Or Why Your Neighbor’s Tomatoes Ripen So Fast!
Do you ever wonder why plants in one place flower and fruit so much faster than others planted nearby? And this happens repeatedly? It’s all about the microclimates, little places that operate all on their own. You can study hardiness zones, heat maps, and botany but if you don’t figure out the microclimates in your garden you might be risking it all.
Our microclimates influence ecological processes such as:
- Plant Regeneration: The microclimates affect the photosynthesis process and plant growth,
- Soil Respiration: indicates how the soil converts nutrients in organic matter in a form the plants can use. Soil Respiration USDA (This is a PDF you can download.)
- Wildlife Habitat: Temperature changes can affect food sources, vegetation, access to water, and other factors. This can cause animals to migrate or species even to die off.
In your garden, it is the climate that influences growing conditions. This includes air and soil temperature, precipitation, and heat accumulation. Some days in the garden we think we can’t live with our climate but the truth is that we can’t live without it!
Microclimates: How To Identify Them
If a climate is a ‘measure of the average variation in overall weather patterns over time and over a wide geographic zone’. (WSU Extension Service, see resources at the end.) Then a microclimate is a relatively small space where conditions will differ, noticeably and consistently, from the surrounding climate zone. And they will differ enough so that our planting and care decisions are affected!
Examples Of Microclimates You May Know
San Francisco is influenced by urban heat islands, a layer of marine air, and famously varied topography. Walking in the city you can experience a 9-degree F. variation from one city block to another!
Switzerland is a country famous for its snowy mountains but it contains a region called Ticino. It has a microclimate so mild that while famous for wine grapes it also grows palms and bananas!
Why Do We Care About Microclimates?
We gardeners all study our plant hardiness zones, to know if cold will kill our perennial plants and we are learning to work with heat zones to help with the opposite problem; heatstroke for our plants. But those factors are convenient guidelines for the garden, they are not rules. If we understand the microclimates that define our individual, gardens we are going to get important benefits.
- We will do better at putting ‘the right plant in the right place.’
- We will take fewer risks with valuable plants in times of temperature extremes.
- We may find ourselves able to grow desirable plants in places beyond their expected zones because we found a little microclimate that suits their needs.
What Influences Microclimates?
Never overlook these important elements:
- Topography
- Elevation
- Slope
- Exposure
- Soil Composition
- Proximity to mountains and hills
- The predominant wind
- Large water bodies
How Big Is A Microclimate
As a microclimate is a significant difference from the larger climate zone around it, you will find that it can vary greatly. A microclimate that influences what and how we plant can be as small as the south side of a house or even a wall or as big as a whole valley.
The Encyclopedia of Ecology tells us that microclimates vary according to the kind of question you are asking. So, for example, a landscape ecologist may be studying a desert area that is hundreds of miles in length. But a reproductive ecologist interested in a certain bug will consider a microclimate to be the inside of a single plant!
And our interest as gardeners is the differences we find in various parts of our gardens. We need to address microclimates from our viewpoint.
What Specifically Is Significant About Microclimates?
A microclimate influences ecological processes. These include:
- Plant regeneration
- Soil respiration
- Wildlife habitat
The Five Things That Influence Microclimates
- Air Temperature: Air is heated by the sun but also by surfaces that are, themselves, heated by the sun. This means that air at different levels in the same place can vary. A cold sink makes the air near the ground colder than it feels above.
- Wind Speed: A strong wind usually cools us and the plants around us. We can feel this effect.
- Humidity: Evaporation can’t take place if the air is full of saturated moisture. In a humid environment, we feel hot; it is easier to cool down in dry air. The plants experience what we experience.
- Solar Radiation: You feel the temperature when you move from sun to shade.
- Complexity: All these features influence each other and change over time.
The Best Ways To Identify Your Specific Microclimate
Check Your Garden Temperature
Using your outdoor thermometer, check the temperature on a regular schedule, and record it. Identify the range over time. Compare your garden temperature averages with the average temperature for your zone. Is it different? You have identified a microclimate!
Compare What You Are Learning To Your Plant Hardiness Zone
In the United States, we have been measuring and using hardiness zones based on authoritative data, since at least 1927. By now this information is universally accepted as a valuable guideline for gardening. Look at the labels on the plants in your garden center; read any online catalog; you can find hardiness zones everywhere.
They have other virtues, the plant recommendations come from many years of plant trials, and other parts of the world are making their own versions of hardiness zones.
The Limitations Of Plant Hardiness Zones
Once you fully understand the quirks and benefits of your own garden microclimate you begin to appreciate the limitations of zones. They are averages, they are not guarantees of how cold or hot it can get, and they do not reflect your garden. And they won’t buy you new plants if yours dies in a weather surprise!
