Monday, May 05, 2008

Frost, Death and Growth

Plant growth is most notable at this time of year, when above-ground growth is just taking off. It was clear in my garden, as from the weather report, that today was the first significant growing day in about a week. For most plants, growth follows temperature in an almost linear response, from zero growth at 40F to maximum growth at 80F (leveling off suddenly, with distress beginning at 86F.)

What had shut things down, of course, was that after weeks with much warmth and without frost, we got a 25F frost in Adams last week, followed by cold and clouds. The frost had been predicted at least 5 days ahead of time on, and so I was ready, and put inverted buckets over the two Weigela "bushes" (a few inches high) I made from cuttings last June. The plants had overwintered successfully, and are generally considered hardy to zone 4, but I wanted to be sure of their safety. Fresh spring growth is far more sensitive to frost than is a dormant plant (if that weren't true, the plants wouldn't bother going dormant now, would they?), and tiny cuttings are less likely to have reserves of energy and bud tissue if they lose their growing ones.

As it happens, none of my other bushes or perennials suffered any significant setback -- a trivial one is mentioned below -- so I probably hadn't needed to protect the Weigelas. (Not that there was a downside to doing so.)

But I had forgotten to protect the one plant obviously sensitive to cold - a just-planted blooming pot marigold (Calendula), which was entirely turned to mush. Not valuing annuals much, or at any rate, not being afraid of losing them, I did not give any thought to that plant even though it was the only thing I had really blooming except for some of my daffodils, and even though it's native to the Mediterranean and Middle East.

So what was damaged? The bleeding heart (Dicentra spectabilis), the one plant which was just starting to open its blooms (the earliest blooming perennial of significant size, to my knowledge, and a great plant in part for this timing), seemed to have had its flowers shriveled a bit even though the plant itself is hardy to zone 3. The flowers and top-growth are still a bit small and limp, but not dead.

Finally, most of the pink magnolia trees in the area saw their magnificent flowers turn to brown mush overnight. Perhaps they had another week in them. Magnolia x soulangeana is hardy to zone 5, but those ratings refer to the plant's reliably not dying, not to its never losing flower buds.

Speaking of hardiness, I once had a conversation with a local woman who told me that she had planted some Gladioli and then never lifted their bulbs, and yet they came back strong for a couple years, until a (probably colder) winter killed them off. I left some Glads in the ground last fall, since the late-planted ones would probably not have the energy to bloom again this year anyway, I felt like trying something else in their place, I am always looking to experiment, and I am lazy.

As it happens, those Gladioli in the normal ground position and in turf all died (nothing came up), while one I had planted in the best-drained position possible (in loose earth just inside the loose rock wall of a 2-foot-high raised bed) has come back this spring, although apparently having split into separate little bulbs (there are several growing points). This makes sense. I had read (e.g., by the late Christopher Lloyd, IMHO the greatest of garden writers) that for many such Mediterranean plants, hardiness is more a matter of drainage than of absolute temperatures. (This winter's snow cover may also have helped.)

Does anyone know of anything else damaged by last week's frost, or have a surprising tale of hardiness?

1 comment:

DWPittelli said...

As it happens, even some late-planted Gladioli in turf and in a not-very-well drained cultivated bed have come up, and are almost a foot tall as of June 18.