Question
I have a white fuzzy substance on the earth as well as a green mildew like one.  It is not on the plant.  The plant is a large 4 season cactus. The earth was changed a few years ago. How can I get rid of this?

Answer
Hi Mona,

From your description, it seems that there are least two types of fungus growing in the soil.

I do not know what you mean by "4 season" cactus. However, it is very unusual for fungus to take hold in Cactus soil. That is because Cactus soil is very sandy and because Cactus soil should dry out completely in between waterings. Sandy soil that is low in humus and that gets completely dry is not conducive to the growth of mold.

Without knowing exactly what plant you have or anything about the light and water you provide, I suspect that your Cactus is in the wrong kind of soil and that it is staying too wet. If so, then the roots may be rotting or already rotted and that will kill the plant. The fungus will not harm the plant, but it is an indication that the soil is staying too wet.

For starters, try scraping off all of the visible mold from the surface along with and loose surrounding soil. Then let the soil dry out completely to the bottom of the pot between waterings.

In addition, most Cacti prefer to be in direct sun and sunlight is also a deterrent to mold growth.

Please let me know if any of this is unclear or if you have any additional questions.

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If you would like to e-mail me some photos, I may be able to provide some additional insights.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

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