Natural environments evolve effortlessly, so why oh why do we have problem areas in our gardens? Everywhere else on earth, these areas are simply places for something different to colonize. By identifying different microclimates in our gardens, we can turn these challenging areas into assets. Even better, we can increase the range of plants that will grow in our yards.
What is a microclimate?
Those living in Northern California above the Bay Area are well aware of how a microclimate can change their gardening plans. However, no map can show the enormous variations within zones caused by topography, soil, vegetation, buildings, and any combination of such on a much smaller scale – a microscale.
Definitions vary, but a microclimate is a smaller area with its own unique climate within a general climate zone.
For example, microclimate creates different plant communities on the northern and southern sides of mountains, ridges, and valleys. A metropolitan area near the coast has few frost touches compared to the cooler, higher hills further inland. The hills also have different rainfall due to elevation and topographical effects on weather.
Microclimate exists on a smaller scale, too. My garden’s southerly aspect means soil warms more slowly in spring than in nearby gardens facing north. The area by the sunny northern brick wall of my house differs from the south-easterly slope under the loquat. Shrinking the scale further, the top of that slope is perfectly drained, the bottom soggy.
Why does microclimate matter?
Plants have different growing requirements – in soil texture, pH and drainage, in the amount of sunlight they like, in frost tolerance – and the simplest and best results always arise from matching those needs to the existing microclimate.
We already manipulate conditions in our yards by altering light with shade houses or temperature with glasshouses.
However, armed with a little more knowledge and an objective eye, gardeners can also maximize results by harnessing or tweaking rather than completely altering existing microclimates.
Gardeners in cooler climates may struggle with tropical plants, but they can almost always find a special spot for a few and more warm temperate ones. Subtropical gardeners can try tropical and warm climate plants, while lucky warm temperate zone gardeners can grow the widest range.
The easiest way to harness microclimate is to match plant needs to extremely site-specific conditions. In my garden, which is relatively frost-free warm temperate, plants that dislike heat, such as raspberries, thrive in areas protected from the afternoon sun.
Mediterranean plants like grapes, citrus, and figs grow in full sun, and subtropical plants, including lemon myrtle, macadamia, and finger lime, are in dappled shade, protected from both frost and summer heat. A nashi pear thrives in an area that’s too wet for most other fruit trees.
Microclimate results from complex interactions, but harnessing it is simplified when you consider the three main players: moisture, sunlight, and temperature.
Harnessing soil moisture and drainage
Where are the wettest and driest spots in your garden? All plants require more or less water, more or less frequently, whereas drainage determines how quickly water moves through the soil. Most plants prefer well-drained soil with water moving rapidly through root zones. Susceptible plants quickly succumb to root rot when moisture is stagnant or slow-moving.
Sandy soils are usually well-drained; clays drain more slowly, especially on flat ground or in hollows, so one of the most obvious tricks is to plant moisture lovers in swales (low or hollow places, especially a marshy depression between ridges) and those that prefer dry feet at or near the top of slopes.
Correctly matched to microclimate, many natives need little or no artificial irrigation once they are established. In Australia, where my parents live, northerly aspects usually have drier, shallower soil than southerly ones, and can be difficult to green in hot regions.
Dig generous planting holes, improve soil with organic matter, mulch well, and water seedlings regularly for the first season. Fruiting plants that survive dry soils once established include dates, olives, figs, quandongs, pomegranates, grapes, and pistachios (fruiting improves with irrigation).
In rainy gardens with clay, the best-drained sites occur at or near the tops of slopes, raised beds or rockeries, and in or atop retaining walls. Thyme, rosemary, and succulents, plus natives thrive in my dry stone retaining walls.
Two tiny caper bushes, loathing the rainy winters, have (barely) survived two years atop one wall – it’s still too wet, so I’ll replant between rocks where there are even less soil and moisture. Planting into pots is also an option.
Other plants prefer damper places. In swales, along creeks, in seepage areas often found at the base of retaining walls, or near septic soakage trenches: plant small trees and shrubs with restrained root systems – but not edible root crops!
When assessing your garden, remember to distinguish between wet and poorly drained areas. Bog plants, including cress, Vietnamese mint, and arrowleaf, are practically aquatic, whereas blueberries require consistent soil moisture but excellent drainage.
Harnessing moisture in the air
Many tropical plants wilt in dry climes with their lush leaves no matter how much you water them. Look for your garden’s steamiest spots: try humidity-loving species in the most sheltered area with the least air movement, and apply thick, spongy organic mulches.
Use overhead irrigation or micro-sprays at night. Erect shade cloth screens around young plants; use windbreaks. Fill pot saucers with gravel and water or grow adjacent to an existing pond.
