I was just re doing it as it was already in place but needed weeding and more bark

I guess its been about 5 years since my wife and I put it in.
A lot of the old bark (I presume it was that as apart from the fallout from the apple tree in the same spot there isn't anything above the weedcloth under the bark) seems to have turned to soil - or at least something that will sustain weeds

How frequently should new bark be added?