Best soil for raised bed gardening? Results are in

2011-09-10T00:25:00Z 2011-09-12T14:18:16Z Best soil for raised bed gardening? Results are inCaleb Warnock - Daily Herald Daily Herald
September 10, 2011 12:25 am  • 

"You can graze like a cow in your own yard."

This is how Megan Ranstrom describes her work overseeing vegetable soil trials for the Central Utah Water Conservancy District in Orem. This summer, Ranstrom and her horticultural assistant Casey Finlinson tested four soil types for raised bed gardening, and now the tantalizing results are in.

Different soils produced yields night and day apart.

Of the four plots, the two using commercial loam topsoil did the worst. The two plots using commercial artificial soil simply exploded with vegetables, including the largest tomato plant a Daily Herald reporter had ever seen, perfect yellow Spanish onions, and great beans, melons, peppers, cucumbers, chard, strawberries and more.

The good news is that all four plots produced great vegetables. But the two with artificial soil far and away yielded more -- much, much more.

The soils tested were first, loam topsoil purchased at a local greenhouse, with nitrogen added at 21-0-0; second, the same soil and nitrogen with "Black Gold Compost Blend"; third, "Mel's Mix Square Foot Gardening Soil"; and fourth, "Miller's Mix."

Surprisingly, the loam-compost mix yielded the least vegetables, Ranstrom said. The same mix with just nitrogen yielded slightly better. The "Square Foot" mix probably tripled the yield of the first two, and Miller's Mix did even better.

But there is a catch.

Ranstrom, Finlinson and consulting experts from the county extension service warn that artificial soil is designed to perform exactly as it has in these trials -- but next year, it will be more or less completely depleted and will either need to be replaced entirely or replenished with lots of commercial fertilizer. The loam soils, however, will be far less expensive over the long term.

So Ranstrom leaves it up to individual gardeners to interpret the results of the trials, and invites gardeners to come and see the raised beds and their produce for themselves.

Meanwhile, the conservation district is going to continue the tests, especially because so many questions have risen based on the results.

For starters, the top soil tested at pH 7.9, Miller's Mix at 5.67 and the Square Foot Mix at 7.84. What if you could use elemental sulphur or organic material to lower the pH of the loam -- would it then perform as well as the more expensive artificial soils? What about a completely organic soil mix, which thus far has not been tested? Why did adding compost seem to reduce the yield of the loam?

Whatever future trials may show, one thing is sure.

"Soil makes it or breaks it," said Ranstrom of gardening.

Gardeners curious about the soil trial results can see for themselves. The conservation garden is open to the public Monday through Friday, from 8 a.m. to 8 p.m. through Sept. 15 and 8 a.m. to 4:30 p.m. beginning Sept. 16. The Central Utah Water Conservancy District garden is at 355 W. University Parkway in Orem.

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