Question
When I repot one of my carnivorous plants, usually Drosera, I almost always seem to end up with an unwanted algal growth on the surrounding potting medium. It looks like a scum, very dark green, almost black, that gradually grows across the entire top surface of the potting medium, sometimes even up the sides of the repotted Drosera plant. This also happens with my fly traps.

Questions: Is this algae harmful, or just unsightly? What is the best way to get rid of it? Is there a chemical solution that would kill the algae but not harm the plant? Or do I have to keep scraping it off, which is my only resort now?

Thanks in advance.

Answer
Hi Ted,

Mostly it is just a nuisance.  It can be a problem with very small plants or seedlings but otherwise it's just ugly.

Once you have plants planted, just scraping it off is your only option.  Chemical options would kill your plants too.

Before you plant, however, there are some options.  I've often poured boiling water on the soil surface to kill algae and fungal spores before planting.  I always do this before planting seeds otherwise algae and moss always take over too soon.  There are also some quanternary ammonium compounds that you can spray on the soil before planting that will kill spores.  These are essentially disinfectants.  You would treat, wait 24 hours, then plant.  Here's an example:  http://www.amazon.com/Orchids-R-Us-Inc-Physan/dp/B000I2UTAQ/ref=pd_sim_sbs_lg_1  

One other option is to give your soil media a soak and rinse before using it.  You would mix the soil up, saturate it with water, let it sit for a few hours, squeeze the water out, rehydrate and use it.  Doing that helps get rid of excess organics in the peat that the algae are using for food.

Hope this helps.

Good Growing!

Jeff Dallas
Sarracenia Northwest
http://www.cobraplant.com