I bought a Phalaenopsis orchid from the Paesaggistica nursery in Milan three months ago and it was fine until recently. Now the lower leaves are turning yellow and when I took it out of the pot I saw that the roots are black and smell like rot. I was watering it every two days because I'd read that orchids love humidity, but maybe I overdid it. What can I do to keep it from dying?
Unfortunately you've been watering too much! Phalaenopsis hate sitting in wet roots and every two days is way too frequent - usually 7 - 10 days between waterings is enough, depending on how fast the substrate dries out. You need to take it out of the pot right away, cut off all the black and rotted roots with sterile scissors, repot it in fresh bark (actual orchid bark, not regular soil!) and from now on only water when the substrate is almost completely dry, maybe by soaking the pot in water for 10 - 15 minutes. The yellow leaves probably won't turn green again but they won't drop off, and if you act fast the plant should bounce back!
Yes, excess water is the main problem, but at this point you need to act fast because rotted roots don't recover. Take the plant out of the pot, cut away all the black and mushy roots with disinfected scissors, and repot it in a substrate made specifically for orchids (fine bark, not regular soil). Then let it dry out well before watering again - wait at least a week and then only water once the substrate is completely dry, maybe by soaking the pot for a few minutes. The yellow leaves unfortunately won't turn green again, but if the healthy roots take hold, the plant should bounce back and grow new leaves. Oh, and put it somewhere bright but out of direct sun while it recovers.
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