I seem to've acquired some gravel that was loaded with moss spores. All is in full sun and in large raised beds so water & shade are not the problem. Some threaten to grow over the semps. Can I use ferrous sulphate ott (over the top) of the semps to control the moss? If not, what CAN I do to get rid of the moss. Hand-picking is out of the question (too much square footage). Thanks for any help.

Hi Kate. Let us see what Dr. Houseleeks has to say about this problem. It is some what of a problem for me this year because of moderate winter and spring we have had with almost non stop rain. For me I know it will go away when the dry warmer weather arrives.

Hi, Kate,

Loved the plants we traded a while back under a different handle elsewhere.

I, too, have lots of moss in my semps. So far, it has not been a problem for me, other than some anxiety over thinking the plants are too wet. I've never had to treat moss but understand that iron sulfate (ferrous sulfate) is the most recommended way of doing what you want. I could not find any references to the treatment being harmful nor safe for sempervivum and relatives.

Moss is not known as being highly competitive with other plants. The general advice is that if you are experiencing a lot of moss, then the area where the moss is growing is out of balance for some reason. Too much moisture, too much "trash" in the ground (read:nutrients) getting too much light, not enough actively growing plants are the main causes. If plants are planted closer together, then you will find that you do not have a moss issue with them. I know that in those cases where my semps are over-potted (pot too big for the plants) I will see moss. So, if your plants are in beds, try planting them closer together. With semps, that may mean your rosettes do not get as large as they might otherwise, but the moss should abate. If in pots, try keeping them in smaller pots until they really need a larger size.

You indicated you wanted to try a chemical solution, but we do not know if it will be safe for the plants. In cases like this, probably you will need to run your own experiment. Choose some plants for which you have duplicates or plenty, choose an area that is isolated so that run off will not get other plants, then treat with recommended dosage of your moss-deterrent of choice and watch for the results.

When you get your results, please share them with us as I suspect your problem is more common than one might think.

I've had good results using dolomite lime as an organic remedy for moss. Moss seems to like acidic conditions, so if you can alter the pH it won't like that. There's no guarantee you'll get rid of it all, but it might make is less obvious.