The average homeowner chases after the elusive “low maintenance, so I can watch more Netflix” landscape, and the residential landscape industry has happily obliged with a barrage of products. One great example is the use of some sort of physical weed barrier to rob those pesky germinating seeds from having a way to the surface to gather the much needed sunshine. Sounds good, eh?
Physical weed barriers come in an array of materials, from no frills sheet plastic to woven cloth or recycled materials. Like many things, you can find enthusiastic support as well as extreme disdain for the stuff. I think the truth is somewhere in between. Landscape fabric (I won’t call it weed barrier again) has its utility for the right application, serving as one tool in a land manager’s box of tools.
First, let me address what I consider to be a misnomer. Fabric is not really much of a barrier to weeds in the long run, and it causes more harm than good in the average aesthetic planting bed. “Weed barrier” is most often used in combination with herbicides, both pre- and post-emergent, as a two prong management system to prevent the spread of weeds in those wide gaps between plants conveniently left by the homeowner or landscape crew. Those nicely spaced plants leave LOTS of room for nature to add its touch of class to the bed. This two pronged attack on weeds really creates more work long-term, creating a bed system often with more problems than solved including increased nutritional and disease issues. Why is this the case? The answer is simple: soil health.
Landscape fabrics deployed to suppress weeds may have a long-term negative impact on the health of the garden soil. First, the physical barrier prevents the normal mixing of the organic layer at the surface with the soil beneath. There is no barrier in nature, so the duff breaks down and is naturally incorporated into the soil. As a matter of fact, what separates barren rock from “soil” are the organic matter and organisms living amongst the mineral content. Solid plastic sheeting does additional harm by preventing the exchange of moisture and gases vital for good root and soil health. Plastic landscape barriers should never be used, in my opinion. Woven fabrics do allow water and gas exchange to some degree, however, they, like plastic sheeting, encourage compaction at the soil/fabric interface over time. Thus, the rate of water and air exchange decreases over time, creating poor soils. Poor soils means poor plants which are increasingly dependent on the homeowner for their every need, not just protection from competition. Increased inputs on your part means increased costs. Put fabric down, and you can no longer feed the soil with organic amendments.
Reason number two I discourage the use of landscape fabric in the average flower bed is it does not eliminate the problem, hence the additional use of chemical methods. Fabric does often REDUCE the weed population in a bed for the first season or two, but as soon as you introduce any kind of mulch (organic or rock) on top, you just provide an environment for weeds to germinate anyways, hence the need for chemical reinforcements.
The third reason I discourage the use of fabric is it becomes more work. If you want to add or subtract plants, change things up, the fabric presents a challenge. Working with fabric when planting is a bit of pain, and the more you punch holes in the fabric, the more you destroy the integrity of the barrier against weeds. If you have herbaceous perennials or multi-stemmed shrubs at all in the bed, it restricts their growth, their natural annual expansion (this is less of an issue for trees and single stem shrubs). Landscape fabric in this environment assumes the flower bed remains static, denying the reality of the ever changing, evolving nature of a garden.
“Fine,” you say, “I love the earth. I do not use such horrible man-made products. Never in my yard! Captain-plant gives me a green check mark every year. I use plant fiber based weed barriers like newspaper or cardboard. It breaks down and is organic.” I have some sad news for you. In an average flower bed, newspaper and cardboard mulches have all the same drawbacks listed above. In a vegetable garden, the situation is different, however, where the soil is kept moist and turned more frequently, encouraging the breakdown of the plant fiber. The infrequent moisture event and soil turning, by comparison, of a perennial bed does not break down plant fiber products very quickly.
Does this mean there are no pros for the use of weed barrier of any ilk? No, there are some pros and some appropriate uses of fabrics. We use fabrics and plastic sheeting here at Wellfield in two situations. Soil stabilization is the first Wellfield application of fabric. We place fabric behind most of our retaining wall construction (block or boulder) as a means of preventing soil movement/shifts behind the wall over time. The second appropriate use is under rock mulch, preventing the rock from sinking into the subsoil over time, but since I am not a big fan of rock mulch (another blog post for another time), we have not done this here. The second use of “weed” barrier is in the initial suppression of weeds. We temporarily use black plastic on our Quilt Garden bed every spring as a means of killing the cover crop prior to planting annuals. It is laid down for a month and then removed.
No matter how you cover the subject, nothing replaces good old organic mulches and careful plant spacing, among other organic design tools, to manage your “weed” problem. It is usually less work and cost in the long-run – and I like less work and cost, don’t you?
Josh Steffen, Horticulture and Facilities Manager
Missed any of Josh’s latest posts? Click below to read more:
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