Yuccas are sturdy, adaptable plants that usually grow without a hitch, but occasionally, yellowing leaves signify that something is amiss. There can be a number of reasons why the leaves of a yucca plant turn yellow, and it can often be a matter of trial and error to determine the exact cause. However, there are several possible (and easily-remedied) problems that, once addressed, can return your yucca plant to its former green glory.
Water the yucca plant properly, as over-watering and under-watering can both cause yellowing of the leaves. Water the plant until water runs through the drainage hole. Don't water again until the top of the soil feels dry to the touch. Immediately pour out any water remaining in the bottom of the pot. Allow the water to sit overnight before watering the yucca plants, so that salts and minerals have time to dissipate.
Check to see if the yucca plant is root-bound, as crowded roots can also cause the plant's leaves to turn yellow. If you see white roots growing through the bottom of the pot or on the top of the soil, there's a good possibility that the plant should be repotted. Another sign is tightly compacted soil that won't absorb water. To repot a yucca, use a container just one size larger. Be sure the container has bottom drainage. Fill the container with a commercial potting mixture that drains well, such as a potting mixture for cactus plants. You can also make your own mixture of two parts coarse sand, two parts peat moss, two parts commercial potting soil and one part perlite.
Place yucca in full sunlight. Lack of sunlight can be one reason for yellowing leaves.
Feed the yucca plant a balanced liquid fertiliser for houseplants every other month during spring and summer. Avoid fertilising yucca during fall and winter.
Keep yucca in a room where the daytime temperature are between 22.2 and 27.8 degrees Celsius, and about -12.2 degrees C lower during the nighttime, as sudden temperature changes can cause the leaves to turn yellow. Avoid sudden temperature changes. Don't place yucca near draughty doors or windows, air conditioners, heating vents or warm appliances.
Remove dead and yellow leaves from the yucca plant, and dispose of the leaves in the garbage. Keep healthy yucca leaves clean by dusting them occasionally with a soft cloth. Dust will block sunlight and air from entering the leaves.