Interbay Mulch

Monte(6-NE NJ)January 1, 2013

There has been much posted on the forums about a soil building method known as Interbay Mulch. It is a method developed by a site coordinator at the Interbay P-Patch in Seattle and has recently been featured in an article in Organic Gardening. The P-Patches are a large network of very well run Community Gardens. It is catching on quickly in other P-Patches but the folks at Interbay used the system for a full season before it started being adopted elsewhere.

The Interbay Mulch is the use of a layer of burlap placed over the top of various organic material that you pile up on top of soil. Organic matter decomposes much faster on top of the soil than it does if tilled in as long as it is covered and kept moist and dark. The byproducts of this process enrich and feed the soil under it in some very interesting ways.

A few years ago a four day course on soil ecology was held at Oregon State University. This course was attended by one of the Interbay site coordinators and the idea of Interbay Mulch occured to him while driving back to Seattle.

The OSU microarthropod expert, Dr. Andy Moldenke, said in his presentation that 90% of all soil organisms live in the top inch of the soil. Dr. Elaine Ingham of SoilFoodweb then said in her presentation that plant health and productivity depends on that biological activity in the soil. These two bits of information inspired the concept of using a burlap "cover" to create a deep,dark,and damp "litter layer".

The Interbay Mulch attempts to expand the conditions in that biologically active one inch litter layer to 6, 12, or even 18 inches. The idea is to recreate and magnify the natural conditions that produce rich, fertile soil. The use of damp burlap (coffee sacks are readily available in the Seattle area but purchased burlap can be substituted) proved to be the ideal material for enhancing the biological activity associated with the humus production.

Depending on your soil needs, and the amount of organic material you have access to, you would build a mulch 6" to 18" deep.

Mix the materials well and wet them down. Cover over this with the burlap. The burlap should also be damp. You could soak them in a large barrel (they will be HEAVY) or water over the "hump" with a sprinkler until everything is nice and damp. Monitor the pile for moisture content and water if any materials are dry. Decomposition comes to a halt when materials dry out. The mulch will probably be reduced to 30% it's original height when it is finished and will have turned into a rich, dark and most importantly biologicaly active humus.

The breakdown/decomposition time will vary depending on your zone and the time of year you build your mulch. Expect 4-6 months on average before you can move the burlap aside and plant.

This has been compared to a long-known method of soil building known as "sheet composting" and, more recently, "Lasagna" gardening. While there are similarities in these methods and some common benefits, the...

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