Microclimates in The Garden

By Richard Flowers, ACCNP-Green Thumb Nursery-Ventura

The two main types of climate zones that fellow gardeners may be aware are the UISDA Zones and Sunset Climate Zones. These zones tell you generally what plants may do best for a given area based on certain criteria. These climate zone indications can be useful in helping you determine which plant material may succeed in a wide geographical area however they are not 100% full proof and their are flaws. The USDA Climate Zones are very generic and is based on winter minimum temperatures and provides a useful plant hardiness index. It puts the Olympic Rain Forest in Washington state in the same zone as the Sonoran Desert. This is misleading because one area is a desert in southern Arizona and the other area is way up north thousands of miles away and is more coastal. The Sunset Climate zones are more precise which factors in summer highs, humidity, rainfall patterns, ocean influence, continental influence, elevation, and local terrain. How about if we take climate zones one step farther and narrow it down and make it more closer to home. Today I want to make you aware of another arsenal that you can rely on to make more precise determinations of what plant material may thrive in your particular piece of land – where you live, It is called microclimates. Most people do not take microclimates into consideration when gardening and they should.

What is a microclimate? Have you ever walked around your own garden and noticed a cold or warm draft in a particular area, what you have experienced is a microclimate. A microclimate is defined as the climate of a area that differs from that of the general surrounding region. The area can be as large as a city or as small as a plot of land; it may be measured in square miles or just a few square feet. A microclimate simply means that the climate, is different over here than it is over there. I will focus on microclimates in your own garden, a small plot of land.

Sometimes you could use a strategy to determine a particular microclimate by indicator plants. For example, if the Sunset Climate Zone or USDA Zone indicates that a certain plant will not grow there because it is the wrong zone and gets too much heat. But you experience that the particular plant thrives in the heat for many years, this is then an indicator plant that you can plant other heat loving plants despite what the “Zones” tell you. Another example would be if the Sunset Climate Zones or USDA Zones do not recommend a certain cherry for a particular area because it does not get cold enough but you have experienced that the cherry has flourished in the area for many years then you know that other cherries or similar fruits that require enough winter chill will thrive there despite what the “Zones” say.

In you own neighborhood have you ever wondered why the person across the street from you can grow a citrus successfully and you have trouble trying to get the fruit ripe? After all it is just across the street. Even in your own community there can be many microclimates. You might have various microclimates in your own yard. To choose the right plant for the right place, it is important to get to know your microclimates. Where I live, is a mostly banana belt, meaning a few blocks away during the winter time there will be frost on peoples plants, roofs and windshields, but where my house is there are areas where it is nothing of that nature but the are places in my landscape that it does occur. With that being said, there are many microclimates throughout ones community and even in ones own yard. That is why it is critical to understand and become familiar with the concept of microclimates in your own personal garden space. Applying the concept of microclimates and utilizing it to your own garden space should be taken seriously.

On just an acer of property I have about 20 microclimates. Some are seasonal while others others are permanent. I like to take full advantage of microclimates and filling them with a seemingly impossible array of diverse plants. The back garden ranges from cool and shady to a roasting south slope, with multiple zones in between. In my own garden I have landscape beds that are heavily mulched which insulates the soil by keeping it cooler during the summer and warmer during the winter for those plants that are tender to the cold. Mulch also reduces evaporation by as much as 50%. As the mulch breaks down it improves the soil structure, and improves drainage making the soil much easier to work with so plants grow better. The heavily mulched areas are on the north to east side which is cooler and more humid with Mediterranean to semi tropical types of plants. In contrast, I have garden beds where the soil is hard and un fertile. I have gravel or pebbles around plants like cactus and succulents to emulate a desert garden because these areas are on the southwest side of the property where it is a rain shadow, hot and dry, and the soil is poor. The front entrance is also hot, sunny, surrounded by a wall on two sides, and the house on the other creating a challenging microclimate that is a heat island. I made this area a southwestern feel with cactus and succulents in pots because the area is all cement. My own yard contains other small-scale heat islands. My driveway is black asphalt and I have concrete or gravel pathways that absorb heat during the day and emit it at night. Depending on the air movement, garden beds surrounding the said areas are warmer. I find it to be very essential to mulch these areas. My house is light colored with stucco walls this also radiates heat at night. A shrub hedge that tolerates heat and closeness to the house (Oleander hedge) is perfect there to hide the ugly wall and help cool the house.

