The mushroom compost would be fine. You can also cover the root area - as widely as possible, even beyond the drip line is best - with any organic (in the sense of natural, i.e.; shredded bark, wood, leaves, compost, etc., not in the meaning of chemical free, and not gravel, although in the right place, that's also attractive, and fulfills the other requirements) mulch, putting it no deeper than 4", and putting no mulch in the 2-4" next to the trunks of the plants. Mulch will eventually break down - one reason to use it, others being limiting weeds, keeping root areas cooler, and keeping moisture in the soil - so you will need to add an inch or so per year, if you do begin. Mulch also breaks the force of water, so is more likely to stay put, and not wash away like your soil did. If you are planting on a slope, avoid pine bark - it tends to float and wash away.

You can use a "natural" fertilizer, such as cottonseed meal or alfalfa meal, compost or one of the Organic fertilizers (of whatever brand you chose; Espoma is a good one, 'though not all the types are purely Organic) lightly before spreading the mulch, as they are mild and not likely to burn. If you plant to use a chemical fertilizer, then I would spread an inch or two of whatever you use as a mulch down first, as the chemicals are much more water soluble, and might burn the exposed feeder roots.

I trust this has answered your question, and not confused you further!

Thanks dibbit!
That is what I needed to know.