Carnivorous Plants/humic acid and sundews
I'm having this ongoing issue with my Alice sundews and Spoonleaf sundews that involves the buildup of the brownish substance on the new leafs of the plants which causes them to become deformed, this substance can be wiped away though with a wet paper towel or cloth. There doesn't seem to be any sign of pests that would be causing this. I read on a site http://www.growsundews.com/sundews/Sundew_Problems_Page-Drosera_help_recovery_an
that the cause may be humic acid in the peat that forms a crust on new growth causing them to deform. I'm not sure what to do on this since I've been top watering to leach out the acid and wiping the substance off the new growth, yet to no avail as it is back the next day. My plants are under grow lights as I don't have a window that receives sufficient sun during the day. All my other sundews in the same tray seem to be doing well with the light their getting so I don't think this is a contributing factor with my Spoonleaf and Alice sundews. I fill the water tray a quarter to a third of the way up the pots. So is this a humic acid problem or could it be something else and what can I do to correct the problem?
Without a photograph, I will have to rely solely on your description. This is OK, but many people have different ideas of "deformation." I will assume that you mean the brown substance on the center portion of the sundew. I've never referred to it as humic acid since that's what helps define peat moss as peat moss. Without it, peat moss wouldn't be peat moss. So I refer to that brown substance as peat moss particulates. (Technically, humic acid is a group of decomposed organic material and not a single substance.)
Yes, rosetted sundews are prone to this effect. I've seen it on D. venusta too. It's not a major problem to the overall health of the plant. If anything, it's a cosmetic issue. We tend to see it mostly during the winter months when growth is slower and there is less evaporation in the soil. Hence, the peat particulates accumulate on the growing area via capillary action along the fine hairs on the plant.
You can prevent this from happening by reducing the water level. You mention keeping it about a third of the way up. During the winter months, we actually recommend no more than a quarter of the way up. Don't add more water until the water tray is dry and the top of the soil is losing its dampness. You can also put your plants in taller pots, which has similar effects as keeping the water level low.
During the summer months, this problem tends to be less of an issue because of rapid growth and quicker evaporation.