First, some context: From observations I've made at various fields and garden beds, I very much buy into the concept of "aromatic pest confusers" (APCs) described in Jacke and Toensmeier's Edible Forest Gardens. I'm actually interested a bit in the idea as a pest preventative measure in more annual garden beds, as I'm not that concerned about pest pressure around many of my perennials (they don't seem to have a lot so far), and so I've decided to plant low-growing/mowable aromatic herbs between my beds as pathways. Although some of them are quite a bit aggressive (oregano and a couple varieties of mint), I'm not too concerned about spread because 1) I'll be mowing them probably once a week during peak season, which seems to really slow down rhizome expansion as plants attempt to recover lost growth; 2) I'm going to finally experiment with double digging, so that should disrupt rhizome growth into my growing beds as well; and 3) worst comes to worst and things go crazy, I'll just have to smother things under cardboard/sheet mulch for a few years – there are worse things in this world, and it was worth experimenting.
That being said, I do want to take good preventative steps if possible. I've been put off by a lot of the technical solutions people have proposed, because (and I'm not sure if folks are just being overly dramatic) even the most rigorous options like 12" deep overlapping rhizome barriers are described as ultimately not very effective and prone to eventual failure. My hunch is that it would take a long time for something like mint to get around such a stiff barrier, but there are enough hyperbolic horror stories out there that it concerns me. (Aside: has anyone ever considered soldering the seams of metal rhizome barrier with food-grade silver solder, or something similar? Seems like that would be pretty impenetrable).
Anyway, all of this lead to my eventual question: We tend to discuss soil compaction as something to overcome and have developed lots of techniques to break it up. Has there ever been discussion of using very focused, narrow bands of compactions as a sort of "natural" barrier? For example, the mint I'm planting likes lofty, garden bed soil and I've read that it has quite a difficult time expanding into compacted soils. I've never seen it taking over (or even doing relatively well) in abandoned lots that are filled with heavily compacted soils. My thought was that if I could find a tool like a vibratory compactor that I could tamp along the edges of the walkways, I could make a sort of compaction barrier and have very easy to manage APC walkways, while being able to keep the bed areas themselves lofted and healthy. Because I don't know much about how compaction is distributed or how persistent it is, I wanted to throw this idea out to all of you other permies! Would the bed prep I do ultimately undermine the compaction of the walkways (e.g. I've read about compost's and soil microbiota's ability to repair compact soils)? Would it even be effective, or are aggressive rhizomes tough enough to break through even deliberately compacted soil?
Compacted soil actually waits on primary succession plant seeds to arrive, this is one of the places they do their best work.
Purposely compacting soil will work for greatly used pathways since you will be using them most of the time, this means there will be fairly constant abrasion of any plants that try to become established there.
One of the best examples of what to expect is to find a dirt road, the tire tracks are where the most abrasion occurs on a regular basis with the area between the tires getting no or little abrasion.
About "barriers" most people never make them deep enough. When roots hit one of these barriers they have three choices, go over it (turn up to the sky), go through it (snake along until they find a crack(opening)), go down and under it (roots and rhizomes can go down around 3.5 to 5 feet deep when turned down by a barrier), once the root/ rhizome finds the end of the barrier they will go under it and escape to the "wild". One of the best examples of these events is running bamboo, barriers are recommended to be placed to 6 feet deep and with 8" or more above soil level. 1.4 inch thick PVC or ABS material is also recommended with glue welded seams.
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