How To Evaluate Your Garden’s Microclimates
Know These Things First
- Your plant hardiness zone
- Your actual coldest winter temperature
- Your growing season
- Sun/shade map of your garden
Important Features To Evaluate
This is an excellent piece called “How to Assess Your Microclimates” written by the University of California Master Gardeners in Marin County. It also comes with a helpful form to use in evaluating your garden. I think you will like it and you can download the form. The West Coast is legendary for its extremes of microclimates and UC devotes time and expertise to understanding them.
How To Find Warmer Microclimates
This exercise requires getting up early and going outdoors on a frosty morning. When you expect frost tonight, set your alarm for dawn. Get out as soon as it is light enough to see but before the sun removes some frost. Look through the shiny silver frost areas for places without frost. They may look brown and damp, but these are your warmest microclimates. Look for these along walls, buildings, and fences. They may be only a few feet in diameter but you can use these to plant marginal trees, shrubs, or plants.
Identify Your South Facing Walls
These spots are so highly likely to be warmer microclimates that they should not be overlooked. You may well have identified a half-hardiness zone or a place about 5 degrees F. higher than the greater garden.
The Hot Wall: Creative Microclimates
This is the walled garden at Croome Court, parts of it are heated on the inside to raise espaliered fruit!
By the 18th Century, the English walled garden was a uniquely creative way to manage the garden’s microclimate. The wall itself controlled the climate, the garden was sheltered and sunny and the walls were a perfect place for climbing plants, However in 1718 someone thought up the ‘hot wall.’ If you like a good fireplace, so do the plants.
How The ‘Hot Wall’ Was Heated
The interior of the hot wall was heated by a fire in an oven, the wall was heated by hot air traveling through horizontal flues, and the air would escape through holes in the top of the wall. Along the wall, delicate fruits were grown as espaliered trees. These became very common but sadly few are left for us to see.
You can visit these, they are open to the public:
Croome Court: This today is the largest walled garden in Europe and you can visit it. It covers seven acres and includes the hot wall. The Palladian house, Capability Brown designed landscape. and the walled garden is located in Southern Worcestershire UK.
Chilton Foliat: This contains two walled gardens.
Topography
The forms and features of the land surface make up the topography of the garden. Topographic features include elevation, and the orientation of any slopes can influence your microclimate. Higher elevations are cooler, the orientation of the slopes will affect your exposure to sunlight and temperature, and very high places can affect wind patterns and rain.
Elevation
Your elevation affects the temperature in your garden. The average temperature will decline by 3-5 degrees F. for every 1000 feet in elevation. This is true even in areas near the equator.
Slope
A slope will influence sun, wind, and water flow. Look for cold spots at the bottom of the slopes. This is because cold air is denser than warm, it sinks to the surface and collects like water. Slopes can be difficult to impossible to plant on depending on how extreme. Below, you will find an example of a uniquely clever use of terraced slopes.
Exposure
Here are some useful notes on the direction of exposure.
North: Northern light is indirect as it is always in shadow. Northern light is diffuse and does not create glare. (This is why artists prefer it.) Your northern exposure garden will be shadier, and cooler and it will hold moisture.
South: In the Northern Hemisphere, a southern exposure is warm, sunny, dry, and has the longest growing season. It is the light condition we call full sun.
East: An east-facing garden has a more gentle morning light and avoids the harsh light of the afternoon. It will have less wind and will be more moist. This is partial sun.
West: The west-facing garden enjoys several hours of sunlight, however, they are the hours of the harshest afternoon light. It will be hot, windy and dry. Use plants that perform in harsh light.
Soil Composition
Soil affects the garden’s microclimate, it affects temperature and humidity by how quickly it releases or maintains water. Plant cover itself affects climate as it prevents the loss of heat or moisture from the soil. Look for these features:
- Does water evaporate or pool in place?
- Where does water sit?
Proximity To Mountains And Hills
On the windward side of a mountain, the air is cool and rain falls, the leeward side is warmer and dry. A garden in a mountain area will have cooler temperatures and shorter seasons than those below Look for spaces with 6-8 hours of sun, south-facing, and with a moderate slope. (If your garden is steeply sloped read the section on Upton House below.
Plants growing at high elevations must deal with these seven issues:
- Low temperature
- Strong sunlight
- Low oxygen
- High rainfall
- Lower nutrition
- Snowpacks that last
- Wind
Here is a list of plants to use in high elevations.
The Predominant Wind
Low wind speeds (below 5 mph) have a beneficial impact on growing plants, creating stronger branches and stems. High wind speeds, however, will strip leaves, break stems and even uproot plants. This may leave plants susceptible to pests and diseases and will exacerbate the effects of temperature extremes. Winds above 30 mph are the most damaging.
Large Water Bodies
Bodies of Water influence the temperature and humidity of your garden. Water loses and gains heat more slowly than land. This adds moisture to the air and increases humidity. Also, this has the effect of regulating extremes of temperature.
