|I have a xanadu philodendron, in a semi-sunny position (in a restaurant). Some of the leaves are turning yellow. I have just fed it with slow release fertilizer. There are nw leaves growing. Is this a lack of a certain nutrient or something else?
|Lack of nutrients would generally show as an overall lack of vigor and the leaves turning a paler green, rather than yellowing. Generally speaking, as long as you read and followed the label instructions and used a fertilizer formulated for indoor foliage plants, then that should be fine.
Fertilizing is usually most important in spring and summer when the days are long and less needed in the fall and winter as the days shorten and the plant naturally slows its growth. In either case, it is better to underfertilize than to overfertilize. Overfertilizing can actually cause yellowing due to its potential "burning" effect if overapplied.
In my experience, an occasional yellowing leaf is somewhat normal for this plant. These should just be removed as they occur to tidy things up.
Extensive yellowing leaves, however, are most often caused by allowing the plant to dry out too much. This is an easy care plant but it does require regular attention. For best results, the soil should be kept evenly moist but not soaking wet. Make sure when you water that the water is soaling into the soil and not running out between a gap between the pot and the soil.
As the plant grows and the roots fill the container, you may need to water more often than you did earlier. Eventually, the plant may need watering so often that it may need to be repotted. The best time to do this is in spring, although it can be done anytime if a plant is severely rootbound.
General care would also include gently cleaning accumulated dust off of the leaves from time to time, either by wiping with a cloth dampened with plain water or by rinsing it under a soft spray of tepid water.
Other causes for yellowing can be exposure to hot or cold drafts, excessive direct sun reaching a plant that had previously been grown in a relatively dark location, and interestingly enough, overwatering.
If the soil is kept too wet the roots suffer lack of air. For this reason, do not allow the plant to sit in a saucer filled with water after watering, and try to keep it moist but never totally saturated. Sometimes, in offices for example, several people will independently water a plant with the best of intentions and the end result is overly wet soil. Maybe this is happening in your restaurant also.
Good luck with your plant!