Hi Benjamin,
Generally, bottoms on raised beds are not good for soil health, as the plants absorb the available nutrients the first season, and there's little to no soil life (the microbes, worms, fungal networks can't migrate up from the soil with closed bottoms) - requiring heavy amendments and/or soil replacement every other year. And as mentioned in other replies, drainage may be an issue depending on conditions in your area. Even fabric cloth under the beds creates challenges for veggies to thrive.
However, if the beds are being built on top of cement, there's nothing you can do other than replacing/heavily amending the soil.
Regarding the concern for weeds, it's only grass that poses a real challenge imho. And there's no real solution to that other than good cultivation in the fall and spring to remove runners. If you're building on top of grass and you can't remove it (if it's not sod), we've had success laying down cardboard, extending a foot or more past the beds (ie, the paths between and around the beds). Past the beds we mulch with 4 - 6" wood chips - we've tested covering the path cardboard with landscape-grade fabric and then adding the mulch. The cardboard under the beds is covered with half-compost, half soil. Not much grass pressure the first season, but the roots from under the cardboard creep around the interior edges of the bed, so we are diligent in weeding deeply to remove the runners. By the third season we no longer have much weed pressure from the grass, but if we don't attend to it, by the end of the season it's a big job to clear it out.
Ultimately, i think this is an issue for the organization - is there someone paid to be in charge of the garden maintenance/weeding. If not, I hear what facilities is saying and it's likely grass will take over the beds.
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sue salinger
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Original Message:
Sent: 04-28-2026 04:22:46 PM
From: Benjamin Driscoll
Subject: Raised Beds
Hello Everyone,
Seeking some advice on raised beds. We are (re)building our big growing area at school and trying to find a happy medium with facilities. They are very much in favor of our raised beds having a bottom to help with weed control in the future. I much prefer cedar beds for lots of reasons. Anyone have a good suggestion for raised beds that are not metal that have a bottom? I need at least nine 7X3 beds.
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Benjamin Driscoll
Sacramento CA
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