Those white dots resemble perlite. Pick one up, is it a piece of grit or a mushroom?

Perlite is lighter than water and may migrate upward when being watered.

Agree it sure looks like perlite but if it is tiny toadstools it is basically a normal response to overly wet soil. Your's looks quite wet in the pic and often, even when we think we aren't we usually are still over-watering ;-).

They pose no threat to any plants and will die off as soon as the soil dries out some.

If they really bother you just lightly rake them back into the soil surface.

Dave

Thank you all for the helpful feedback! My first thought was perlite and I know it's hard to tell in the photo but they are definitely small mushrooms.

I am sure I could be over watering. I will try to be more careful with watering and see if drier soil changes anything.

I appreciate the reassurance that they are normal - I was surprised to see such a big change in the course of one day.

Well, again, the point of watering is to keep the soil moist so seeds will germinate. So trying to keep the soil dry enough that mushrooms don't grow isn't going to help your seeds germinate. The mushrooms don't harm your plants. They'll go through their life cycle, die, and compost themselves. It is remarkable how mushrooms suddenly decide to sprout. They've got a mind of their own, I guess.

Now, I wouldn't eat them. Of course, I wouldn't take a mouthful of garden soil either. In fact, the mushrooms are just helping break down the plant material out of which they sprouted. I often get crops of mushrooms after I've mulched my soil with wood chips, and those mushrooms are helping compost those chips. So I would look at mushrooms as friends rather than enemies.

I have them in my flower garden are they dangerous my friend

I was right four years ago. Read it.