What Is Wrong With My Gravel And How Do I Clean It?

Question

We laid 20mm shingle on membrane in our garden around 3 months ago. All is great except for a small 2m square section that has gone really black and dirty. This section is under shade from a tree and I’m guessing that’s relevant. I have tried rinsing and stirring a bucket at a time in hot soapy water but no real improvement. Does anybody know what the problem is and how to treat it? Thank you.

Answer 1

This is common under Hackberry trees, as well as many other species. Sap will leak from the tree and onto anything under it. This sap will contract sooty mold and begin to turn black.

Here is an article that will help you to remove it:

https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-remove-tree-sap.htm