Microclimates Made Visible in Your Yard
Winter and spring keep crashing into each other as the seasons sort themselves out.
I’ve got a bit of everything – snow, ice, running water, mud, workable soil and dozens of early spring bulbs in bloom. Incredibly varied conditions – wet places and dry ones, sunny areas and shade, different soil depths, drainage patterns, exposure to sun and wind – are arranged in every possible combination in my half acre of actively gardened space.
What are Microclimates?
Microclimates are areas of slight climactic difference within a region. The urban heat effect, where brick, asphalt and concrete absorb the sun’s energy, makes cities hotter and drier than surrounding vegetated areas. Large bodies of water absorb and release heat slowly, creating a moderating effect at the shore.
High elevations are cooler than lower ones. Cold air drops, so deep valleys get early frost. South-facing slopes receive more sun, warming up earlier in spring than north-facing ones.
Orchardists use microclimates to advantage when they plant on slopes for good air drainage instead of in low-lying frost pockets, and avoid planting early-blooming varieties on warmer south-facing slopes, where frost threatens tender buds.
Microclimates in My Yard
We can take advantage of the microclimates in our own yards. My yard is very interesting right now – it’s not often that microclimates are so clearly visible. Where the snow disappears first is a big, welcome clue. The sun is higher in the sky now. A storm can dump a foot or more of snow, and it’s gone from my steep south-facing back gardens within a day or two.
Where does that much snow go so fast? I’ve been sternly corrected for saying snow evaporates; rather it sublimates – meaning it goes directly from a solid (snow and ice) to a gas (water vapor) without turning liquid in between.
The back slope is a really warm microclimate. It’s cupped and angled toward the sun, protected from the wind and well-drained, so that’s where intrepid early spring bulbs thrive, further encouraged by heat-retaining glacial boulders, stone walls, steps and stepping stones. I guess I could call it the rocky rural heat island effect.
Water and cold air flowing down the slope land at the back of my house. A small, two-story house casts a loooong shadow in winter. Extreme temperature fluctuations with sparse snow cover is hard on plants. Hellebores in the snowy shade by the house still have handsome green leaves, while the patch upslope are badly winterburned.
Better to freeze and stay frozen than to yo-yo through freeze-thaw cycles. Marginally hardy broadleafed evergreens like Skimmia japonica and sweet box (Sarcococca) are more likely to survive tucked into the ell of a house, untouched by winter sun.
March Flowers and Snow- All at Once
From my desk I’m looking across a 10’ wide swath of hard frozen snow. It thins out a bit then stops abruptly a couple feet from a stone retaining wall. At the wall’s base – clumps of snow crocus (C. tommasinianus), snowdrops (Galanthus nivalis) are blooming and early daffodils budded up and ready to bloom soon. Winter to spring in one gaze.
The crocus and snowdrops flowering now will be done by the time the clumps by the back door bloom. Planting the earliest and latest spots (and all the places in between) is a great way to extend the blooming season.
Conditions can differ greatly within very short distances, – and will change again when trees leaf out.
Well-drained Soil and Wet Soil
Larkspur seeds are best planted outdoors “as soon as the soil can be worked.” Last week I went out looking for a good spot and found it in the bed under my big juniper in front. The southeast side gets sun all day and the soil was perfect; the northwest side of the bed is still deep in snow. Plants that require well-drained soil will do better where the snow melts first.
Water that used to seep into the basement has been redirected to the soppy, partly shaded side yard. That’s where winterberries (Ilex verticillata), Clethera alnifolia, spicebush (Lindera benzoin) and witch hazels thrive. Poking through the snow, a carpet of winter aconites (Eranthus hyemalis) with frilly foliage and buttercup yellow blossoms offer a cheery promise of spring.