I was working at a site that had been overrun by weeds. They completely invaded the landscape beds. And yet, those very beds had a weed suppressing landscape fabric installed. Seeing the absolute mess and the management strategies that led to it has motivated me to share some pros & cons about the use of landscape fabric.
Should you use landscape fabric? What causes it to fail? Are there any alternatives to a synthetic weed barrier? What should be considered as a long term solution?
Landscape or weed fabrics create an impassible barrier that stops the upwards growth of plants from underneath. So the soft stems and leaves get trapped beneath. When used in a home landscape though, an application of mulch is commonly placed on top. The mulch holds the fabric in place, blocks out the sunlight and further suppresses growth. Aesthetically, it looks nice. And as a short term solution for reclaiming a weedy bed, the fabric can help out.
WHEN LANDSCAPE FABRICS MAKE SENSE:
By its very design, landscape fabric is intended to last for a long time. It is made from non-degradable, synthetic fibers. So it works best when paired with mulches that will hold up just as well. Rubber mulches*, river rock or other stones. These materials won't decompose and turn into soil. But they WILL start to sink down into the dirt of your bed.
By adding a non-degrading layer to separate the soil from the stones or rubber mulches, you can set up a system that will last for quite some time. Of course, you need to keep the beds free from debris such as leaves. Failure to do so will result in the slow break down of organic matter which creates a soil in between the crevices of your mulches. Weed seeds blow in. And you have a weed infested mess.
It's not my personal approach to landscaping, but when used in this way, landscape fabric makes sense. It serves the same role as sheets of plastic would. But fabric at least has the added advantage of water permeability. Some of the rain falling onto your bed will penetrate and sink down into the ground. In contrast, a plastic barrier results in complete run off of precipitation.
* RUBBER MULCHES: I strongly advise against this material in most situations. Rubber mulch pieces can be lightweight and small enough to blow around in strong winds or to get washed out in heavy rains. Wood mulches have this same issue. But wood is naturally biodegradable and will break down, enhancing your soil. Rubber is not. It will always be there, becoming a liability, even after you've finally decided you don't want it anymore.
Worst of all, rubber mulches are highly flammable, much more so than wood. With the rise in wildfires across our globe, rubber mulches just make things worse, increasing risk to our homes.
DISADVANTAGES OF LANDSCAPE FABRIC:
Synthetic weed barriers can accomplish a task, but they're no silver bullet. When paired with the wrong mulch material, their limitations might not become apparent until a year or two has passed. But before long, you may start to see that your beds are just as weedy as they were before, especially if they've been neglected.
In many residences, wood based mulches are customarily applied on top of fabric. But the biodegradable nature of wood causes the mulch to slowly break down, forming a layer of soil. That upper layer can be a perfect rooting medium for fresh weed seeds that find their way into your beds. Before you know it, you've circumvented your weed barrier and weeds just grow right on top of it!
All the while the microbial processes that rejuvenate your soil are being hindered by this synthetic, barrier. Earthworms and various arthropods cannot freely pass from below the soil up to the surface.
Your perennial plants become girdled as they grow wider and wider. Clumping and rhizomatous plants get trapped underneath. And creeping or layering plants cannot properly root as their roots get entangled in the fabric.
Video: Landscape Fabric Finding an Alternative
A BIODEGRADABLE ALTERNATIVE:
A free, biodegradable alternative to landscape fabric is to use simple old cardboard. The idea is derived from the concept of sheet mulching. In permaculture, sheet mulching can be done to reclaim an area of land that might have been weedy or even covered with grass.
NOTE: Technically 'cardboard' is not the same as 'corrugated fiberboard'. Corrugated fiberboard has several layers sandwiched together which may include cardboard. But both materials can be used in this application and people often refer to both materials simply as "cardboard". So be aware that these can vary greatly in their thickness and number of layers.
Cardboard is applied to the area. Then a layer of mulch goes on top of that. In creating a highly fertile site, a gardener may put several layers of materials. Leaves, compost, grass clippings, straw, etc. But in more conventional landscape applications, it would certainly work to just put a wood based mulch right on top of a couple layers of cardboard.
Most weeds or grasses are unable to pass up through the cardboard. By adding wood mulch on top, you can effectively smother these unwanted plants, making way for new plantings. It's a great way to reclaim the bed and get a fresh start. Meanwhile, that cardboard breaks down and is eaten up by earthworms. Ultimately, it won't interfere with biological processes.
HOW LONG DOES IT LAST? This process is a temporary solution, not a permanent fix. The big advantage to cardboard is that it doesn't stay there forever, getting locked up in soil layers. I've seen the cardboard disintegrate after 6 months. But in other spots it's still been there a year later.