Conversely, consider the driest, windiest spots. Most desert plants dislike summer humidity and wet winters, and many vegetables also succumb to fungal disease with too much shelter. Plant these in the best-ventilated areas and maximize airflow by increasing plant spacing.
Thin tree canopies and perimeter plantings, and choose wire fences instead of solid ones.
Mulch with gravel, pebbles, or non-absorbent materials such as pine bark, use drip rather than overhead irrigation, applied in the morning rather than the evening.
During cold, wet winters, potted plants susceptible to fungal disease often prefer a bright northerly porch where leaves and stems stay drier than in the open garden.
Harnessing sun and shade
Shade may be dappled under trees, solid beside buildings or structures, and also vary with time of day and season. Dappled shade also varies. Deciduous trees provide summer shade and winter sun, ideal for camellias, azaleas, herbaceous perennials, and fruiting plants such as red currants.
The evergreen shade is year-round. To increase light, selectively thin tree branches.
Solid shade south of fences and buildings varies with distance and season.
Is it shady year-round? If so, is it moist or dry? Some of the trickiest areas are completely shaded in winter but receive the afternoon sun in summer.
Try summer vegies or plants that tolerate a range of conditions (rhubarb, perpetual spinach, parsley). Choose hellebores that go dormant during the summer heat, or herbaceous sun lovers such as Jerusalem artichoke, autumn-flowering bulbs, and alstroemeria that die back in winter when it’s shady. Pot summer annuals such as petunias and transplant when the light reaches the ground in late spring.
In autumn, interplant winter annuals like pansies. Move pot plants to chase the sun. Taller trees and shrubs that are dormant in winter, such as apple, pomegranate, chestnut, medlar, or flowering cherries and plums, are another option – slow initially but eventually reaching the sunlight. For a faster effect, choose advanced trees.
Morning and afternoon sun makes a difference, too. The easterly sun is particularly good for veggies, stimulating more growth than the afternoon sun’s equivalent. In Australia’s intense light, easterly aspects with morning sun are often sufficient for many northern hemisphere plants. In my parents’ garden, raspberries, blueberries, and red currants all thrive in the morning sun only.
Harnessing heat and cold
The warmest areas are usually also the sunniest. In cold climates, try cold-sensitive plants such as passionfruit and citrus near heat sinks like northerly houses’ walls. Northerly aspects warm soonest, for longest. This is the place to try plants that are at the limits of your cooler climate or plants for which your growing season is a bit short.
Windbreaks warm these areas even further. Isolate-covered porches often suit cold-sensitive potted specimens; tree canopies also provide some protection to frost-tender plants.
The coolest parts of a garden are generally on the southeastern sides of houses, in the shade along the uphill side of solid fences, and in swales or closed valleys where cold air can’t drain away. Try plants for which your region is just a little too warm.
In hot regions, evergreen trees to the west and northwest provide afternoon protection for cooler-climate plants. Concrete water tanks also moderate temperature: try kiwi fruit or raspberries on the eastern side.
Harnessing microclimate for climbers
Look beyond the usual archways, trellises, and porches to fences, garages, posts, and chook runs – choose deciduous climbers such as grapes to give the girls plenty of winter sun. In cool regions, plant cold-sensitive climbers on the northern side of masonry walls.
In hot regions, plant beans, peas, and passionfruit to the northwest to protect veggies from the sun. In my garden, cloud forest passionfruit survives summer heat in permanent shade on a shed’s southeastern side.
Finally, if you’re unsure about a new plant’s needs, ask your local nursery for site-specific advice. And don’t be afraid to try different locations to discover that sweet spot: I moved some of my blueberries four times before finding their final home!
I’ve transplanted three-year-old macadamia to a shadier spot, a two-year-old avocado to a sunnier spot… and that finicky lychee is still in a pot because it may yet end up under the porch!
Apartments and Balconies
Apartment gardeners have limited space, but the same microclimate principles apply: do you have north, south, east, or west-facing balconies and windows shaded (or not) by trees or other buildings?
North or northeast balconies are warmest and sunniest, ideal for fruiting vegetables.
Easterly balconies in all but cold climates can usually produce leafy greens, whereas the shadiest and coolest south-southeasterly balconies suit ferns and other shade-lovers.
Northwesterly aspects in hot climates suit succulents and other tough plants. Microclimate also varies on the balcony itself.
On a traditional U-shaped, north-facing balcony, the coolest spot receiving morning sun only will be in the back corner towards the westernmost wall. The hottest place receiving sun for most of the day will be in the center close to the edge, while the side near the easternmost wall receives sun from the middle of the day onwards.
Move plants around and between balconies to meet seasonal changes. Find wheeled pot racks for ease of moving.
This article has been written by Linda McKerral for Prepper’s Will.
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