By Larry Hodgson
Question: My girlfriend and I don’t share the same point of view on the use of landscape fabric in creating our new flower beds. I’m not a fan of it, because I have a feeling it will keep the plants from thriving. My thought is that a good layer of mulch with a bit of added hand-pulling ought to be enough to control the weeds. What do you think?
Answer: I have to agree with you … but you still need to convince your girlfriend. So, I’ve tried to build up an argument you can use to persuade her.
I tried this many years back: in the 1980s, when landscape fabric was a brand-new product. I prepared a new bed, installed the landscape fabric, cut out planting holes, dropped in plants, added mulch (bark nuggets, as they were the in-product at the time) and sat back, expecting to be amazed at the facility of maintaining this new-style low-maintenance garden. I wasn’t. I was horrified at the results! I pulled out the fabric and redid the garden before the end of the second year: it was clear to me that the plants hated this technique.
I now use something biodegradable to smother weeds (newspaper, cardboard, etc.) and a thick mulch to keep them from coming back, never landscape fabric.
What Is Landscape Fabric?
Let’s define the product more clearly so you can better understand what happens.
First, landscape fabric or weed barrier (both names are used) is generally sold in rolls. It is usually a type of agrotextile, typically made of woven or nonwoven plastic, and is usually black or gray, although I’ve seen other colors. It’s supposed to be very durable (some products offer a 25-year guarantee). The basic idea is to place it so that it covers the bare soil between desirable plants, cutting off all light to the soil below and therefore preventing weeds from growing. However, since it is permeable, it still allows air and water to penetrate, so your plants should do fine. Sounds great, right? Well, read on!
How Weed Barrier Is Used
Let’s now look at how landscape fabric is supposed to be used as a weed barrier.
Typically, landscape fabric is applied to the surface of a flower bed or around trees or shrubs. (It’s not used with annuals, vegetables or other plants that need to be frequently replanted.) The concept is simple enough: you just cover the entire bed with fabric, overlapping at the edges if the bed is wide, and cutting off any excess so that it follows the form of the garden. Then the fabric is pinned to the ground at regular intervals with pegs or staples to keep it in place.
(Do note that you need a lot of pegs or staples, as you’ll soon find that mulch alone simply doesn’t do the job. So many such gardens have bits of landscape fabric poking up out of the soil over time.)
To plant, you first cut an “X” in the fabric. This gives you four triangular panels you can fold back to access space for planting. The hole doesn’t have to be much larger than the plant’s root ball: the idea is to expose the least amount of soil possible so weeds have nowhere to grow.
Then you dig a planting hole, slip the root ball in and backfill with soil. Of course, you can add amendments if you want.
Next, fold the fabric triangles back around the plant leaving as little soil exposed as possible.
Since a flower bed covered with black landscape fabric would not be very attractive, you then cover it with a thick mulch that will hide it from view. The choice of mulch is up to you: people tend to use bark chips, shredded wood, pine needles or cedar mulch dyed in various colors. Others use ornamental stones or even rubber mulch.
Then repeat this method for all the other plants.
And there you go! You have a beautiful flower bed that is almost maintenance free, since the landscape fabric will prevent weeds trapped in the soil underneath from growing and weed seeds, already present in the soil underneath, from germinating. Extraordinary!
Except that this system doesn’t work like that for very long.
The problem is that plants seem to hate weed barriers. Perennials grow with a certain amount of vigor at first, but soon slow down and weaken. By the second year, many are dead or dying. Obviously, with plants weakened and dying, this leaves empty space for weeds to move into. Shrubs and trees tend hold on longer, but even their development gradually slows down. You often end up with a puny specimen with a lot of dead branches.
What’s going on? Several things, actually!
First, the soil fauna, mostly beneficial microbes such as algae, fungi and bacteria, but also other small creatures such as insects, other arthropods and earthworms, which are normally present in good soil and which participate in the mineralization and humification of dead organic matter, becomes depleted. Many species die or move because the soil is now less oxygenated and much drier than before. (True enough, landscape fabric is supposed to be permeable and theoretically allows air and rainwater to penetrate, but in fact, much less of both resources filter through than normal.) Plus, now there is less and less organic material (it can’t penetrate the fabric) and it is the organic matter that nourishes the fauna. The beneficial action of the soil fauna (aerating the soil and enriching it in organic matter) slows down.
This combination of limitations—less air, less water, less organic matter and fewer beneficial microbes—also, of course, harms plant roots. The vigor of the plants decreases, especially in the case of plants that prefer rich, moist soil … the situation with most garden plants.
Also, plants can no longer expand in width to any degree, as they are surrounded by the landscape fabric that now acts as a barrier to their lateral growth. For plants that normally expand in width over time by dividing at the base, like most perennials, this accelerates dieback.
And the situation gets worse over time, as particles of soil, blown in by the wind, filter through the mulch and accumulate on the surface of the fabric. It is really surprising how quickly a new layer of soil forms on top of the fabric. In 2 or 3 years, there can easily be half an inch (1 cm) or more.
Particles of soil also begin to clog the pores in the flower bed, further reducing the flow of water, air and organic matter to the roots.
But that’s not as striking as the return of the weeds.
Yes, new weeds, coming either from seeds brought by the wind or dropped by birds or animals or by rhizomes wandering in from neighboring plantings, settle in the new layer of soil above the fabric, then root into it. Yes, their roots manage to grow into and through the fabric’s pores. And, of course, now solidly fixed to the landscape fabric, those weeds become almost impossible to remove.
Thus, if at the beginning (for a year or so), landscape fabric suppresses weeds, they come back over time … and are more difficult than ever to control!
What to Do?
If you decide to tear out the landscape fabric (and few people tolerate the mess it creates for more than a few years), you’ll find that this is very difficult to do, because the roots of any desired plants that are still alive have likely rooted into the fabric from below, making it hard to remove without damaging them, while weeds that rooted in from above also help hold it in place.
And what can you do with the used fabric when you do get it out? Landscape fabric is made of plastic (usually polypropylene) and therefore theoretically recyclable, but since it is now filled with roots and soil, even recycling is no longer possible. It will have to go directly to the trash … or rather to the nearest waste collection center.
Other Uses of Landscape Fabric
Obviously, the comments above only apply to using landscape fabric on the surface of soil as a weed suppressant for flower beds and other plantings, that is, covering the roots systems of living plants. This product has many, many other uses in landscaping—you can place it under a path to keep rhizomes out, in a water garden to protect the liner, under a deck to suppress weeds, around a drain as a filter, etc.—, all situations where you would never want to see plants growing. So, it’s not that landscape fabric can’t be very useful, but it just doesn’t work at all well when you use it in conjunction living plants that you want to maintain. I simply wouldn’t recommend its use as a weed barrier for gardens, at least, not if you want good long-term results.
Think of it this way: landscape fabrics and garden plants are essentially incompatible!