Weed Mat Discussion
In our first three systems, we put down a non-woven commercial grade weed mat PLUS a woven weed mat on top between the troughs before building the troughs, then covered it with 3″ of gravel. This solution was expensive, and weeds still came up through it. We spent hours and days pulling out weeds that had come up through the weed mat, and in the process made huge holes in the weed mat that made it easier for the next generation of weeds to get started and established in those holes. We were actually making it easier for the weeds; and we hate pulling weeds!
This motivated us somewhat to solve the weed problem when we built the systems, not later. As a result, we found a non-woven weed mat generically known as “geofabric” or “geotextile”, which is called Tencate Mirafi 180N (weight). This stuff is bulletproof, with tear strength of something like 600 pounds, and no weeds get through it, if you put a layer of 6-mil black construction plastic underneath it first. This is because weeds come right up through the stuff if you omit the black construction plastic.
If you can’t find the Tencate Mirafi, this type of material is generically known as geotextile or geofabric, so ask for that. It can be bought at landscaping suppliers, irrigation suppliers, and often from contracting suppliers. It’s generally used under parking lots and roads to stabilize the soil so the pavement doesn’t sink into the ground. Applying a layer of this material (plus the 6 mil plastic underneath it first) before construction of the troughs reduces weed problems without spraying anything, which would eliminate our valuable organic certification. If you want to pull weeds for the rest of your life around your aquaponics system, don’t put in weed mat, or just put in one layer of the thin stuff!
Oh yeah! We also “dust” the area under the weed mat first with a heavy layer (50 lbs per 500 sq ft) of Citric Acid. This is an organically-approved herbicide; if a weed seed does get under there somehow, this will greatly inhibit it from ever sprouting!
(Below) A photo of the approved types of Citric Acid and DE for use in organic aquaponics systems, along with a hand “seed spreader”, which works well to apply. WEAR A CARTRIDGE RESPIRATOR MASK WHEN YOU APPLY!!!
Oh yeah! We also also “dust” the area under the weed mat at the same time with a heavy layer (50 lbs per 500 sq ft) of Diatomaceoous Earth (DE). This is an organically-approved insecticide, it kills all kinds of hard-shelled bugs, including centipedes, ants, aphids, and others that will cause you problems. This will keep ants and other insects from conveniently making their homes under a food and water source (your aquaponic system!) Lots of info on how to use it in our Pest Control Category under Plants.
DANGER! Both of these are non-toxic if swallowed. BUT the Citric Acid will irritate your lungs incredibly, and the DE will give you Black Lung (silicosis, or coal-miner’s disease) if inhaled in large enough quantities. So make sure you wear an appropriate cartridge-filter breathing mask when you apply them and until you get the black 6-mil plastic down on top of them!