Problems with Overwatering
Nun's orchid grows best when its top 2 inches of soil dry before the soil is watered. Otherwise, soggy conditions can prevent aeration for the roots, increasing the likelihood of rot. You also may notice symptoms on other parts of the orchid, such as slowed growth and wilting leaves. Those symptoms occur when roots become so soggy they begin to die. Dying, they are unable to take up the water and nutrients the orchid needs to thrive.
Sometimes judging whether or not a nun's orchid is overwatered is difficult because the top of its soil may be dry but soil lower in its pot may be overly moist. In that situation, its roots -- especially the lowest ones -- can become soggy, rot and eventually die if the wet condition isn't remedied quickly. Check whether or not a nun's orchid is overwatered despite the top of its soil being dry by picking up its pot to judge its weight; wet soil makes a pot heavier than dry soil. Also feel for moisture inside the pot's bottom holes.
Remedy for Rotting Roots
If your nun's orchid suffers from soggy roots, repotting it in fresh soil is the smartest remedy. Although a nun's orchid grows in regular soil, it grows better when materials such as peat moss and bark chips were worked into its soil at a rate of up to 70 percent. After its flowers fade, gently shake your nun's orchid free of its potting soil, and snip off roots that are brown and soggy, leaving only pale, firm roots. Repot the orchid in a pot filled with sterile potting materials, such as a mixture of soil and peat moss.
Improvement of Soil Drainage
Water should drain out the bottom of a nun's orchid's pot, a process that requires holes in the pot's bottom and well-drained soil. The drainage holes and well-drained soil will prevent soggy roots. At planting time, working organic matter, such as peat moss and decomposed pine bark, into the soil keeps it rich and aerated. Afterward, add sand and perlite to soil to make it more porous. In addition to improving the speed of drainage, porous soil also allows oxygen to reach roots and prevent rot.