Mulching is a simple solution to one of the most difficult problems in the garden—weeds.
But there are so many types of mulch, from landscape fabric to wood chips, leaves, and even cardboard. Which is the best to control grass and weeds?
The best way to inhibit weed growth is to use at least 6 inches (15 cm) of natural mulch (e.g. gravel) with some maintenance. Wood chips are the best organic option but need replacement every year. Landscape fabric and plastic mulch are not good because roots can still grow through and they are not breathable and are thus bad for the soil.
Check out our comparison of the 11 types of mulch to find out the best and worst ones to prevent weeds.
1. Will grass grow through landscape fabric?
Landscape fabric is not an effective solution for weed control, although many people use it together with a layer of gravel or pine straw on top to give it a natural look.
Landscape fabric, also called weed fabric, is usually made of woven plastic, linen, or recycled fibers. It can also be made from a single solid sheet with tiny perforated holes. The fabric comes in rolls, usually 3 feet (90cm) wide and 50 – 200 feet (15 – 61 m) long.
Pros: It does not decompose easily and so can last for many years, at least 10 or even 30 years. In the beginning, it may give you a false impression that no weeds are coming up.
Cons: However, after a few months you will start noticing weeds cropping up.
Weed seeds will land on top and they will germinate on top, especially if there is another layer of mulch above acting as a substrate to trap moisture to encourage germination. The roots can find their way through the tiny holes of the landscape fabric. When you try to remove and tear out the weeds, you can easily rip the fabric.
Another downside with using landscape fabric is that you cannot garden with them, especially if you change your mind one day and want to put a plant in the area with fabric.
Also, the fabric does not let your garden breathe, depriving the soil underneath of oxygen which not only affects the health of your garden (making the soil underneath anaerobic, which can even stink). It will also affect the roots of the trees, shrubs, or the plants you have nearby.
Also, there can be a lot of runoff when it rains, and is thus not suitable for places with much rainfall.
Similar to landscape fabric, plastic mulch is not a good option for home gardens and yards to suppress weeds.
Pros: Plastic mulch is used widely in agriculture mostly because it is cost-effective to use over a large piece of land. It can somewhat inhibit weed growth only because no other mulch is put on top to act as a substrate for weed seeds that land on top to germinate. Also, plastic sheets do not decompose and can last for a couple of years.
Black plastic is more effective than clear plastic as sunlight can pass through and can trigger weeds to germinate. Also, clear plastic is often thinner than black plastic.
Cons: For home gardens and yards, it is unappealing to cover the ground with only a piece of plastic and it does not allow the soil and the plant roots below to breathe. If you topdress it with a layer of natural mulch to give it a more natural look, weeds will grow on top because it traps moisture for seeds to germinate, just like the landscape fabric.
Also, plastic does not allow the soil and plant roots underneath to breathe and when it rains, there will be a lot of runoff as the water cannot penetrate through the plastic.
3. Artificial grass
Artificial grass can suppress weeds but it does not look appealing and you cannot garden with it.
Pros: It is made of synthetic fibers designed to look and feel like real grass. It consists of several layers including infill, backing, drainage, and cushioning layers. In most cases, there’s also a weed barrier added between the artificial grass and the soil. All of these layers make it almost impossible for grass to grow through.
Although it’s not unheard of for weeds to grow from the edges, these are surface weeds that can easily be removed by hand.
Another advantage of artificial grass is that it can last up to 15 years and will be effective against weeds throughout its lifespan.
Cons: Fake grass may not look very pretty and natural to many people. You cannot garden in it if you change your mind in the future. It also deprives the soil below of oxygen.
Gravel is a good option in suppressing weed growth as long as the layer is thick enough and with a bit of maintenance.
Gravel is rock fragments with more or less rounded edges, usually with a diameter of 3/8 to 1.5 inches (1 to 4 cm).
Pros: To prevent weeds from growing through gravel, the layer has to be sufficiently thick, up to 6 inches (15 cm).
Gravel gives it a natural look and allows for the soil and plant roots underneath to breathe.
It also offers more flexibility in landscaping for the future. In case you want to make some changes to your garden space and put a plant or tree in, you can easily remove the gravel of the spot.
Crushed concrete and limestone are similar to gravel and are equally effective in suppressing weeds.
Cons: You may still see a few weeds cropping up through the gaps but those are easy to plug out and remove a couple of times a year. In fact, weeds will always crop up with any kind of mulch, even with plastic as mentioned above.
For an organic option, wood chips are effective in suppressing weeds as long as the layer is at least 6 inch (15 min) thick.
