pebble tray maintenance re mold

WendyB(5A/MA)September 8, 2008

I grow houseplants on a etagere setup with flourescent lights and metal trays less than 1" deep with pebbles that are just barely covered with water. I think the setup is nearly 2 years old. The pebbles were shiny small decorative river rock. The shine is now gone.

When I first set it up, I threw in some charcoal bits in the pebbles to help keep the water clean. Not sure if that had any affect. About 6 months or so ago, I noticed some dark areas on the pebbles, likely mold. I added more charcoal and sprayed with bleach and water.

Now I see a white dust-like film which I suspect is more mold.

I am wondering if there is something else I can be doing to avoid these problems?

Or just keep spraying with bleach as needed. Or cleaning them periodically (disassemble everything and rinse the trays and pebbles in bleach/water.)

I am a concerned that adding bleach to the humidity water could wick up to plants root systems or even generate foliar absorption??? I usually use pot saucers on the individual plants, but not always.

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maineman(z5a ME)


I suggest you take a look at Physan 20.


    Bookmark   September 11, 2008 at 10:13PM
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The white dust could also be deposits from the mineral content of the water.

I'd say to strip it all down regularly, say like 2-4 times a year according to how much it needs it, and just thoroughly clean everything.

Definitely do a 10% bleach solution to kill whatever crud might want to grow in there. I'm not sure on the rocks what would bring back the shine the best. You might need to CLR them or something like that.

Just make sure you thoroughly rinse everything afterwards. Rinse it till you're sure it's clean, then rinse some more. (Let it soak in a big bucket or something overnight, then rinse again.)

Once everything is nice and new looking again, just clean it whenever the luster seems to be dulling and it shouldn't be hard. Just a couple hours soak in bleach water, a few hours in clean water, and you're done.

    Bookmark   September 25, 2008 at 11:12PM
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Thanks for the ideas. mineral deposits is possible. I hadn't thought of that. It did kinda look like the white layer that clay pots get. I clean those pots in a vinegar solution with some bleach for good measure.

Until I get a chance to dissassemble and clean well, I haven't been filling the trays with water. I've just been misting the plants more often.

I was thinking that after they are washed and dried, applying a spray of polyurethene to bring the shine back. That could be what was on there in the first place. If so, makes sense that it would wear off.


    Bookmark   September 26, 2008 at 11:25AM
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If I interpret correctly, you have stagnant water. I don't recommend stagnant water. Drain off and discard runoff water, automatically by gravity.

    Bookmark   September 26, 2008 at 4:14PM
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Let me know how it goes, Wendy. If you have any problems or run into any hitches I'll be happy to lend my brain for what it's worth.

lermer makes a good point on the stagnant water - it's always best to avoid it but if you haven't had a major problem so far I'd have to guess it's not likely to cause you one.

    Bookmark   October 4, 2008 at 2:15AM
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I don't understand the stagnant water point... what about:

for humidity grow on a pebble tray with water

isn't that always going to be stagnant water?

Stagnant water reminds me of mosquito larvae opportunities outdoors.

this is a 4' x 1' long 1" high tray covered with pebbles and plants and with cords and lights on its underside. tipping it to discard runoff water is not an option.

    Bookmark   October 4, 2008 at 7:43AM
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Stagnant water causes a number of different problems, but the point I was trying to make earlier is that if you haven't had any obvious problems so far you probably don't have much to worry about. Just keep an eye on it.

Stagnant water can attract insects (mosquitoes, various flies, and so on) as well as be a great environment for various molds, fungi, and bacteria. Those tend to be the biggest problem in hydroponics, but can also be really annoying anywhere else. A common by-product is a lot of stink and/or allergy problems.

An easy fix is to just add some hydrogen peroxide to the water whenever there's a problem, or even as a preventative. (Same reason hydroponics systems aerate the water - oxygen is bad for the bad stuff.) It breaks down harmlessly into oxygen (the bubbles) and water, and helps keep the water from looking inviting to the nasty things that want to grow in it.

    Bookmark   October 9, 2008 at 2:02PM
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