Sounds like algae. So, yes, it needs to dry out!

Without a photo, it's difficult to say exactly what might be going on......some granular fertilizers will discolor and look moldy once they become wet; ditto with some common insecticides. Also fresh mulch can begin to decompose very rapidly in warm weather and plenty of moisture and that can produce various fungal organisms that look like mold.

It could also be algae growing in excessively moist soils. Automatic sprinkler systems are seldom set to benefit the plants properly - coming on daily for 5-10 minutes really does very little good and is likely a waste of water. It would be much better to water once or twice a week but for a significantly longer period - as much as 30 minutes depending on soil type.

Mold in the garden is not the same as mold growing indoors - most outdoor 'mold' is just the mycelium or fruiting bodies of various soil fungi going about their usual business and are almost always harmless. Algae, while not necessarily harmful on its own, can indicate a very wet or poorly drainage soil situation and that can be harmful to many plants.

But only a photo can confirm exactly what's up :-))

If it is growing on top and is blue-green and a bit slimy, it is probably nothing more than a simple green algae. It's harmless, but it's a sign that the soil is probably staying too moist.

It would help if you can post a pic.

Keep track of how long and how often the sprinklers are running....or inspect the controller settings yourself. If the box is locked, put a note on it for the landscaper. Landscapes can be ruined by improperly set irrigation.

Blue green algae is a fairly common problem on soils that are kept too wet. The solution to that is to allow the soil to dry out and then stir the soil a bit. If you have any type of respiratory problem, Asthma, allergies, use care when messing about with this although an N95 dust mask should be enough protection.

This post was edited by kimmsr on Mon, Sep 23, 13 at 7:05

Mold on the surface can be due to the following:

--- Too much rain/water before to get a chance to dry up.
--- Too much shade, cloudy days, not enough heat an sunshine.
--- Fertilized with too much Nitrogen
---- The soil is acidic.
---- the bed doe not have good drainage and stays wet too long.

I have noticed when I cover the seeds or lightly mulch them wit peat moss, molds grow on it more.

So, it is better to mulch with some very coarse compost, so it can aerate and dry better.

Sure won't be good for the roses to be that wet!