Should I Put a Weed Barrier Under Mulch?

Using mulch in your Florida backyard has many benefits. It's recommended by local landscape designers as well as by UF's Florida-Friendly Landscaping program. But a question often asked by homeowners is whether to use landscape fabric or another weed barrier beneath this layer of mulch. Here's what our local experts have to say.

Why You Shouldn't Use Landscape Fabric Under Mulch

Homeowners choosing to use landscape fabric usually do so because they want to prevent the growth of weeds. This makes sense: the layer of fabric should block sunlight as well as physically preventing weeds from sprouting up out of the soil.

However, landscaping experts say that using a fabric barrier underneath mulch can actually have the opposite effect. This is because mulch is usually organic matter, such as wood chips. As wood mulch breaks down, it slowly becomes compost. If there is no layer of weed barrier, this new compost improves the soil by mixing with it.

However, where there is weed control fabric under mulch, you end up with a layer of compost on top of the fabric. As weed seeds are brought in on the wind or by animals, this new layer of soil on top of the landscape fabric becomes a haven for weeds.

Other Disadvantages of Landscape Fabric

Here are some other reasons why it may not be a great choice to use a fabric barrier beneath wooden mulch:

• Weed fabric can be bad for the soil, as it does not always allow enough moisture and air to get through. It can also prevent earthworms and other beneficial microorganisms from reaching the surface and allowing the soil to aerate.
• The lack of air, moisture and healthy soil underneath the weed fabric barrier can make it difficult for your chosen plants to thrive.
• Landscape fabric under mulch can prevent the mulch from decomposing properly. Instead of becoming compost and mixing with the soil beneath, mulch can become compacted into an unsightly solid block that is difficult to deal with.
• A fabric barrier makes it more difficult to replant. If you decide to move things around, you'll need to cut new holes in the fabric, which can be tricky when it's already in place.

Alternatives to Landscape Fabric

We've learned that landscape fabric is not recommended under mulch as a weed control method. So, what can homeowners do instead to reduce weed growth in garden beds?

The answer could simply be organic mulch itself. When applied properly, a layer of mulch will contribute to weed suppression. To ensure weed protection, spread a layer of wood mulch or bark mulch evenly around the base of plants. Make sure your mulch layer covers all areas of exposed soil.

On a perennial bed, aim for a one- to two-inch layer of mulch. For trees and large shrubs, aim for around three inches of mulch. Be aware that mulch will settle, so you may need to apply a thicker layer initially.

Benefits of Mulch

As well as reducing weed growth, the application of mulch has other benefits for your North Central Florida yard:

• Mulch helps to retain moisture, allowing you to avoid dry soil and grow a healthy garden with lower irrigation costs.
• Mulch can add curb appeal as part of your landscape design.
• A natural insulator, mulch helps to keep your soil temperature at a constant level.
• A layer of mulch helps with erosion control. It absorbs raindrops, protecting the layer of soil underneath and preventing it from being washed away by run-off water.

If you would like to add an additional weed barrier that will still promote healthier soil and the growth of healthy plants, choose a material that will decompose at a similar rate to the mulch. Newspaper or cardboard will make an effective weed barrier while promoting moisture retention in your landscape bed.

Another option for protection from weeds is to use a natural weed preventer such as Preen. This product will prevent new growth of plants for several weeks after application. To apply, begin by removing preexisting weeds. Wait for a time when the soil is dry and rain is not forecast for 48 hours, then work the product into the soil around your established plants.

When Is Landscape Fabric Recommended?

Using weed fabric under organic mulch is not recommended because it can create more problems than it solves. So, when do landscaping experts recommend using a fabric barrier to discourage weed growth?

The answer is that a fabric barrier can be helpful for weed suppression under materials that will not decompose, including river rock, gravel, and rubber mulch. This protective layer helps prevent weed growth because the inorganic materials on top of it will not decompose, so no new layer of soil will occur.

In addition, the appearance of inorganic mulches is improved by placing a layer of landscape fabric underneath. The fabric prevents mulch or gravel from mixing with the soil. This keeps it looking clean and bright, adding curb appeal to your landscape design.

Another advantage of weed barriers under inorganic materials is that they can prevent gravel or mulch from sinking into the soil. As well as looking tidier, it will need to be replenished less frequently.

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