Knowledgebase

Raised Bed - lining and stakes #751998

Asked May 25, 2021, 10:12 AM EDT

Hello, 1. I was wondering if there is such a thing as too much lining for a raised bed? I got landscape fabric to line the bottom and edges of of the wood barrier which is just sitting on top of the ground. I put down 4/5 layers of fabric. Is that too much and might it negatively impact drainage? I did this thinking it might be better to put multiple layers to lessen the likelihood of passage of plant diseases from the ground to the plants that will be planted in the bed, however, I'm guessing if water can pass through so can diseases anyways, and I got stuff from the ground on both sides of the fabric anyways so any effort at separation for disease purposes may be moot? I also put an extra layer to try to keep soil from seeping out the sides of the bed since the border is just sitting on top of the ground and the ground is not entirely even. I think this is the fabric I used: https://www.homedepot.com/p/Vigoro-40-in-x-36-ft-PLA-Natural-Weed-Block-Landscape-Fabric-NMV4036BPLA/310978002#product-overview 2. I cut some holes in the fabric and some hammered some metal stakes into the ground within the raised bed area to hold the fabric in place. The ground below is pretty tough and the stakes were long so in hammering metal flakes came off the stakes. I was wondering if I should have any concern about letting those flakes sit there, or using metal stakes in general. Is there any risk of somehow contaminating the bed soil? I'm not sure but the stakes might be made of galvanized steel?

District of Columbia County District of Columbia

Expert Response

Hi- the weed barrier material is unnecessary. It may interfere with air, roots, water, and soil critters moving between the raised bed soil and the soil below the raised bed, and it won't reduce the risk of disease problems. It's also unlikely that the weed barrier would extend the useful life of the wood. Ultimately, weed barriers left in place for years will slowly degrade into micro- and nano- plastics. 

If possible, remove the weed barrier under the raised bed. It sounds like you are also using the weed barrier as a mulch on top of the raised bed. That can work fine for that purpose. Tiny amounts of metal from the fence posts will not harm the soil, plants, or animals. There is no human health risk.

Weed barrier materials are also useful for smothering and killing weeds and mowed cover crops. Never cover them with organic mulches. Weeds will germinate on top and grow their roots through the fabric locking it in place and making weed and barrier removal very difficult.

Jon

Answered by the Home & Garden Information Center's Maryland Certified Professional Horticulturists Replied May 25, 2021, 10:44 AM EDT
Thank you so much for responding and for the helpful information.

I am putting setting up the bed for someone else and I passed on the information you provided, however They are somewhat insistent on a weed barrier (I haven’t yet filled it with soil). Is the micro plastics still a concern if the fabric is made of corn byproduct? 

To make sure I understand. You were saying that using a weed barrier during the non-growing season on top of the bed to rid of weeds is okay?

Thanks again,
Adam

On Tuesday, May 25, 2021, Ask Extension <<personal data hidden>> wrote:
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Dear adamlibe, here's the response to your question:

Hi- the weed barrier material is unnecessary. It may interfere with air, roots, water, and soil critters moving between the raised bed soil and the soil below the raised bed, and it won't reduce the risk of disease problems. It's also unlikely that the weed barrier would extend the useful life of the wood. Ultimately, weed barriers left in place for years will slowly degrade into micro- and nano- plastics. 

If possible, remove the weed barrier under the raised bed. It sounds like you are also using the weed barrier as a mulch on top of the raised bed. That can work fine for that purpose. Tiny amounts of metal from the fence posts will not harm the soil, plants, or animals. There is no human health risk.

Weed barrier materials are also useful for smothering and killing weeds and mowed cover crops. Never cover them with organic mulches. Weeds will germinate on top and grow their roots through the fabric locking it in place and making weed and barrier removal very difficult.

Jon


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The Question Asker Replied May 27, 2021, 9:30 AM EDT

Hi- bio-degradable mulches made from corn starches is a good alternative to petroleum-based barriers. The common complaint with these products from commercial growers is that the rate of demposition may be uneven and somewhat unpredictable.

Yes, weed barrier material on top of beds is good for smothering unwanted vegetation at any time.

Jon

Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 27, 2021, 10:25 AM EDT

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