Hi -- I've built 2' high raised beds out of stone (many of them, 6 tons' worth!) over the last year, and planted a variety of shrubs and perennials. Not surprisingly, the soil is settling. (It was also covered with a fine shredded cedar mulch.) Here's my wondering: In the natural world, there aren't humans to lift plants up as their crowns are gradually covered with leaf mold, blown soil, conifer needles, sand from disintegrating sandstone, etc. Yet we're always told not to just add soil to the top of a bed if the level sinks, but to raise the plants so they're always at the same level. This does not make sense to me. I would think that if the compost, soil, manure, mulch etc. that one adds to a raised bed is not added in huge amounts all at once, but in several stages over a year, it shouldn't be any more harmful than in the wild . . . and the plants' roots will work them up to an optimal level without my intervention to raise them . . . or am I wrong? Thanks for your reply!
The important thing, I think, is to bear in mind the weight and texture of the natural forest debris (fallen leaves and needles, mostly) that collects around plants in the wild. It's light-textured, fast-draining, and tends to quickly decay and become integrated into the soil by earthworms, insects and what have you. Soil or a heavy layer of manure or even a very heavy layer of compost is different -- heavier, less free-draining, and in the case of soil will never completely decay but will lie on top of the existing soil and roots. That's where the need for caution comes in. Some plants are especially sensitive to having extra soil placed over their roots, and such plants are frequently killed this way. Others are more tolerant. I've never seen a comprehensive list of which is which -- just isolated tales of woe from gardeners who lost, say, a planting of rhododendrons. (For myself, I banked new soil too deeply around a newly-transplanted clethra a couple of years ago, and by the time I discovered the error, the plant had simply produced new roots from the buried part of the stem. But I don't think I'd try this with, say, a dwarf conifer.) By the way, congratulations on the Herculean accomplishment of building raised beds out of stone! My big garden project this year was an herb-garden labyrinth with pathways of native stone, and I only managed it with the help of two sons and a nephew doing the grunt work.
