A game of inches

Although I garden in Climate Zone 5B here in eastern Massachusetts, I got a reminder this week that conditions vary in different areas of my yard. The first frost brought an opportunity to observe small differences in temperature between areas as close as inches apart.

            Two pots of wax begonias (Begonia x benariensis ‘Big Red’) next to the front steps offered a striking demonstration of a microclimate, a small area with climate conditions different from its surroundings. The leaves on stems closest to the house stayed green when the night temperature dipped below freezing.

Frost blackened the leaves on stems just inches away on the other side of the large pots. The leaves that died were farther from the warmth radiated by the house’s foundation. 

Before the frost

Leaves farther from the house blackened and melted in the frost

I inadvertently demonstrated another source of radiant heat by leaving a full watering can next to one of the pots. It too absorbed heat during the day and radiated it at night, protecting nearby foliage from frost kill.

The water in the watering can protected the leaves on the left

            My first introduction to microclimates in my garden came when I planted maidenhair fern (Adiantum pedatum). Of three ferns I planted, two dwindled and died and one flourished prodigiously. It’s still with me twenty years later and has gradually produced a small colony. Apparently I’d been lucky enough to plant it in just the right place, on the eastern side of a tall white pine (Pinus strobus) and shaded from western sun by a yew (Taxus x media) and some hulking Catawba rhododendrons (Rhododendron catawbiense) inherited from previous owners.

Maidenhair fern colony in May

            I can’t claim credit for the fern’s success. It was only by chance that I planted it where I did. I can guess that it’s enjoying the right amount of water gently delivered as the pine catches rain on its needles. I knew maidenhair fern was a shade lover—that’s why I bought it. It must also like being out of the wind, sheltered from our prevailing west winds by the shrubs, but with less turbulence than a solid fence or wall would cause.

            The fern colony sits on a gentle slope that runs from the base of the pine to the lawn to its east. That must allow cold air to flow past it to the lawn a few inches below (interesting to know that cold air drains downhill, like water). The ferns are growing under a deep insulating blanket of pine needles and deciduous leaf mulch, which keeps soil moisture and temperature relatively steady.

This week the ferns are enjoying a fresh layer of pine needles

            It’s testament to the breeders’ art that the wax begonias bloomed consistently from May until late October. Unlike the maidenhair fern, they were flexible about accepting the hotter, drier conditions I provided. Now I’ll see if I can root one of the stems indoors and keep it going in yet another microclimate, next to a cold west-facing window in a heated room.