What Is the White Powder on my Terra-Cotta Pots?
Terra-cotta pots are porous, meaning liquids and tiny particles traveling through the material when it is moist. Water traveling throughout the grass carries it salts and minerals from the soil within, leaving white, chalky areas on the outside of the grass. These areas are particularly noticeable once the grass dries. White powder does not signify that the grass needs to be discarded — this discoloration could be removed.
Fertilizer Leftovers
Fertilizers from the soils include salts and minerals that absorb in the soil, particularly when moisture is present. Over the years, particularly with over-fertilization, a few of these salts and minerals may wind up within the grass itself, eventually making their way all the way through the outside.
Hard Water Deposits
Tap water includes minerals like calcium that could leave deposits on items where evaporation occurs, which is the reason why shower heads and spigots occasionally show a whitish residue. The same thing occurs in terra cotta — the grass absorbs the water and the minerals within it. When the water evaporates, the minerals don’t, leading to that white powder.
Preventing White Powder
Watering the plants using rainwater or distilled water helps prevent chalky residue from accumulating on the outside of terra-cotta pots. If the same plant was in the grass for more than six months, then leach the soil by running water to equal half the volume of soil through the grass — ideally, use rainwater or distilled water. Any white residue noticed atop the soil should be removed before leaching to prevent the vitamins from making their way into and through the terra cotta.
Brush it Away
Oftentimes, the white deposits may be removed by brushing the grass surface. Try a nylon-bristled brush to begin with to prevent scratching the grass, like a brush used for household chores. Follow up with a wire brush, using caution not to press too hard in case the pot is delicate enough to show scratches or damage.
Crud Cleaner
Clean off what is left of the residue after brushing by mixing equal parts water, rubbing alcohol and white vinegar, then rubbing it over the pots inside and out using a sponge. Vinegar dissolves the minerals while alcohol helps clean the pot.