What is this powdery stuff in my soil?

[SpringHasSprungTheGrassIsRiz]

Nothing on the surface, but when I got into my new bed, about a couple of inches down the ground is white, almost like ash. Any ideas?

Chalk?

Fungus possibly? Difficult to tell from the pics. If its fungus then that is a really good sign that the soil is really healthy.

Looks a bit like cement. Is this a new bed in a fairly newish building? Could just be the remnants of the builders mess under the top soil they put on top. My house is a 90's builld but in most beds I've dug there has been a layer of bits of cement, broken sewer pipes, rubble, tarmac from when the previous land use was demolished and then they out our houses on top.

Looks like mycorrhizal fungi. Very good for the soil and it has a mutually beneficial relationship with plants. They actually sell it as a soil additive in garden centres - one make is called Rootgrow.

Oh, I do hope it is helpful fungi! That would be great. The new beds were previouly lawn and unlikely to been anything other than grass ever. Not a new build (old farmhouse) so not new build rubble - although having been a working farm we do find all sorts buried around the place!

You could do a ph test on the soil. That would rule in/out chalk and cement.

It looks like mould/fungus to me.

Definitely looks like the mycorrhizal fungi. I am always pleased to see it, it means the soil is alive and working well.

I was going to say it looks like salt (or some soluble mineral) but I wouldn't know what those fungi look like so could also be that. Has stuff been growing well in that bed?

@DierdreDaphne it was under the lawn until last weekend, no visible issues with the grass.

It's harmless funghi. Probably caused by the organic matter under your lawn sitting in compacted and wet soil. Nothing to be concerned about at all and just a natural thing.