Q: My Lily of the Valley plants have large, brown spots on them. Many of them are turning brown like someone sprayed an herbicide. What is wrong with them?

• Marilyn from Canfield

A: Many of us love the spring blooms of Lily of the Valley (Convallaria majalis). The scent is amazing and the plants spread fast, making for a great show each spring. But this plant spreads quickly through its rhizomes. For this reason, this plant commonly overcrowds the garden. I wouldn’t say it is invasive, but it will fill in an area.

When the plant becomes crowded, it is increasingly susceptible to disease. This is especially true in areas where the plant’s leaves stay wet (no morning sun) for several hours a day. Besides overcrowding, other factors such as limited airflow through the planting create the perfect environment for disease to flourish on this plant. Fall clean-up of the leaf and stem debris is paramount to reducing infection in next year’s growth.

This year the disease is evident, but not terrible due to our dry weather. But, in wet years the disease can get so bad that the entire leaf from the stem can turn brown.

If you look closely, you will still see several rings of darker brown areas where the disease first began development. While it might look cosmetic this year, the disease development can make a leaf turn brown in just a few days under perfect conditions.

This plant already has stored root reserves for next season, thus removing the leaves will not have a detrimental effect on next year’s blooms. So, you can cut the plants down to reduce the impact of infection this year.

When you do this, you may want to thin the plant population by at least half to increase airflow in the area next spring.

A generally accepted practice would be to thin the area by 1/3 in June each year to promote good plant health if the disease persists every year. This plant is aggressive, but not invasive, so it will fill back in before you know it!

For details on control options, visit: http://go.osu.edu/lily.

For more details on this plant, go to https://go.osu.edu/lilyvalley.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. For more details visit http://go.osu.edu/mahoningclinic.