Our backyard (which is flat and no pine trees) has hundreds of tiny mushrooms throughout the grass. Our front yard (which has a slight slope and one large pine tree) has many huge mushrooms. Otherwise, we have good looking grass. We have lived here for a very long time without ever seeing this problem. I know one answer is to “sweeten” the soil with lime. Should we do this now, in the fall, or at what time of year? Should we remove the mushrooms or let them be? Any other suggestions?
University of California, Davis Integrated Pest Management has guidelines on managing mushrooms in lawns. Here is an excerpt:
“Mushrooms found in lawns often develop from buried scraps of construction lumber, dead tree roots, or other organic matter. The fungi that produce these mushrooms are beneficial because they decompose organic matter in the soil, making nutrients available to other plants. These mushrooms usually are harmless to grasses, but some people consider them unsightly or want to get rid of them because young children play in the area. Remove mushrooms growing from buried wood or roots by picking them as they appear or by digging out the wood. Many of these mushrooms are associated with overirrigation or poor drainage. Removing excess thatch and aerating the soil to improve water penetration may help in some cases.”
The website further suggests adding nitrogen fertilizer, but bear in mind that excessive fertilizer contributes to urban runoff pollution.
As for sweetening the soil with lime(making it less acidic), it is best to do a soil test before attempting to amend for soil pH. The City of Seattle’s Natural Lawn Care information says that you would only need to “apply lime in the spring or fall if a soil test shows a calcium deficiency or acid soil conditions (pH less than 5).”