The graywater trench filling with mulch is a continual process. Others who have tried similar projects indicated it is possible to call lawn services who would be happy to drop off tree chippings so they don’t have to take them to the dump. We don’t need the trench filled overnight and have started by using the pine needles from the trees in front of the house and grass clippings from our tiny lawn. We have been able to use all the leaves from the Arizona ash when they fall in December. Unchipped sticks do not break down well, so although we trim shrubs, the clippings do not end up in the trench. We did have a compost pile in our kitchen garden. The dried, uncomposted material was moved to the new ditch. What is left to be seen are swarms of pill bugs – the predominant composter in our neck of the woods, er, cacti.
As of early August after construction, the ditch is filled about a foot from the top with local mulch. Also note the hole awaiting a fruit tree or two.