They are shredded pieces of tree bark and twigs, usually between 0.5 and 1.5 inch (2 and 4 cm) long.
Pros: The chips work like gravel and crushed rocks, they cover the soil, preventing sunlight from reaching any weeds in the soil, so they can’t germinate. It also creates a barrier to prevent new weed seeds from getting into the soil.
They are also organic and add nutrients to the soil underneath when they decompose which is particularly beneficial for garden beds with plants.
Cons: Wood chips need to be replenished after a year as they decompose. As with all mulch types, some basic maintenance work such as pulling out weeds a couple of times a year is needed.
Pine shavings are not very effective against weeds and grasses.
They are very light and can be easily blown off. Also, pine shavings decompose much faster than wood chips, usually between 2 to 5 months if there’s enough moisture, and would thus need to be replenished quite often.
Pine straws are needles from pine trees. It is not very effective at suppressing weeds because of the gaps in the hay, letting in sunlight and moisture that encourages weeds to grow.
It will only be effective in preventing weeds if the mulch is at least 4 inches (10 cm) thick.
Also, pine straw will decompose within 6 to 12 months, depending on the temperature, and wetness. Consequently, the mulch will need to be refreshed and replenished every year to maintain the initial level.
Putting soil on top is not an effective way to suppress weeds.
In most cases, weeds can grow through up to 3 inches of added soil, and anything above 4 inches will be too much for the grass and weeds.
However, they can still grow on the surface. Also, there may be weed seeds present in the soil or they can land on it and would then germinate.
Newspapers or card boxes are great at preventing grass and weed growth but would need replacement every growing season.
The newspaper mulch needs to be at least 10 pages thick to be effective and can keep weeds away for an entire season.
Wet the paper lightly (you can do this with a hose) to prevent it from getting blown off by the wind.
Also, the edges need to overlap, if not weeds can grow in between. You will need to replace them every few months as newspapers or card boxes can disintegrate quickly.
Sand does not inhibit grass and weed growth.
Sand is actually a good medium for most plants because it retains some moisture. So, that also allows weed seeds to germinate and grow. Weeds such as dandelion, yarrow, and nettle in particular can grow well in sand.
Hay is the grass that was cut while it was still green and then left to dry.
Hay holds moisture and decomposes to add nutrients. However, it doesn’t do a great job of preventing grass and weeds.
Hay has a soft and spongy feel, with many entrances for air and sunlight to get to the soil and trigger weed growth. But more importantly, hay carries grass seeds that will eventually germinate.
Best mulch to suppress grass
All the different mulches can suppress grasses and weeds to an extent, but the best ones are wood chips, newspaper, landscape fabric, black plastic, and artificial grass.
The most effective mulch is a combination of
Generally, organic mulches are less effective at preventing grasses and weeds, as they have gaps and they add nutrients to the soil when they eventually decompose. Wood chips and newspapers perform well at suppressing weeds, as long as the mulch has a sufficient thickness. They don’t decompose too quickly, and may only need to be replaced once a year.
Gravel, crushed concrete, and limestone are effective in suppressing weeds as long as they are 6 inches thick.
Landscape fabric and artificial grass are designed specifically to prevent weed growth, and it works as intended by preventing sunlight from getting to the weeds in the soil. It is durable and can successfully keep grasses and weeds away for up to three years.
Finally, black plastic covers the soil and prevents light from reaching the weeds. Black plastic is also effective at killing existing grasses, especially when used in the hot summer months. The plastic isn’t as durable as landscape fabric and typically lasts between 1.5 and 2 years.
Worst mulch to inhibit grass
Of all the mulch types discussed, the worst at suppressing grass are soil, topsoil, sand, and hay.
Soil and topsoil can indeed kill and suppress grasses, provided the depth is above 4 inches. However, the imported soil may contain weed seeds of its own which will emerge shortly. Even if it’s free of weeds, any weed and grass seeds that land on it will quickly germinate.
Sand is similar to soil. At great depths and thicknesses, it can prevent grass. But new grasses and weeds can grow on the surface.
Hay is dried grass, and usually has a few grass seeds present on it. When you use it as mulch, the seeds fall into the soil and germinate. And you end up with the very thing you were trying to prevent.
Which is your favorite?
Also check out the next article to learn how tilling can also be an effective way to control weeds.
University of Minnesota. (n.d.). Using the sun to kill weeds and prepare garden plots. UMN Extension.
Should I use landscape fabric to keep weeds out of my perennial garden? (2019, May 4). University of Hampshire Extension.
The disadvantages of landscape fabric. (2021, June 25). University of Illinois Extension.