Plant Sunburn
July 17th, 2012
Somebody ought to invent sunscreen lotion for plants.
Heat alone can cause hydrangeas to do this.
These bouts of glaring sun and near-triple-digit heat are punishing to plants, particularly ones native to climates that don’t act like this. Plants that prefer a bit of shade but that you’ve got out in full sun aren’t faring any better.
As you might’ve noticed in the last few weeks, it’s not just dry conditions that can take a summertime toll on plants.
Flat-out heat and broiling sun can cause botanical suffering even when soil moisture is good.
This is usually the answer to the forlorn gardening question/apology, “But I don’t understand why my shrub (or tree) is turning brown. I’ve been keeping it watered.”
It also answers why your hydrangeas have been wilting even though you’ve been watering them. If they’re perked up in the morning, it’s not the dry soil causing them to wilt. It’s the heat.
In my own garden, I’ve got a couple of dwarf conifers that have been partly browning over the top. One is the dwarf Korean fir ‘Cis,’ and the other is a fine-needled dwarf sawara cypress ‘Cumulus.’
I’ve seen similar symptoms on bird’s nest spruce — a low form of Norway spruce.
My new "brown-variegated" Chamaecyparis pisifera 'Cumulus.'
The common denominator is that none of those like super-hot summers. They’re happy in the Pacific Northwest or New England or Norway — not Dallas, which is more like we’ve been having lately.
Water helps a little in these heat-related brown-outs. It not only sidesteps the double-trouble of dry soil and high heat, but water also cools the soil and by extension, the plant roots.
A couple of inches of mulch over the soil also helps, as does erecting a burlap, screen or shade-cloth protector to block the afternoon sun. I’ve employed a couple of patio chairs to give this kind of afternoon help to a recently transplanted crape myrtle in my yard that’s been wilting. But the real answer here is for the temperature to return to saner levels.
Our bake-oven conditions also have fried shade plants that are out in too much sun.
The most graphic example I’ve seen lately is also in my back yard. Up until this past winter, I had a patch of pachysandra groundcover growing nicely under a 25-year-old apple tree. But voles girdled the trunk over the winter and killed the poor tree. Without the shade-giving canopy, the pachysandra in this now-sunny area has literally melted into gasping brown the past two weeks. Just a few feet away — where the same planting is still under the canopy of an American fringetree — the pachysandra remains green, dense and unfazed.
Pachysandra in new sunlight has turned brown. Notice it's still green and unfazed where there's still shade.
Now that we got a 1.25-inch soaking on Sunday, I’m going to cut back the pachysandra and hope it regrows a more sun-tolerant set of leaves until my young replacement tree (a dove tree) replenishes the shade. Otherwise, the alternative is to yank the pachysandra and replace it with something more sun-preferring now that the conditions have changed.
Oh well. It’s all part of gardening.
Things change. And both we and the plants either roll with the punches or throw in the trowel.
But at least with the heat, WE get to go inside in the air-conditioning.