Answer: The most likely culprit is the buildup of soluble salts within your soil. Soluble salts are minerals dissolved in water. Fertilizer dissolved in water becomes a soluble salt. Not only will soluble salt buildup result in a crusty often white or yellow buildup on your clay pots, it will probably eventually damage the plants as well. The best way to prevent this problem is to be careful with your watering and fertilizing. When you water, allow some water to drain through the drainage hole and then empty the drip plate. Water equal to 1/10 the volume of the pot should drain through each time you water. Never allow the pot to sit in the water. Also, plants should be "leached" every 4-6 months. Leaching is done by pouring a lot of water into the soil and letting it drain off completely. Use twice the amount of water as the volume of the pot. For example, a 6" pot holds 10 cups of water so you would use 20 cups of water. Watch fertilization also. The general rule of application is to fertilize every 2 wks. from March to September; you can use a 20-20-20 fertilizer. Or use an organic fertilize. No fertilizer is needed during the winter months because reduced light and temperature mean reduced growth. All of this may prevent the crusty buildup in the future. For now, you will need to scrub it off...or, you could use plastic terra cotta colored pots.
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