may not see it on seed packets, the USDA’s zone designations are further broken into 5°F divisions. Using our Zone 6 example, 6a is 5°F cooler than 6b and 5°F warmer than 5b.
Since just five degrees can separate one zone from the next, temperature fluctuations in your garden may compensate for that shortfall. Re-evaluating your real estate based on its microclimates can throw parts of your garden into a new zone, and also into a whole new world of planting possibilities.
Hardiness Zone Game Changers
Buildings and hardscapes like driveways, patios and fences tend to make adjacent areas warmer overnight. The effect is enhanced if a building or hardscape element also acts as a natural windbreak and you’ve planted along the protected side. Color can play a role, too. White walls or fences reflect light and heat during the day, while darker colors tend to absorb heat and release it as the temperature drops.
On the flip side, elevated spaces like decks and patios can be colder than normal, particularly when it’s windy. Low-lying areas in the garden can also be colder than expected. Cold air is heavier than the warmer air aloft and tends to pool in depressions and downslope locations.
Although temperature can be an important factor in microclimate analysis, it isn’t the only consideration. Microclimates can be large or small, and can include elements working alone or in combination to modify the prevailing conditions in portions of the garden. Let’s look at the most important factors to consider when identifying a microclimate:
- Urban development – Proximity to large buildings, roadways and other urban features that retain heat can increase the ambient temperature.
- Proximity to water – Lakes can effect some major cooling and less-pronounced cooling can occur when breezes transit rivers, streams and large ponds.
- Heat-retentive features – Hardscapes like driveways, walls, fences, decks and patios tend to make adjacent areas warmer overnight.
- Windbreaks – Sheltered locations somewhat protected from damaging wind and driving rain are more temperate than the surrounding terrain.
- Orientation – The direction your property faces, based on the points of the compass, impacts temperature.
- Shade-producing features – Buildings and trees can create pools or bands of shade relative to their directional orientation.
- Topography – The surface features of your property, like depressions where water pools and frost lingers, or hilly areas that are vulnerable to windy conditions or moisture loss during hot weather, can create microclimates.
- Soil conditions – The soil composition in different parts of the garden, like mulch that provides insulation, or compacted soil that retains heat, impacts temperature.
A good understanding of a garden’s microclimates can be a powerful tool. Think of yourself as a real estate agent with a botanical bent. What’s the first rule of real estate? Location, location, location! Your challenge is to first identify the microclimates in your landscape, and then pair them with plants that can capitalize on their unique benefits.
Your house is probably one of the largest shade-producing objects in your garden. At different times of the year it casts a larger, smaller, stronger or weaker shadow based on its directional orientation and the sun’s elevation through the seasons. Understanding where and when that shadow will hit can be a valuable tool in maximizing—or minimizing—the sun’s impact on your plants. Using shade creatively can be a subtle but important stratagem. For example, morning light and afternoon shade may help keep cilantro and dill from bolting as quickly, and could make it easier to maintain lettuces and spinach outdoors in summer.
That wet, somewhat boggy spot around your downspout may not be the best place for lavender, but it could be perfect for mint, especially if you provide better drainage with soil amendments. That hot, dry area near your garage, the one that gets bright afternoon light and plenty of reflected heat from your concrete driveway, may be a terrible home for lawn grass, but could be the best location on your lot for globe amaranth or cosmos.
You might already realize the south-facing hill behind your house is hot, dry and not very plant friendly. Other areas of your garden can be harder to evaluate, though. There are a number of tests you can perform to analyze the temperature extremes, available sunlight and soil conditions in different sections of your property. You’ll get useful results right away from soil and sunlight tests, but the big bonanza comes from evaluating your garden through a number of seasons to get a complete microclimate profile. This involves weekly testing and some record keeping, but it’s worth it.
The first step is to choose sections of the garden to evaluate. This can be as easy as treating your front, side and back yards as independent locations, or exploring elevated, windward or low-lying areas separately. Based on the information above, you probably already know which spaces you want to look at individually.
Even though you can get a lot of information by being observant and taking the time to position and reposition a simple thermometer around your landscape to track temperature variations, there are tools that can make the testing phase of microclimate analysis easier and more productive. They include:
- Outdoor thermometers
- Soil test kits and meters
- Moisture meters
- Sun gauges
- Wind gauges
Multitasking tools that can gather more than one type of information are available, too. One is a weather station that can track weather conditions from multiple probes positioned around your garden. The data is transferred to indoor equipment wirelessly, eliminating the need for manual testing in inclement weather or during the late-night hours. Although data tracking features will vary based on the manufacturer and model you choose, some weather stations will monitor temperature, wind speed and direction, rainfall and humidity.
It’s pretty easy to see that a few small variations can produce a microclimate. In fact, you’ve likely created microclimates using old standbys like cold frames, row covers and raised beds. The idea of building a whole new microclimate may have occurred to you, too. Once you understand what’s really going on in the garden, you can use your current microclimates creatively, and even build new ones.
Microclimates offer enhanced variety in the garden, and understanding them can help you avoid planting mistakes that result in unnecessary losses. What you learn will even answer lingering questions you may have about why some plants thrive in your landscape and others don’t. Armed with good information, you can start to grow a better garden outdoors, just the way you grow great seedlings indoors.