The term, mulch, whose original meaning was "rotten hay," is most likely an extended use of a Middle English word meaning "soft, variant" which, in turn, is derived from the Old English, mylsc which meant "mild, mellow". Applying mulch to roses is an attempt to make the life of the rose softer, milder and mellower through the medium of " rotten hay" or a similar protective cover. Mulch is a material placed on the soil to shield it from the elements taken in the broadest sense of the meaning. Inorganic mulches are those derived from inanimate objects which will shield the soil but add nothing to it. Organic mulches were originally some type of plant material which eventually decomposed and enriched the soil by becoming part of its structure. Inorganic mulches are less expensive since they do not decompose and do not need to be supplemented very often. Organic mulches may cost less for the original application but, once they decompose, will need to be replaced or supplemented.
Inorganic mulches include gravel, stone, crushed brick, white marble, volcanic rock, water-worn pebbles and landscape fabric to name a few. They do not blow about in the wind, harbor insects or diseases or rob the soil of nitrogen. They can be used in a variety of settings. Their disadvantages include working free of beds to areas where they might become a nuisance or even a danger if hurled by a lawn mower. Unless underlaid with landscape fabric, the stones may be pressed into the soil. Dark stones will absorb heat into the soil while light stones such as marble may reflect enough heat to damage tender plants. Limestone, as well as marble chips can raise the soil pH to the detriment of acid-loving plants such as azaleas and roses.
The list of organic mulches is almost endless but rose growers may reject many of these as not elegant enough to enhance their roses. The following mulches can be used in the more prominent locations usually inhabited by roses. Grass clippings which have not been treated with herbicides give good weed control and are an excellent source of nitrogen. They should be dry or if not, should be gradually built up and not placed directly against the rose. They are rather unattractive but they may be hidden with a more attractive layer of pine needles or bark.
Bark and wood chips give good weed control, are slow to decompose and will stay in place. Both make attractive covers especially if the bark chunks are not so bulky that they dwarf the rose canes. Cypress mulch will last longer than the hardwood chips and thus may be less expensive than some of the other mulches. A layer of leaves, preferably oak leaves, makes an attractive as well as nutritious mulch for roses. Leaves provide good weed control and, although they decompose quickly, are a wonderful amendment to the soil. Cocoa shell mulch, among the most expensive of mulch products, is very popular for roses even though its strong chocolate aroma does not last. Any of these mulches may be underlaid with landscape fabric for extra protection.
The mulch depth will vary depending on the product used. Inorganic mulch layers are generally less then one inch. Organic mulch layers range from two to four inches deep.