The existence of a large water body alone can create a microclimate. A body of water adds value to your garden because it limits the extremes of temperature.
How To Influence Your Garden’s Microclimates
Once you have identified the climate of the garden, you can affect your climate by taking some of these steps.
- To add warmth to north-facing garden beds; use hardscapes, including walls, patios, and rocks this will retain heat during the day and slowly release it at night.
- Make windscreens from hedges, groups of trees, and walls. We do not stop the wind effect, but we can limit its damage. In windy areas allow openings in the barriers.
- Use large living shrubs to create a windbreak.
- Shade trees and structures can protect south and west-facing and cool-season plants from strong sun.
- Use taller, sun-loving plants to protect cool-season crops.
- Consider covered structures for both heat and cold extremes. For shade, pergolas, arbors, and shade houses will help. Greenhouses, polytunnels, and storm coverings are also helpful in clod weather.
- Build windbreaks from trellises, tall planters, and other materials.
- Add shade for midday heat with vining and climbing crops
- Create warmth in low, cold areas by raising crops in raised beds.
- Plant on the south side of a structure (your house or outbuildings) to shelter plants from cold winds. This will block cold winds and the buildings will hold and radiate heat.
- Create more planting space on hillsides by using terracing.
- A small log placed at the base of the sunny side of the bed will keep the base of plants cool.
- Cover wet and cold planting beds with plastic before planting. The sun will warm and dry the soil.
How To Use Your Garden’s Microclimates
Plant Selection
Start with plants and varieties that grow easily in your garden and are recommended for your hardiness zone.
Use plants that are successful in the various orientations of your garden.’
North: A north-facing garden can appear dark and unwelcoming. Try to include variegated foliage with white or yellow as white or light-colored flowers.
Plants that do well in cool, north-facing gardens include these:
Huchera (coral bells), liriope muscari (big blue lilyturf), Polystichum (shield fern), Crytomium Falcatum (Japanese Holly Fern), Hedra Helix (common ivy), Dryopteris (Wood Fern), Skimmia japonica, compact shrub, Hosta, Impatiens, leafy vegetables, Hosta, Foxgloves, Iris.
Check your plant hardiness zones and keep an open mind about plants. Hostas are recommended for zones 3-9. However, a new hosta has been developed for Florida use. The sun hosta, in variegated green and white grows beautifully in our Zone 10 garden.
South: Gardens that face south, are warm and sunny. Consider plants like these, iris, lilies, salvia, verbena, and echinacea. Honeysuckle, clemantis, wisteria, and any sun-loving vegetables will thrive. The pictured vine is not wisteria, but queen’s wreath, a plant native to the Caribbean.
East: Plants that perform well in the morning sun of east-facing gardens include astilbe, hostas, bleeding hearts, ferns, and anemones. East-facing gardens tend to be moist, be alert for root rot.
West: Gardens that are west-facing are the second sunniest gardens. The afternoon sun while only available for half the day is extremely hot. Choose full and part sun plants. Daylilies will perform brilliantly in this environment, also, black-eyed Susan, coneflower, phlox, and hibiscus (both hardy and tropical). Also consider, salvia, sedum and yarrrow.
Effective Use Of Slopes
It is important to understand and value the effects of heat, wind, and light on sloping garden spaces, but one of the great gardening challenges is making productive use of extreme slopes. We visited this garden, Upton House, in Warwickshire UK and the remarkable steep slope was tamed beautifully. Have a look at this topography. (Upton House is near Banbury, not far from Oxford, the house has a wonderful art collection and the garden is quite a surprise!
Plan For Change As Your Garden Grows
Growing things is the pleasure of gardening and with growth comes change. Small wind and shade plants grow larger, light conditions change and your garden needs to adapt. Our current garden began with sun and turf. As we added trees, shrubbery and planting beds sunny places developed shade, and turf in some places failed. We developed a seating area with walkways and ground cover.
This is the story of the project:
‘How to Find a Low Maintenance Ground Cover That Rabbits Won’t Love’
Summary,
As gardeners, we have several tools to help us make decisions for our gardens, hardiness zones, heat zones, and botanical knowledge but gardening is like real estate or politics, the important parts are local!
This means that the most important knowledge is all about our own climates and especially the most important parts; those tiny microclimates of our gardens. If we know the place where we are making a garden we will succeed. It”s the little microclimates we dig that shovel into, that will make the most difference to our success.
Happy digging and remember what Cicero Said:
Resources You Can Use
‘How to Use The New USDA Plant Hardiness Zone Map’
‘How to Find Your USDA Plant Hardiness Zones For Florida
‘Some Like It Hot: Measure Heat In The Garden’
How To Determine Your Garden’s Microclimates‘ by Washington State University Extension Service. A PDF you can download it contains information and helpful diagrams.