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What to Put Under Deck to Prevent Weeds [7 Simple Tips]

Decks are amazing outdoor spaces, great for allowing friends and family to gather. However, whether you’re building a new deck or maintaining an existing one, you never want to see weeds cropping up between the boards. They can invite insects and unwanted animals, as well as detract from the appearance of your outdoor space.

To prevent weeds from growing beneath your deck, you should apply a ground covering of landscape fabric, followed by 3–4 inches of gravel. To kill existing weeds and prevent their return without investing in a ground covering, use long-term weed killers, natural weed killers, and pre-emergent weed preventers.

What to put under deck to prevent weeds

How to Keep Weeds From Growing Under Your Deck: 7 Quick Tips

There are a number of methods for preventing weeds from growing under your deck. Let’s review the best options, as well as methods to avoid.

Lay Down Landscape Fabric

Landscape fabric provides a water-permeable barrier over the soil that prevents weeds from sprouting. By laying landscape fabric, you prevent seeds and sunlight from reaching the topsoil, so even the toughest weeds have a hard time growing.

Add Gravel Over Landscape Fabric

Gravel is an attractive and useful ground covering. While, on its own, gravel may not stop all weeds from sprouting, combining it with landscape fabric creates a complete barrier. Apply 3–4 inches of gravel over your landscape fabric to keep the area underneath your deck weed-free.

Not only does the gravel cover unsightly landscape fabric, but it also protects it from the elements and any animal traffic, enhancing the lifespan of the landscape fabric you lay down. Gravel is the best choice for weighing down and protecting landscape fabric under your deck.

Avoid Plastic Sheeting

Landscape fabric is preferable to plastic sheeting because it allows water to pass through to the ground below. Plastic sheeting, on the other hand, can collect water in pools. This creates a breeding ground for mosquitoes and other bugs, as well as causing unpleasant smells. You don’t want your deck to be a bug haven or an area that smells like stagnant water.

Don’t Use Bark Mulch

While mulch can be a great choice of ground covering in a garden setting, it should not be used to suppress weeds underneath your deck. Even when it’s applied over landscape fabric, mulch in an under-deck setting can be troublesome.

Mulch is, after all, wood. In a low-light environment underneath a deck, mulch can remain damp, which invites fungal growth and wood rot, which can spread to your deck and house. If you are looking for gravel alternatives under your deck, consider synthetic mulches (such as mulch made from recycled tires) rather than organic materials.

Use a Long-Term Weed Killer

It’s probably a safe bet you don’t want any plants growing underneath your deck. Therefore, it’s the perfect place to go all-out with strong weed killers.

If you don’t want to invest the time and money into landscape fabric and gravel ground covering, you can combat weeds growing under your deck with a long-lasting weed killer such as RoundUp 365 or with a brush killer such as Crossbow. Long-lasting weed killers will stomp out existing weeds and keep the area beneath your deck weed-free for up to a year.

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09/16/2021 12:07 am GMT

Use a Pre-Emergent Weed Killer

Worried that the weeds beneath your deck are going to resprout in spring and you’ll have to fight them all over again? Invest in a pre-emergent weed killer and apply it in spring (late-March through early-April) to prevent weeds from growing under your deck.

Pre-emergent weed killers destroy weeds just as the seeds germinate. They won’t kill mature weeds, so apply pre-emergents early to make sure no weeds take root under your deck.

Try Natural Weed Killers

If you’d rather not use chemical herbicides to control the weeds under your deck, there are natural options.

You can use a weed killer made from horticultural vinegar (it’s much stronger than table vinegar and is available at most home and hardware stores) combined with a small amount of dish soap. Once mixed together, the soap will help the vinegar stick to the weed leaves, destroying the plant. Spray this on the weeds under your deck to get rid of them.

You can also use Corn Gluten Meal (CGM) as a natural pre-emergent weed killer. Apply it to the ground underneath your deck in early spring. It will absorb moisture and dry out weed seeds, preventing them from sprouting.

Keep Under Your Deck Weed-Free

Keep under deck weed free

A ground covering of landscape fabric topped with 3–4 inches of gravel is the best way to keep weeds from growing underneath your deck. The barrier will prevent weeds from sprouting and keep sunlight from reaching the soil.

To kill existing weeds under your deck, use strong, long-lasting weed killer for best results and apply pre-emergent weed killer to prevent new weeds from sprouting. Natural weed killers made from vinegar and natural pre-emergent weed killers such as Corn Gluten Meal allow you to achieve similar results without chemicals.

Remember, choose measures for weed control that will not create other problems. Using plastic sheeting underneath your deck can allow for water collection, which invites insects. Similarly, using mulch beneath a deck allows for fungal growth and wood rot, so these methods are best avoided.

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