Azaleas and rhododendrons have shallow roots, and can suffer badly in dry weather: a good moisture-retentive mulch is therefore vital. Peat is an obvious choice for such acid-loving plants, but only so long as it’s wet. When it dries out, it forms a crust that can actually throw off water.
Shredded or pulverised bark is better, but expensive unless bought in bulk. Don’t be tempted, by the way to buy bargain lots of cheap unbranded bark. It may not have been properly composted and could still contain toxic residues.
One of the cheapest mulches is pine needles, which you can collect for nothing in woodland – provided, of course, that you have the owner’s permission. Spruce or other conifer needles will do the same job, but they’re more prickly and more difficult to handle.
Using stone mulch also looks good with azaleas and rhododendrons.