Question
I read an answer to Mattie regarding mold on house plants.  I am wondering what exact action the charcoal would have.  I am careful to water my plants from the bottom to keep the top dirt from getting wet, but sometimes not careful enough.  (I live on the West coast of Canada- mold is quite an issue much of the year) I thought I might remove the top 1/4 inch of soil and replace it with clean sand or perlite.  Do you think that is a good idea?

Answer
Hi Jennie,
  I am not quite sure what answer you are referring to concerning charcoal.

Really the best way to deal with mold on top of the soil is to spray the top of the soil with an anti-fungal spray like Consan 20 or Lysol spray when mold appears on the soil.
I usually remove the top 1 inch of soil, spray the top of the remaining soil with an anti-fungal spray (I use Consan 20) and then replace the 1 inch of soil removed with fresh potting soil.

Good watering practices is a big part of mold control. I usually recommend top watering. With bottom watering it is too easy to overwater plants and to keep the soil too moist all the time. Also allow the top 1-2 inches of soil to dry between watering. That can go a long way in preventing mold.

I don't recommend putting sand or anything else on top of the soil. I have found that most of the time all a topping on the soil does is hold excess moisture in the rest of the soil.

Make sure you are using a good, well draining soil. I usually add extra perlite and sometimes vermiculite to a commercial potting soil to increase drainage and aeration in the soil.

So using a well draining soil, allowing the top 1-2 inches of soil to dry between watering and using a anti-fungal spray like Lysol or Consan 20 should be enough to keep mold under control.

By the way, the mold that usually grows on top of the soil doesn't harm the plants. Except in cases of 'damping off' disease in seedlings. The mold that causes 'damping off' disease is harmful only to tender seedlings and does not harm older, stronger plants.

I hope this helps. If you have any questions or need additional information please don't hesitate to ask.
     Thanks
       Tracy