The Q&A Archives: Terra-Cotta pots: to seal or not to seal?

Question: Is it preferable to water-proof the inside of terra-cotta pots with a sealant? The terra-cotta pots will be placed outdoors (coastal San Diego,CA.). The pots will house Gerbera's, Calla Lilies, herbs, Gardenia's (Gardenia's are a challenge).
Thank you for your help.

Answer: Before deciding whether or not to seal terra cotta pots, let's explore some of the characteristics of these pots. To begin with, they are porous and will wick water away from the soil, where it will be exposed to air and evaporate. This is good for plants requiring excellent drainage, and for plants that like additional humidity. However, this also means that the soil will dry out quickly, so you'll need to water more frequently, and to ensure thorough saturation, you may want to immerse the pot in a larger container of water every few weeks during the hot summer months. Terra cotta pots can also absorb and radiate the sun's heat, which could turn it into an oven if it sits in hot summer sunshine. Be sure to group the pots together or set them behind a boulder or shrub or wall to help deflect the heat. A final characteristic of terra cotta is that it will eventually become discolored with mineral deposits unless they are coated inside with a waterproofing material. Some gardeners welcome this appearance; others don't. And, terra cotta pots can crack if they're exposed to freezing temperatures. Sealing the pots will remove the possibility of wicking the water away from the soil and will keep them from discoloring with age. So, the choice is yours. As for growing gardenia's, they love humidity and shade from hot afternoon sunshine. If you keep the soil moist but not soggy wet and irrigate the foliage each morning (mist with the hose), and feed every 3-4 weeks with an acidified fertilizer (such as Shultz's or Peter's), you should have success with your gardenias. Best wishes with your container garden!

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