TL;DR
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A two-year trial at Sweet Hollow Farm in Idaho found cardboard-mulched beds had 15% weed coverage, compared with 45% in traditionally tilled beds, and some crops yielded up to 97% more. Gardening Know How’s writer also reported a strong personal harvest, but that single-bed test is not scientific evidence that cardboard caused the result.
A two-year trial funded by the U.S. Department of Agriculture found that vegetable beds mulched with cardboard had less weed coverage than traditionally tilled beds, while some crops produced yields up to 97% higher. Gardening Know How also reports that its writer’s own cardboard-mulched bed produced a strong harvest, though that personal test does not establish that cardboard alone caused the result.
The trial was a collaboration between the University of Wyoming and the USDA’s Western Sustainable Agriculture Research and Education program. Researchers grew a variety of crops over different seasons at Sweet Hollow Farm in Victor, Idaho, where the growing season is short. The report says some crops increased by as much as 97%; it does not identify those crops or provide detailed yield figures for each one.
Weed coverage in the cardboard-mulched beds was reported at 15%, compared with 45% in beds managed with traditional tilling. The trial used two layers of corrugated cardboard and placed four to six inches of compost over them before planting. Seedlings were planted through holes in the layers.
The Gardening Know How writer says they used one layer of cardboard on a vegetable bed during the summer and assessed it in October. They reported that the bed was 95% free of weeds and yielded their best harvest to date. That comparison was informal, based on the writer’s own garden, and was not presented as a controlled experiment.
Less Weeding, Potentially Larger Harvests
The trial results suggest cardboard mulch may serve two practical purposes for vegetable growers: reducing weed coverage and, for some crops under the conditions tested, supporting higher yields. Fewer weeds can mean less competition for water and nutrients, while a mulch layer may help soil retain moisture. Those are plausible benefits, but the report does not isolate which factors drove the yield increases.
For gardeners, the method may also make use of clean, unwanted cardboard rather than sending it directly to recycling. The reported results are encouraging, but they should not be treated as a guarantee of a bumper harvest: outcomes can vary with crop, soil, weather, cardboard preparation and the amount of compost used.
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How the Idaho Trial Was Set Up
The research took place at Sweet Hollow Farm in Victor, Idaho, a location described in the report as USDA Plant Hardiness Zone 4 with a very short growing season. The two-year project involved a variety of crops and more than one growing season, rather than a single crop in one plot. Its comparison included cardboard-mulched beds and beds managed with traditional tilling.
The trial’s approach was more than simply laying cardboard on bare soil. It used two layers of corrugated cardboard, covered by four to six inches of compost; seedlings were transplanted through planting holes. The gardening report recommends brown, uncoated cardboard and says labels and tape should be removed. It advises overlapping sheets by at least six inches where persistent weeds such as bindweed are a concern. These preparation details are recommendations in the report, not separate findings established by the yield comparison.
“My veg bed is not only 95% free of weeds but I’ve enjoyed my best-ever harvest.”
— Gardening Know How report author
Limits of the Reported Results
The report does not name the crops that reached up to 97% higher yields, provide crop-by-crop measurements, or explain how yield differences were calculated. It also does not give full information on the trial’s plot sizes, replication, statistical analysis or conditions across the two years, so readers cannot assess those details from the report alone.
The writer’s 95% weed-free estimate and best-ever-harvest assessment are personal observations, with no measured yield comparison or control described for that test. The report also does not establish whether the same effects would occur in other climates, soils or growing systems. The available information supports the specific reported findings, not a universal claim that cardboard mulch will increase every gardener’s harvest.
What Gardeners Can Monitor
No further trial results or follow-up research are announced in the report. Gardeners trying the method can track crop yields and weed coverage against an untreated or conventionally managed bed, while keeping growing conditions as similar as possible. That would help distinguish a perceived improvement from a measured difference.
The report advises using uncoated brown corrugated cardboard, removing tape and shipping labels, and covering the cardboard with compost as in the trial. It also recommends overlapping sheets to block persistent weeds. Those instructions reflect the gardening report; the trial’s reported results remain limited to its Idaho site and tested conditions.
Key Questions
What did the cardboard-mulch trial find?
The report says weed coverage was 15% in cardboard-mulched beds, compared with 45% in traditionally tilled beds. It also says some crops produced yields up to 97% higher, but does not identify those crops or provide detailed measurements.
Was the writer’s bumper harvest part of the trial?
No. The writer describes a separate, informal test in their own vegetable bed. They reported a strong harvest and about 95% weed-free coverage, but did not describe a controlled comparison or measured yield data.
How did researchers apply the cardboard?
The reported trial used two layers of corrugated cardboard, covered with four to six inches of compost. Seedlings were transplanted through holes in the layers.
Does the report show cardboard mulch works for every garden?
No. The reported findings come from a particular two-year trial in Victor, Idaho, and the article does not establish that the same yield effects will occur across all crops, soils or climates.
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