I live in Massachusetts and have a swath of pachysandra approximately twelve inches wide growing against the foundation around my house. It's healthy and produced a lot of pretty, sweet-smelling flowers throughout the summer.

We recently trimmed a section and, as you can see, there's a green substance on the concrete that looks like algae. Is the pachysandra causing that? Is the algae dangerous to the concrete? If so, is trimming the plant enough or do we actually have to dig it up? One of the reasons we like it is because it hides the ugly foundation, so I'll leave it unless advised otherwise.

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The algae is there because of the dim lighting and moisture. It will not harm the concrete. In some cases, it provides an area for moss to spawn, which can hold in moisture, but in most cases, it's harmless (except aesthetically).

At my place, it's shady enough that over half the foundation gets a layer of this algae on it yearly, so it's a regular chore to clean it off the areas where there isn't ivy on the wall, just for looks.

It's not the pachysandra, although that may help shade the wall some. You can wash the algae off with a pressure washer or a scrubbing brush. Or you can grow something over it.

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