It is common to find plants with rock mulch on top of the soil or pot. This may be glued on, which poses a problem for transplanting. Glued rocks in potted plants prevent problems when shipping as plants tend to fall over and can lose their soil during shipment. When this happens, the plant will likely be dead on arrival as exposed roots mean a slow, lingering demise. Preventing soil loss is not the only reason this practice occurs, but is the most functional one.
The rocks glued to the top of the pot are acting partially as a mulch. Mulch can help keep pathways in beds clear of debris and mud. Mulch can keep plant roots warm in winter and cool in summer. A layer of any type of mulch will prevent excess evaporation and moisture loss. There are organic and inorganic mulches but the rocks on the top of the soil are an inorganic type. In addition to rocks, inorganic mulches include tires, sand, crushed brick, recycled glass and many more materials.
In potted plants, the glued down rock is also used to prevent moisture loss. Potted plants have less of an area to draw moisture from than a plant in the ground. The pot has all surfaces exposed to air, which increases evaporation. A layer of gravel or rock on top can help prevent excess drying. Care should be taken on plants grown in hot locations. Rock will absorb and transfer the intense heat and can make soils dangerously hot. It is best to remove the glued down rocks for plants that will grow in full sun.
Decorative and Preventive
A layer of glued on rock on the top of a plant adds an ornamental touch. There are colored rocks and a variety of sizes, textures and types. They are commonly used on plants which grow in rocky areas to simulate the terrain in which you would find the specimen. Cactus and succulent plants are often found in nurseries with a glued rock coating on the surface of the pot. Glued rock mulches also prevent some pests and weeds from establishing in the plant. Tiny, thickly glued rocks leave no room for weed seeds and larger insects to encroach on the plant and soil.
While a mulch may be beneficial, a glued-down mulch that consists of a layer of rocks can make re-potting and some general care difficult. In order to remove the glued-down rocks, soak the entire plant in a bucket of water. You will have to weight it down enough to submerge the mulch. Soak overnight and the mulch should peel off. Re-pot your plant and add an organic or inorganic mulch of your own, which can be removed for general maintenance.