I was actually told that, eventually, compost should mostly disappear. It's organic. Except for a few inorganic components, it eventually goes away.

So I guess the full answer to that is no. Not unless you eventually want no soil left. But that probably takes a really long time.

But apart from the above, my rhododendron is planted in a really heavy soil (they're native to here) and does great. Our local pH is low, too.

@Simon You should add your climate zone to your name, per our normal conventions here. It helps a lot when reading many comments to know a person's climate context.

No, because it doesn't take long at all for compost to go away. Same reason you don't want to put it in a planting hole. I do use a deeper compost mulch than is generally recommended, but I keep it away from plant crowns. Annual plants can handle incorporated compost---as in your vegetable garden, say.

I’ve mentioned this before on the rose forum:

Three of my healthiest, most vigorous, most productive roses are Kosmos, Poseidon and Sunny Sky. One of each. Planted (bare root) in holes 24 inches wide and 16 - 17 inches deep - as far down as I could go in hard clay and rocks. Native soil moved elsewhere; holes backfilled with 100% compost, partially finished. Zero percent mineral soil.

That was 6 years ago.

Every year there’s a little subsidence. The last 2 years I topped up with a 50-50 mixture of vegetable bed (high OM) clay, and compost from the pile. Prior to that yearly compost alone. And a cup of Hollytone each spring.

I didn’t set out to experiment. Rather, I didn’t know better (in 2016).

So much for what one should or shouldn’t do.

I’ll stop at that; I’m getting close to quoting from Oscar Wilde.

Continuing with the anecdotes when I worked at a commercial rhododendron production operation, we potted the rooted evergreen azalea cuttings in pure fine grade bark mulch. However, the owner-operator did water these with a fertilizer injector afterward - so it was kind of like he was growing epiphytic orchids.

When I dug up an established rhododendron planting at my previous habitation in order to do something else with the space, I discovered that the entire extent of rooting out by them had been in the bark mulch. That there was no root growth extending out of the original field soil root-balls below the mulch level, and into the existing soil.

In the very rainy summer climate regions where the majority of wild rhododendron species occur dead logs, live trees and rock formations are often typical growing sites in forested settings. Where the shrubs live in the organic accumulation present on these features, completely separated from Mother Earth.

This includes limestone areas, where the calcium content of the rocks is not a problem because the rhododendrons are growing only in the organic material on top. And rainwater penetration moves through the rooting zone toward the stone base.

@Embothrium Adding to your comment, I have noticed that maybe 20% of the Rhodie growers I have had conversations with grow container plants in pure bark. Now bark is not exactly compost, but this is a container environment where you need to worry about a perched water table. That did get me to wondering whether - in a raised bed environment - garden waste compost would at least not kill the plants. It might be worth an experiment with a single plant.