Hail Can Be Hell on Plants

     Yes, it's been unseasonably cool and wet here in Northern California this spring, vexing area gardeners. The temperature has yet to hit 90, a Central Valley tradition that typically begins in early May (or sooner). Another anomaly of our cool, wet, late spring weather in Northern California: the frequency of hailstorms. These short bursts of ice pellets falling from the sky is more of a March weather event here. That time of year, though, gardeners see less damage to their plants, simply because of less development of new stems, leaves and fruit.

But such a storm in late May? Such as the half-inch hail that pounded parts of Sacramento County on May 27?

Then, all hail breaks loose in the garden.

The most obvious sign of hail damage is tattered, torn, tender leaves. That, a gardener can usually live with. New leaves will probably grow in their place. However, another sign of hail injury to leaves is the grazing or pitting of the leaves. Don't confuse that with foliage diseases. One good way to figure out if it was hail or disease: hail injury will occur usually only on the upper portion of the leaf. 

Hail injury on other parts of the plant, though, may be trouble ahead, especially with soft fruit.

Hoticultural Snob Alert!

Cane berries, cherries and grapes, especially those in the post-veraison stage, can end up bruised and cracked by a hailstorm. "Veraison", by the way, is one of those 50-cent, snooty horticultural terms grape growers like to toss out in casual conversation, to make them look like snobby French wine experts. "Change of color of grape berries" is the literal translation. Veraison refers to the onset of ripening, when the berry is full grown and the color is changing.

After a May hailstorm, chances are you won't see damage on ripening grapes later in the summer, since most are small and hard at this point. 

But check out your brambleberries, blueberries and raspberries. Many of those are fully developed at this point (post-veraison. Use it in a sentence today!). Look for hail damage on the upper portion or the windward side of these fruits. Openings in the fruit can serve as entry points for certain fungal diseases, such as botrytis and other fruit rots.

If you see injured berries, it helps to pray for dry weather. Once you get up off your knees, though, help the fruit along by increasing sunlight penetration and air circulation by removing leaves around damaged fruit, being sure to remove those leaves that are touching the fruit.

Hail Damaged Apple

Maturing fruit on your other plants may look fine now, but those little hailstone scars can enlarge as the fruit grows. Both stone fruits and citrus are subject to this scarring. Again, look for damage on the portion of the fruit that is facing the sky.

Hail Damage on Citrus

The excellent book, "Abiotic Disorders of Landscape Plants" from the University of California's Agriculture and Natural Resources Division, also point outs these other hail damage symptoms:

Twigs may be broken.

Bark may be bruised, broken or scarred. Hail wounds on bark are usually elliptical and vary in length from a fraction of an inch to four inches or more. 

Hail wounds occur on the upper side of the branches and on the side of the plant facing the storm. Those bark injuries may serve as entrances for decay-causing fungi.  

According to the University of California-Davis, anthracnose lesions on small grape branches may be confused with hail injury; however, unlike hail damage, the edges of the wounds caused by the anthracnose fungus are raised and black. In addition, hail damage generally appears on only one side of the shoot, whereas anthracnose is more generally distributed.

And, hail that gathers on tender, low growing plants may cause low temperature injury. Chances of that happening in May, though, are rare in California.

 

So, what's a gardener to do? 

Keep treating your plants right. 

Improve the vigor of hail-injured plants with proper irrigation and fertilization, if necessary.