sunburn on hosta leaves
Have you noticed your hostas looking a little pale and papery in spots this summer? It’s the effect of the intense hot summer we’ve had, which is having a severe impact on our lush, leafy perennials, especially hostas. Hostas, grown primarily for their foliage, are basically all leaves, and their huge amount of leaf surface makes them very vulnerable to sun damage. A hosta’s neat rosette of attractive leaves, facing upward towards the sun, just like a person lying on the beach, is almost asking for a sunburn.
But it’s not only the heat. Another unfortunate feature of our drought is endless days of cloudless skies, great for golfers, but not for leafy plants. The sun has been unrelenting. The lack of any cloud cover has been a huge factor in causing the sunburn damage.
Sun damage to hosta leaf.
Hosta’s large leaf surface lets a lot of moisture out easily as well, through transpiration, which is only worse on a hot sunny day. A leaf that is full of moisture can defend against the hot sun, a leaf that is stressed from drought has no defense. This is why hostas that are planted in the sun need more watering, in general.
Hostas are considered shade loving, or shade tolerant. They need just right conditions, neither too deeply shady, nor too sunny: like all plants, hostas need some sun. Most, however, do not like full sun, especially the blue hostas. These have a kind of waxy coating on the hosta leaf’s outermost ‘skin’, or epidermis.
The glaucous appearance of blue hostas is caused by light-scattering crystals in the waxy coating.
This coating also makes raindrops bead up on hosta leaves. The waxy coating also prevents water loss, and also gives it that dull sheen. However, in intense sun the waxy substance breaks down, and ‘melts’, leaving the leaves even more vulnerable. Blue hostas should always be planted where they get shade for the hottest part of the day. A blue hosta in full sun, will be less blue. Morning sun, or daytime dappled sunlight is ideal, and full sun for hours on end is really not a good idea. Think of time of day too, as full sun at 9 am is different than full sun at noon. I have some hostas that used to grow under the shade of a large tree, which sadly, fell down. Now they are growing in full sun and are not too happy. I have to consider moving them to shadier pastures.
Which are the most sun tolerant hosta varieties?
Most sun tolerant are hostas with fragrant flowers, bred from the species Hosta plantaginea, which originated in warmer climates. I am a big fan of fragrant hostas, as their scent is exquisite. The flowers, which can be brought in as cut flowers in a bouquet, are also magnets for pollinators like bees and even hummingbirds. ‘Sun Power’, ‘August Moon’, ‘Sum and Substance’, ‘Honeybells’, ‘Sundance’, ‘Fried Bananas’, and ‘Sun Glow’ are all sun tolerant varieties, and more are listed at the link above.
Hostas that can take more sun, like many yellow ones, for example, do need more water to cope with the higher rate of transpiration in sunnier spots. The combination of drought, and intense sun makes a dangerous pairing.
What can you do to protect your hostas?
- Plant in the right place.
- Water more if planted in full sun.
- Consider temporarily covering prized hostas with a light-weight cloth during the hottest part of the day during heat and drought periods. Or use a well-positioned umbrella to protect against the hottest sun.
- Dig up and relocate a hosta to a shadier place if it constantly burns in sun. You can divide it at the same time, giving you another benefit. Early spring and fall are the best times for division.