Crumble is the decayed heartwood of trees, or rotten wood. You have to go
to some trouble to collect crumble. There are many different kinds. It was
the first mulch. It has an interesting historic background, if anyone is
interested. I have played around with different uses

I have been growing marginals in it (sometimes I add sand) - in pots. Most
plants do not do very well with just crumble, although I gather it would
be good for orchids. I sometimes leave two or three inches of water on top
with the marginals. Most marginal and water plants do fine, but are not at
all rampant growers. Although it has been very hot and muggy, there have
been no mosquitoesin the water, although this is something that I normally
watch for. I don't use dunks or anything like that. I have also used
crumbled up leaves and soil in some of my marginal containers. The water
can look like tea. No mosquitoes there either. Is there something about
these byproducts of wood, that prevents mosquitoes? Or have I just not
been bothered by mosquitoes this year.