"Other people seem to start wth quite clean soil each spring!"...aren't you lucky you've proved that your soil is rich enough to actually grow natural things? By your definition, "clean soil" would seem to be "dead soil" as it wouldn't have anything growing in it, right?

If it is not harming anything you intended to grow in your beds, I would leave it be as it would seem to be part of the natural flora of your garden area. If it is harming your growth, put some of it in a sealable plastic bag and send it to your local Government Agriculture organization for identification. Send some soil in a seperate bag as they may need that to identify spores that lead to its growth.

Soil is an amazing substance, full of all kinds of things.

How close and what size are the nearest trees/shrubs?

tj

^^^ That would be my first question as well. Tree and large shrub roots can extend a considerable distance from the base of the plant and they will eagerly invade the enriched soil of any raised bed nearby.

This question comes up countless times and the answer is almost always the same.....tree roots.

(btw, roots do not grow from spores :-))

gardengal48...you may notice I don't use the word "root" in my answer at all...

Not to get too bogged down in the semantics of what is in soil, but grass is grown from rhizomes, as are many trees and bushes. Until the parent plant is identified, its extremely difficult to say whether that is root or rhizome. The simple fact that nothing has grown out of that tangled mass suggests strongly it is rhizome, still awaiting a favorable combination of factors to grow another of its progeny.

Feeder roots of maples(for one) have choked the life out of plants in many enriched garden beds.

tj

sturgeonguy, your experience with botany/horticulture seems to be different from mine :-) Some grasses are rhizomatous...but not all. And very few trees or shrubs are, given the multiple thousands of species that exist. And there is just as great a probability - in fact, probably a much a greater likelihood - that these are just the feeder roots of some not too distant, large growing woody plant that are seeking out a juicy source of moisture and nutrients in the raised bed. And will probably never generate any sort of recognizable topgrowth from that source.