“What is wrong with my plants this year?”
— Amy Heifitz, Hoffman Estates
The plants in your photo appear to be getting too much sun, which is scorching the leaves. The damage on the hosta leaves is easy to see with the bleaching and visible burning of the leaves. Hostas planted in sites with too much sun can show more subtle symptoms with an overall bleaching of the color (like a less vivid blue) and less contrast in the leaves’ variegation. Some hosta cultivars have more resistance to sun. The damage on your Japanese forest grass is less pronounced, with browning visible only on some of the leaves. This helps confirm that too much sun is the cause.
It is likely that something changed in the area surrounding the plants that increased the amount of sunlight enough to start damaging the plants compared to past years. Removal of a large shade tree can dramatically increase the amount of sunlight reaching a bed and have immediate impact on the plants. An adjacent shade tree that has been in slow decline over several years with decreasing foliage can also slowly increase the amount of sun to a planting bed. Plants respond more dramatically once the extra sun becomes too much. There have been some very sunny and hot days this year, which may have increased the damage.
Increasing shade from growing shade trees over a period of years can also affect adjacent plants that are sun-loving. The impact is generally gradual as the amount of shade increases year after year, so gardeners do not always notice until the plants’ performance has been significantly affected. Sun-loving plants in too much shade have less vigorous growth and diminished flowering. Some pruning of shade trees can increase the amount of light, but it is best not to over-prune a large shade tree.
Installing new plants that prefer more appropriate light levels is a good strategy. Increasing the sunlight enough under large shade trees for sun-loving plants is not feasible in most garden situations. Replanting shade trees to increase the amount of shade for shade-loving plants works, but takes time for the trees to get to a big enough size. You may need to switch plants to ones that are more sun-tolerant.
Provide supplemental water during dry periods to help reduce stress on the plants.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.