Question
I got my orchid like 3 weeks ago, it's purple and I've been watering it about once a week, soaking the soil it's in and letting it drain, but about a week ago I noticed some roots turning black, and a white cottony substance (mold i think) growing on the soil and on the roots. What's wrong? What should I do?

Answer
Hello Austin,

If it is mold that is growing on your orchid soil, it may be due to the soil being kept too wet.  You did not mention where you live or what type of orchids you have but that may not matter in answering your question.  

Most orchids need to have the soil or potting media to slightly dry between waterings, kept almost constantly wet can lead to all kinds of problems such as media breaking down quickly, roots rotting due to lack of adequate air around them, fungus gnats setting up their home in the media, mold and algae growing on and within the media, etc.  

What to do?  First try not watering so often, wait until the potting media becomes barely moist before watering again.  As you begin water reduction, try smelling the media and if there is a sour odor present that would indicate the media has broken down and needs to be replace with fresh media.  If it smells okay, just work on the watering for now.  

There is a possibility that the white stuff you are seeing may be either mealybugs or boisduval scale, both can do quite a bit of harm to your orchid if left unchecked and allowed to increase in population.  Mealybugs have a white cottony looking covering over their bodies, touch them with a little isopropyl alcohol and the white stuff disappears, exposing their bodies.  Bosiduval scale have a hard shell over their bodies making it very difficult to get to them.  Either insect can be dealt with by the use of a systemic insecticide, go to your local garden center and ask for one that is recommended for orchids and use per directions and follow all safety precaustions.  

As for how to grow the orchid, I'd need to know what type of orchid it is and where you live to be able to offer some suggestions.  

Hope this helped you.  

Jim Kawasaki
San Jose, Ca.