Several factors impact the decay rate. How thick is the cardboard? How many layers did you use? How thick was the top mulch layer? Is your area arid, or do you get a lot of precipitation? Dry cardboard may just sit there, lasting a long time. If it stays moist most of the time, it will break down much faster. Try to consider these factors when deciding if it's a good fit for you!
TIPS FOR SUCCESS:
PAIR IT WITH THE RIGHT MULCH: If you want to work with a wooden mulch, then cardboard is a great option. But it isn't a good barrier for use under stones or rubber mulches. It would work for initial suppression. But afterwards, the cardboard would decompose while the mulches would remain intact, slowly sinking into the dirt of your bed.
USE A THICK LAYER: Some people mention using newspaper as an option. It's a great way to manage weeds on your regular garden beds. To suppress a weedy or grassy patch, you would need multiple layers and a substantial mulch application placed on top. I prefer cardboard in landscape beds, using 2 layers (standard thickness). A single layer should work well if it's extra thick.
CARDBOARD PREP: Look for non-glossy cardboard that has a minimal amount of ink imprint. Select the largest pieces you can possibly get. Local businesses might allow you to dumpster dive for their cardboard. But I seem to always have some from various online orders. Pull off any staples, tape or stickers, since these won't decompose. Well established, vigorous plants may send their stems along the bottom, seeking an edge or a hole in your barrier. So when you need to use multiple layers, be sure to generously overlap the seams. It's also a good idea to pull out or dig up weeds that are at the very edge of the bed.
IT'S NOT BULLET PROOF: Worms enjoy soft, decomposing cardboard. Birds enjoy worms. So be aware that you may have animals perforating your sheet mulch layer. This might require weeding out any plants that find their way to the light. Besides pulling out those weedy culprits, you can always apply a quick patch. Just pull away the mulch and drop down a fresh layer of cardboard.
LONG TERM STRATEGY:
Are you looking for a way to reduce mulching requirements? How can you keep out weeds? Nature abhors a vacuum. So your final landscape or garden should be designed in a way that fills those large empty spaces.
Plan out multiple layers of trees, bushes, shrubs and herbal plants. Allow these to fill in your beds, choking out any weeds that make their way into your property. To cover large areas of ground, without relying on grass, consider using ground covers.
WHAT ABOUT TERMITES?
It's worth noting that cardboard is composed of cellulose. Thus, as with any other wood based product, it can serve as a food source for termites. If you have an issue with termites on your property then you might prefer to avoid making things worse by laying down cardboard. However, if this is the case, then there is more to do than simply avoid cardboard.
THINGS TO AVOID: To reduce feeding sources for termites, it's best to avoid all wood mulches and chips. That includes ones that might seem to be termite resistant like cypress or cedar. Eventually, the protective compounds in the wood will leach away and termites might feed on the wood particles.
Do not allow any wood to be in contact with the ground. Think about stacks of firewood. What about wooden boards used for raised beds? Even treated wood becomes vulnerable over time. Obviously you would not create any hügelkultur mounds which are comprised of logs that are buried under layers of soil.
CONSIDER THE SOURCE: In reality, termites serve a vital function in our ecosystems. Once a tree or woody shrub dies, termite colonies move in to break down the massive networks of buried roots. So if you are afraid of attracting termites to your property, then you might think twice about cutting down any trees or large shrubs on your lot. That is where the real termite invitation comes into play. A single medium tree will have deposited much more cellulose under ground than those few sheets of cardboard that you are contemplating.
PROTECT YOUR HOME: Perhaps you've cut down trees, applied wooden mulch or placed sources of cellulose throughout your property. Even still, there are certain basics that can be done to protect your structures from termite invasion. Essentially, you want to avoid creating any bridge from the outside soil to your home.
Subterranean termites feed on the extensive network of roots from dead trees. They will follow the path of wood or moist soil in search of food. So your buildings need to be surrounded by a buffer, a barrier of dry, uninviting soil. Make sure your ground is properly graded, sloping away from the base of your structures. Gutters and downspouts should be moving rainwater away from the foundation so that it is kept dry.
Don't lay cardboard along the surrounding perimeter. But don't use landscape fabric or plastic either. The soil should be kept bone dry to inhibit the migration of termites. That means no wooden mulch or chips, but also no rubber mulch or stones. Keep all of these things 12 inches away from your buildings so that there is only exposed, dry soil.
SOURCE: Subterranean Termites - a Handbook for Homeowners