In the Garden:
New England
March, 2004
Regional Report

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Provide a spot sheltered from winter winds and your rhodies will reward you.

Maximizing Microclimates

The annual spring tease is upon us. One week we're shedding jackets and pruning branches off the crabapple trees, the next we're driven back inside by threatening snow. Spring is a long time coming in New England, but this gradual warming does have at least one advantage: it gives us a chance to learn more about the different microclimates in our landscapes.

No matter what zone you live in, there are climatic variations between different parts of your property. By noting these different "micro" climates, you can locate plants in the most suitable spots, and even broaden your choices of plants.

Extending the Bloom Time
Obviously the north side of your house gets less sun than the south side so there are different microclimates in those two areas. But even a large rock, a fence, a stone wall, a patio, large trees, or a slope can create a unique microclimate. Next to the south side of my house the daffodils are peeking up. But other locations are still under a snowy blanket. This is good news: it means I can have a longer season of flowers. When the flower bulbs next to the house are fading, the ones partially shaded by a big boulder are just opening.

Pushing the Zones
Aside from prolonging the bulb show, taking advantage of different microclimates can enable you to grow plants that are borderline hardy in your region. My stone walkway and patio absorb heat and allow me to grow plants nearby that are usually only hardy to a zone warmer than my zone 4. I've even had zone 6 plants survive winters there; not routinely, but I'll happily take what I can get.

Locating Frost-Sensitive Plants
Those last patches of melting snow in spring are also good future sites for trees and shrubs that are sensitive to late spring frosts, such as magnolia and peach trees. Cold damage is most likely to occur when these plants are located in warm spots, such as near a structure that radiates heat from the sun. The trees get the message that spring has arrived and it's time to start growing. Then the tender new shoots and flower buds are likely to be killed by those inevitable late frosts. If you plant frost-sensitive trees and shrubs in those cold spots indicated by late-melting snow, however, they will be slower to put out new growth and thus have a better chance of thriving.

Getting Out of the Wind
Wind also influences the microclimates in your yard, both by lowering air temperature and by increasing water loss through the foliage (transpiration). Some plants, such as rhododendrons and other broad-leaved evergreens, are especially damaged by cold winter winds, because evergreens don't go completely dormant and thus lose some water all winter long. Nestle these plants where larger trees and shrubs or buildings will provide a windbreak.

One of the most stressful locations for an evergreen is at the corner of a house because the wind can accelerate as it whips around the corner. Yet you frequently see evergreens standing as corner sentinels.

Another touchy location for wind- and cold-sensitive plants is along a solid fence that's meant to provide shelter from the wind. By totally blocking the wind, the fence creates back currents on the downwind side that can actually increase the wind damage to plants. If you want a fence to protect plants from the wind, use a semi-open fence – like a slatted snow fence – that allows some air to pass through but deflects the brunt of the wind.

Slope Effects
Slopes also offer different microclimates. You'll notice your south-facing slope warming up sooner in spring, so that's a good spot for an annual garden because you can plant sooner. But trees on this slope may need their trunks wrapped in winter to protect from sunscald caused by dramatic temperature swings from day to night. North-facing slopes, which are slower to warm up, would be the place for trees sensitive to spring frosts because they'll emerge from dormancy after frost danger has passed.

Now I'm looking at my new stone retaining wall next to my vegetable garden and thinking, hmm, how many zones can I push alongside that wall? OK, mangoes might be wishful thinking ...


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