The particular topography of my garden happens to be a gentle slope with clay soil. This affects the amount of solar radiation,  wind exposure, and water flow.  Cold pockets  often form at the bottom of the slope. The highest part is cooler in the summer but warmer in the winter. The lowest part of the slope is cooler in the winter but hotter in the summer. Water always drains to the lower point of the garden and for this reason its own unique microclimate exists there. This area is muddy and sometimes standing water after long periods of heavy rain and remains that way for several weeks. Ferns do best there. Other areas in my garden where the soil drains well and it is easier to dig due to prolonged use of mulch improving the soil for many years. Still other areas especially on the upper part of the garden the soil is hard and challenging to dig, the soil drains slower. Soil drainage varies from one spot to another. I dig test holes 1 foot deep and1 foot wide, fill with water, after a few hours in spot “A” it it is completely drained, in spot “B” in 15 minutes it is has no water left, and the next hole “C” I come back the next day and there is still water. Drainage in hole “ A” is good, drainage in hole “B” is excellent, and drainage in hole” C” is bad. This percolation test will dictate what kind of plant material one needs to use in a given area. I have learned from experience years ago that my citrus tree did not fare well because the soil is not fast draining, so I decided to use a more adaptable fruiting subject, so I went with Santa Rosa Plum. My Santa Rosa Plum is growing on a rootstock called Citation which is noted to do well in a poorly drained clay soil. Some areas in my landscape are fill dirt which drains better and is not as hard and compact.

When I am planting or planning on planting something I take into account how much sun or shade it may need. Since the plants are planted in rows then orienting the rows east to west will maximize the amount of sun that my trees will receive. Some areas in my landscape receive dappled or filtered shade, off and on, throughout the day. Canopy trees provide high dappled shade in the morning, some midday sun, and bright shade in the afternoon. This allows me to grow Lilly of the Nile , kaffir Lilly, and some ferns. The tree roots from the above trees are something to contend with as they do compete for water from the understory plants. The sun and shade exposures changes with the time of day and the season. Eastern exposure gets morning sun, less wind, and are typically moister while the west facing area gets the afternoon sun and is usually hotter, windier, and drier. The Northern direction is mainly shady much of the day and is cooler and moister. Southern exposures are warm and sunny even in winter. Thus, southern exposure gardens have longer growing seasons, and are warmer and drier. Some areas get full sun all day long ( 5 or more hours of sunlight a day). Summer sun is hotter, longer and higher in the sky, while winter sun is cooler, lower in the sky and shorter. Dense plant cover and mulch can also affect the microclimate, by helping to prevent water loss and cools the the soil.

I have lots of hanging plants. Knowing that hot air rises, hanging plants always dry out quicker than the same plant that is not hanging. My greenhouse for tropical plants creates a whole new microclimate. Other people may have a make shift shade house or overhang creating microclimate to harbor delicate plants from the adverse elements.

Temperature in the garden can vary from one place to another. As an example, I have an outdoor thermometer in the patio that reads one reading while another thermometer where the porch is reads a temperature that is three degrees different. Even though this differential in temperature is small but it is important. I have a number areas where the weather varies considerable enough where I need to move frost tender plants in the winter to a warm wall or cover such plants because these areas get cold drafts because they are in the wide open site on the north side where cold air settles, it is a cold pocket with no other protection. Using a simple covering such a a box or bucket with holes in it creates a microclimate to protect vulnerable plants from the freezing temperatures because the few degrees it warms the area makes all the difference. Likewise, even using a small umbrella to protect a few plants from the extreme hot sun, drying winds, and heat creates another microclimate. A warm wall provides several degrees warmer which can make a world of difference for tender tropical plants during the winter. A warm wall also provides another microclimate for plants like (Texas Sage) that enjoy the summer warmth where they thrive form the radiant heat the wall provides.

The hedge (Wax Leaf Privet) I use for privacy also helps to block wind from damaging tender plants. The shade cloth canopy covering delicate plants creates a microclimate that protects plants from damaging winds, hot sun, reduces water evaporation, and cools the area. Tall trees or shrubs can do the same thing. When large trees are pruned, opening up the canopy to help more light beam though so plants grow better creates yet another microclimate. On the flip side, if the large trees were over pruned or removed entirely more sunlight enters the area that could result in damaging existing plants. I have areas that have young trees and shrubs that do not take up a lot of room but when they grow to their mature size the area where they are the dynamics will change causing more shade, cooler, less evaporation, and less wind.  Another area that is often overlooked is where the dryer vent is or the air conditioning unit is situated.
The hot drying air can have a negative result in plant growth. No plantings are near such an area.

Inside the house, for house plants, areas next to a south window are incredibly hotter and the sun that beams through the window act like a magnifying glass which can burn plant tissue. The farther you go away form the window, the less light intensity it gets which also affects the plant growth. If I close the shades, the temperature is reduced and light is limited also has a reaction to plant growth and changing the climate in that area.

With all that being said, some areas in the garden with the same exact plant may grow, bloom or fruit later or earlier in different areas of the garden due to varying microclimatic conditions. By being aware of microclimates in your garden you will discover it plays a very important role in selecting plant material, care, watering, placement, and the overall health and vigor of the entire garden. Knowing this concept will make you become more in tune with your own garden so your have a better understanding how to make your plants thrive. Knowledge gained form your own particular microclimates can make a world of difference in selecting and placement of fruit trees, plants that need pronounced heat, or winter chill to grow, set flowers, and fruit.

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