While weeds are a nuisance no matter where they grow, decks can make them particularly irritating. Not only do the weeds get enough sun and rain to flourish because of the spaces between the deck slats, but they are also difficult to eradicate because of the limited amount of space beneath the deck. (Small weeds are especially tricky).
That being said, there are effective, long-lasting solutions to kill existing weeds and prevent new weeds from growing under your deck, including ground covers and herbicides.
Eradication Method #1: Manual Control
Depending on how high your deck sits from the ground, you may have an easy solution to your weed problem.
If your deck is high enough to walk or crawl beneath, you can just pull out the weeds as they grow. If your deck is too close to the ground to squeeze beneath, but still has some amount of space, use a long-handled hoe to rip up and kill the weeds.
Note: while this works well for annual weeds, perennial weeds have deep roots and will continue to grow back even after you pull them up. So, given the lack of space, manual eradication isn’t always the best method.
Eradication Method #2: Post-emergent Herbicides
Although the space between your deck slats is the cause of your weed problem, it might also be one of the solutions. Just like rain, herbicides can leak through the gaps and onto the weeds below, which is helpful if you are either unable to get under the deck or apply the herbicide from the sides.
Spray the weeds through the boards with a long-lasting, post-emergent herbicide. For any weeds that are poking out and above your deck, coat them completely. Reapply the herbicide whenever new weeds appear.
However, chemicals can be dangerous, and, for that reason, some people prefer to avoid them. If you are one of those people, a safe alternative to post-emergent herbicides is vinegar. The caveat is that it only works for newer weeds.
Older, well-established patches of weeds, on the other hand, can only be killed with something strong.
If you prefer to use chemicals because your weed problem is an old one and you know that vinegar won’t work for you, or you just want to be certain your problem is fixed, be careful with the application.
Wear clothing that minimizes exposed skin, like gloves, close-toed footwear, long sleeves, and goggles. Do not get close to the area, or let anyone else get close to the area, until the spray has dried.
If you feel a bit silly or overly paranoid, just remember that it’s always better to be safe than sorry.
How to Keep Weeds From Growing Under Your Deck
Prevention Method #1: Pre-emergent Herbicides
If you don’t have a gnarly patch of weeds growing under your deck yet but are looking to save yourself the trouble of dealing with one, pre-emergent herbicides kill weeds before and during germination.
Pre-emergent herbicides may save you the trouble of manually pulling your weeds out and treating them with post-emergent herbicides in the spring (and likely pre-emergent herbicides after that).
Again, if the idea of using chemicals is not appealing to you, there are alternatives. The most popular is corn gluten meal but, like any other pre-emergent herbicides, it is useless at killing weeds once they’ve started growing.
For an inexpensive method that claims to both prevent and kill weeds, add one cup of salt to two cups of boiling water and pour it over the ground beneath your deck. The salt soaks into the ground and increases the salinity of the soil, making it inhospitable to plant growth.
Prevention Method #2: Smothering the Weeds
A quick way to smother weeds is to spread a two to three-inch layer of mulch over them. However, mulch is only a temporary fix as the mulch breaks down over time and becomes ineffective. It may also cause fungal growth and wood rot.
Another often suggested solution is to use black plastic. But though black plastic is indeed effective at smothering weeds, it can lead to water collection, which can lead to an insect infestation.
If you are looking for a permanent solution that won’t cause any problems down the road, lay down a piece of fabric cloth. To do this properly, first, secure the ends with landscape stakes and then top the landscape fabric with three to four inches of gravel. This not only prevents new weeds from growing under your deck but also kills any existing weeds.
Laying down landscape fabric is by far the superior method of preventing and killing weeds, because it is quick, easy, and does not involve the use of chemicals.
It’s also very cheap! It will only set you back about fifty dollars for a four-foot by two-hundred-foot roll and, if you’re only smothering a small area, you might get away with spending as little as fifteen dollars. Landscape stakes, meanwhile, are about five to twenty-five dollars.
Don’t forget to factor in the fact that you’ll be saving on the costs of weed killer.
Prevention Method #3: Limit Water Flow
Another easy way to control weed growth is to limit the flow of water under your deck. When watering the area near your deck, use drip irrigation instead of sprinklers, which cover a much larger area. The drier the space beneath your deck, the less welcoming it will be to unwelcome plants.
Overall, the ultimate method for both preventing and killing weeds is to smother them with a layer of landscape fabric and top it with three to four inches of gravel. It is cheap, shouldn’t take much effort, and avoids the necessity of chemicals.
If you do use chemicals, remember to be safe and to choose between pre-emergent or post-emergent herbicides, depending on whether you are preventing a weed problem or getting rid of an existing one. You should also limit the amount of water flow to your deck, as the wetter the soil is, the more welcoming it is to weed growth.