Bacteria and Mold

I received two emails recently regarding mold/bacteria on walls. Sam wrote:

"Hi Matthew,

My name is Sam, i'm from auckland NZ and we built a large green wall based off your video on you tube after reaching a lot of brick walls with landscape companies, so we decided to do it ourselves.

Our wall is progressing really well, the density is great, some plant types have not done so well, but almost all have survived, and thats about 1500 plants! The one issue we are having is smell. After 2 months, the felt we used has water in it of course, and has started to smell damp and musty. On invetsigataion with our hydroponics consultant he told us is was being caused by anaerobic bacteria in the felt. He advised us to use "waterclear" that is available that goes in the water system and kills the bacteria, and he has assured me that it is not only safe for the plants but it improves the oxygen available to them. So we have tried this and while not much has happened since we applied it, it is early days.

I was wondering if you had come across this or have any advice?

cheers"

I replied to Sam via email and asked him how often he was watering. If his wall is going through distinct wet/dry cycles I'd think the bacteria wouldn't really be an issue. Also it seems odd to me that anaerobic bacteria would be an issue with plants in synthetic felt as it is a fairly open material. Was this wall made with synthetic felt for it's moisture retention layer? Sam if you are out there please let me know more. Also I'd love to post pictures of your wall so please send them in.

Jared wrote in about mold growing on his wall:

"Hey,

First off I just wanted to say I love your blog. Without it I don't know if I would have gotten my greenwall up and running nearly as well. I'm having a problem, though, that I was hoping you might know a solution for. My wall has only been up for about 4 weeks, but a little over a week ago I noticed small amounts of mold growing on the felt material I used. I've been using a vinegar/water mixture to kill it, and it works without hurting my plants, but it only kills what has already grown, and doesn't prevent further growth once the vinegar is diluted. Do you have a safe solution that might work? I was considering moving my wall so it receives direct sunlight. I heard mold has a much harder time growing with enough sun.

My wall doesn't compare to yours, but I've attached a picture in case you wanted to see. It's a self-standing wall which is why I'm able to move it when I need to. It's not completely done yet. I'm a poor grad student so I'm adding plants little by little when I can spare the money. I'll be adding another 15 today actually. In the picture I'm sending only about half is covered so far. If your interested I can send you another picture once it is complete.

I hope to hear from you soon, and thanks again for your blog. It is amazing!
-Jared Brown"

I've never had a problem with mold on my wall. I'd be curious to know about your wet/dry cycles. How often are you watering; amount and length of time. What material did you use for your felt? Let me know in the comments please.

If you have any helpful suggestions for Sam or Jared please comment. I'm no expert when it comes to mold/bacteria so any and all help would be appreciated.

Thanks,

Matt

Great alternative to PVC suggested by Eric

Eric wrote:

Hi Matt,

This is a great blog, thank you for taking the time!
I have been searching the web for actual construction details to build a living wall.

A suggestion for basin construction. Use 45mil EPDM synthetic rubber membrane.
(To me this is the easy part ;)) I design and build ponds and waterfalls for a living.

EPDM is reusable, recyclable, and has better environmental impact profile than PVC. - See below

1) Build a basic plywood box in whatever shape and dimensions you need.

2)Calculate liner size L x W needed like so:

L x W
(length + 2x Height)X(width + 2x Height)

3)Line the box with 45 mil EPDM rubber, -folding it like a gift box in reverse it to fit the shape of your box.
3) Use a staple gun to attach liner to top edge of your box, and trim the edges with a blade or sharp scissors.

EPDM is available in custom cut sizes as pond liner for water gardens at many garden centers and is available on line at any pond supply place in 5 ft. increments.

*Ethylene propylene diene (EPDM) type rubber is recommended by the Danish Environmental Protection Authority as an alternative to PVC."
"Alternatives to dioxin sources in the Mediterranean," by Beverley Thorpe, Clean Production Action for Greenpeace Mediterranean Project (September 1996)
http://archive.greenpeace.org/toxics/reports/btf.html ( As found in Google Answers Answered By: mother-ga on 14 Jun 2002 14:30 PDT)

Thanks Eric and keep the basin suggestions coming. Readymades and materials suggestions are all welcome.