Sunday, April 2, 2017

Dealing with Freeze Damage

I'm sure that all of us are dealing with damage from the freeze we had mid-March. After a very warm February, most plants had already begun to show signs of spring: deciduous magnolias and azaleas were blooming; and ferns, hosta, and other herbaceous perennials had sprouted. Then, on March 15, the nighttime temperature in my neighborhood was 26. Although I have a few frost blankets, I did not cover any of my plants. So many were at risk that the task seemed impossible.

Although it was sad to see so many plants suffer from the cold, it was interesting to see how the same species were affected differently, depending on the specific cultivar and location of the plant. Take azaleas, for instance.  Some of my azaleas had been blooming since early March, and the fully-opened blooms on these were completely ruined by the cold. This was not a terrible loss since their blooms would have been declining very soon anyway. On others (see picture below), the blooms froze on the parts of the plants that were more exposed (and thus the blooms were farther along),  and the parts of the plant where the buds had not yet opened were spared and have since flowered.

What to do about cold damage on azaleas? I don't intend to do anything until the azaleas have finished blooming. Then I'll prune as I usually do. Admittedly, the freeze-damaged blooms are unattractive and seem to be taking longer to fall off the plant than an undamaged bloom would, but I'll wait and see what happens.

Quite a few of our hosta were also damaged by the cold. Some had not yet broken through the ground, and others were barely peeking through. These were not damaged at all. Others had broken dormancy to various extents, and these were damaged to varying degrees. 

Here is a cultivar called 'Fragrant Bouquet' that had a few stalks emerged and was somewhat affected by the cold weather. The older leaves on the left side of the picture are a bit crinkled and deformed, but I will probably leave them on the plant and hope that the new foliage will be enough to disguise them.

Here is another 'Fragrant Bouquet,' planted in the same bed, that was completely turned to mush by the cold. Go figure. I will completely remove these stalks once the new ones begin to appear.

And finally, here is a different cultivar (not sure which) that was fully emerged when the cold came, yet seems to be unaffected.

For me, the list of plants affected by the late cold is a fairly long one. My hardy orchids (Bletilla striata) were fully up with buds about to open, and they were all killed back. They are cold hardy to zone 5 so I'm not too worried about their ultimate survival, but I don't expect to get flowers this year. 

The plants I worry about are the ones that are borderline hardy in our area, like the paperbush (Edgeworthia chrysantha). It had already pushed out new leaves, and they seemed to have been stopped in their tracks by the cold. They did not turn brown and crispy but neither have they continue to grow. 

The paperbush pushes up new shoots from the root each spring, seen as the green center in this otherwise still-brown plant. I typically cut these shoots back each year because I like the branching structure that is visible in the winter. This spring, I will wait to see how well the old part of the plant recovers. If it doesn't, these new shoots will become the plant, and I will cut away the old part. I don't think that will happen but I will be patient before pruning away the new shoots.

Speaking of patience, in one of my earlier posts, I talked about using a warm February day to cut away the old foliage on our autumn ferns. I wish I had shown more patience in that case. By cutting back the old foliage and revealing the crown to the warm sun, I encouraged early new growth that was too tender to withstand the cold temperatures. By cutting back too early, I left the tender emerging fronds to face the cold without the protection that the old foliage would have provided.

Hopefully, we are safe from freezes and frosts for this spring, but only Mother Nature knows. While the rule of thumb for the frost free date is April 15 for our area, it is good to be reminded that there is always the risk of the occasional exception. According to the National Weather service, the latest recorded spring frost date (36 degrees and below) for Memphis is May 4 and the latest freeze date (32 degrees and below) is April 25. 

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