It appears that the mulch is staying moist on top. Watering deeply once a week or as needed encourages deeper roots. Shallow frequent watering encourages shallow roots. Sometimes with frequent rainfall mushrooms appear on wood mulch. Stirring the mulch up so that the top dries should get rid of them.

The mushrooms are a non issue. Wood mulch and organic matter combined with moist soil will sometimes result in the growth of mushrooms. There is nothing wrong with your soil and the mushrooms aren't hurting anything. My only advice is to get rid of the moisture meter and instead learn how to tell the soil moisture by the way the soil feels and the way the plants look.

Rodney

Hi - a Master Gardener here - in my training we learned that mushrooms are a sign you have healthy soil. Some folks even buy a type of mushroom spore to add to the soil. I wouldn't worry about it unless you don't like the look.

Are these mushrooms dangerous to dogs?