Microclimate

Each landscape is unique. Even within the same zip code, there can be many different microclimates that feature a variety of slopes, exposures, and soil types. Very often, the same yard can have several different microclimates.

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Note to my southern hemisphere readers: all the directional comments in this post are egocentrically oriented toward the northern hemisphere. My apologies.

Microclimates are the localized conditions of temperature, moisture, sunlight, wind, soil, drainage patterns, and other factors that make one site more suitable to some plants than others. While some areas get more rain, others may be in wind-blocking pockets that are more prone to fungal disease, as others face the ravages of heavy traffic or scorching summer heat. The local news channel may never get your yard’s weather correct. But don’t let that stop you from learning more about the microclimates in your landscape. The more time you spend learning about your yard, the better you are able to judge what will work and what won’t.
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For example, Silicon Valley is in plant hardiness zone 9b and it averages 17” of rainfall each year. The first and last frost dates are November 15 and March 15, respectively. The soil is a heavy, alkaline clay, which tends to get compacted into a material similar to concrete. The tap (irrigation) water also tends to be alkaline. These factors make growing acid-loving plants, such as blueberries, more difficult, but not impossible.

By figuring out the microclimates in your landscape, you can select and manage plants much better than by winging it with what looks good in a catalog or on a store shelf. Simply guessing about or ignoring these factors can mean increased pest and disease problems, more water consumption (and waste) and unproductive plants.

Map your yard

This may sound daunting, but modern technology makes it relatively painless. If you prefer, a rough sketch will also work. To create an accurate map of your landscape, use these steps:

1. Find a satellite image of your property.
2. Take a screenshot.
3. Print it, using the higher quality settings.
4. Use tracing paper to trace over the  property lines and all of the anchor points.
5. You now have a map of your landscape.
6. Scan this image into your computer and print a few copies.

Scanned satellite image of yard

Tracing of satellite image of yard

This map will prove invaluable as you sort out your landscape’s microclimates and determine where plants will suffer or thrive. You can use color coding to document the various factors related to microclimate, or put each factor on a different sheet. It doesn’t matter, just do what works for you. [Or you can contact me for this handy landscape service!] Just be sure to update your landscape map as new trees and other large features are added.

But, before you start planting, you need to know your hardiness zone.

Hardiness Zones

The first step in identifying microclimate is to determine your Hardiness Zone. A hardiness zone is a geographical region sorted by the lowest annual temperature. Recent scientific research has caused some changes to this map, so double-check yours. Simply find your location on the map above or use the USDA’s interactive map and note the number-letter combination on your landscape map. Use your Hardiness Zone to help you select plants best suited to your region. Next, take a look at sun exposure.

Sunlight and direction

How much sunlight a plant gets, and when it receives that sunlight, can have a huge impact on plant health. Without enough sunlight, plants die. You see words like “partial shade” or “full sun” on seed packets and plant labels, but what do those words actually mean? Here’s your answer:

• Full sun means 8 or more hours of direct sunlight every day
• Partial sun means 4 to 6 hours of sunlight in the afternoon
• Partial shade means 4 hours of morning sun
• Shade means bright dappled sun all day or 2 hours of direct morning sun

One easy way to learn about sun exposure in your yard is to use your camera. Every few hours, take several photos of your property. This will show you sunlight exposure patterns, along with wind and dead air pocket trends, and problems you may not have suspected (such as a pesky squirrel).

It is a good idea to do this in June and again in December, to get an a sense of the seasonal changes. You may be surprised to see how trees create shady areas that feel wonderful in summer, but deprive sun-loving plants of the sunlight they need at other times of the year.  Keep in mind, as trees grow, those sunlight exposures will change.

Which direction does your garden face?

When you head out to your garden, which cardinal direction are you facing? Is there a large tree that blocks afternoon sun in the west, or a northerly fence that slows evaporation? Generally speaking, north and east facing areas are cooler and more moist, while southern and western areas are sunnier and drier, though not always. Each cardinal direction has characteristics that impact your plants:

• Northern exposures receive the least sunlight, are more moist in summer, and tend to receive more frost and snow in winter, creating a shorter growing season.
• Southern exposures are warmer, tend to dry out earlier, and are more likely to provide full sun.
• Eastern exposures are cooler and more moist, receive more morning sun, and are best suited for plants that love partial shade. These areas also tend to have less wind problems.
• Western exposures mean lots of afternoon heat - the perfect location for peppers and other heat-loving plants. Westward exposures tend to receive the most wind, as well, and usually receive partial sun.

Ask for help

Next, contact your County Extension Office to learn your local frost dates. Keep in mind that these dates are statistical averages - your yard may be somewhat different. This information is important for protecting frost sensitive annuals and perennials, as well as in fruit and nut tree selection. Many trees will not produce fruit unless they receive a minimum number of chill hours.

Heat sinks, frost pockets, and anchors

Structures, paths, walls, and fences absorb the sun’s heat during the day and release it at night. You can use these heat sinks to your plants’ advantage, helping them through a cold, dark winter night. Just the opposite, low-lying, northern facing areas can create pockets of cold, damp air that make life difficult for plants. These are the areas where frost first appears.

Anchors, such as large perennial plants, structures, hedges, fences and walls all impact light and rain exposure:

• Eaves may provide protection from frost, but they can also redirect rainfall away from plants.
• Hedges, walls, and fences can create swirling winds and shadows, or may provide wind protection.
• Structures can cast shadows, create wind barriers, and retain heat. Heat retention determines how much heat is collected.
• Trees create shade, may provide wind protection, and often reduce the amount of surface water available to nearby plants.

Frost pockets tend to occur in low areas behind northern facing structures. If you haven’t already, note these heat sinks, frost pockets, and anchor structures on your landscape map.

Soil composition

Soil is the bedrock of your landscape. Without healthy soil, you cannot have healthy plants. Unhealthy plants attract pests, succumb to disease, and generally create more work than they are worth. If you do nothing else for your garden, get your soil tested by a reputable lab. Soil structure can be sand, silt, or clay. Each has distinct characteristics that have huge impact on your plants. Clay retains more nutrients and moisture than sand, but it is more likely to be compacted. Get your soil tested and mulch everything that isn’t planted with a 4” layer of free arborist chips from your local tree trimmer. You’ll be glad you did.

While you are at it, conduct a perc test to see how good your soil’s permeability is. Poor drainage can kill plants.

Keep in mind, many of these factors are not written in stone. A northern-facing corner of the yard surrounded by trees does not necessarily have to result in dampness and drainage problems. You can always prune those trees to allow for more sun exposure and improved air flow.

Once you have a better idea of the microclimates in your landscape, you can group plants with similar sunlight and irrigation needs.