Potting Mix Trials By Holly Vesey I used to have a favorite seed starting mix and potting soil—Peters. Since they were bought out by Scott’s, however, I have been searching for a new favorite. I just don’t think I am getting the results I used to with the various mixes I’ve tried. Now comes research to back up my concern. Two recent articles in Hortideas (750 Black Lick Road, Gravel Switch, KY 40328) referenced a study conducted by Utah State University in which only 1 growing mix out of 24 tested was found to met standards for “premium” mix chemical properties as published by North Carolina State University. Large variations were found among the mixes in both physical and chemical properties known to affect plant growth. Unfortunately, these articles did not name names, so I decided to investigate a little further and found results of research conducted by Professor James E. Klett, Department of Horticulture and Landscape Architecture, Colorado State University. And it does name names. The two-year research project examined the major potting media sold by garden centers, nurseries and mass merchandisers. This replicated research indeed showed that potting mixes produce different plant growth results. Done with geraniums and impatiens, the following results are likely transferable to growing other flowering and foliage plants in containers. First, choose a true potting medium and not something labeled compost. Composts are best used as organic soil amendments for outdoor soils. The two composts trialed, Great Plains Compost and Mushroom Compost, produced poor results. Second, Hyponex All Purpose Potting Soil and Green Charm resulted in poor plant growth. Both of these media contain sedge peat, a fine particle material that tests to a low porosity. There simply is not enough space within these media for the water and air that plant roots need to grow successfully. Black Gold All Organic Potting Mix resulted in significantly less plant growth in one out of two years. There are definitely benefits to growing annual plants in media that may be more costly but result in better plant growth. Choose a medium from any of the following. The study showed no significant differences in plant growth among these products: Home & Garden Showplace Professional Mix Fertilome Potting Mix Nature’s Yield Potting Soil Black Gold All Purpose Mix Permagreen General Purpose Mix Schultz’s Instant Potting Soil Plus Sunshine All Purpose So, there you have it. I have used Nature’s Yield and Sunshine with good results, but I still long for Peters. Author’s note: This information was obtained from CSU Cooperative Extension web site (www.colostate.edu) written by Carl Wilson, Denver Extension Horticulturist.

Potting Mix Trials

Holly Vesey

I used to have a favorite seed starting mix and potting soil—Peters. Since they were bought out by Scott’s, however, I have been searching for a new favorite. I just don’t think I am getting the results I used to with the various mixes I’ve tried. Now comes research to back up my concern.

Two recent articles in Hortideas (750 Black Lick Road, Gravel Switch, KY 40328) referenced a study conducted by Utah State University in which only 1 growing mix out of 24 tested was found to met standards for “premium” mix chemical properties as published by North Carolina State University. Large variations were found among the mixes in both physical and chemical properties known to affect plant growth.

Unfortunately, these articles did not name names, so I decided to investigate a little further and found results of research conducted by Professor James E. Klett, Department of Horticulture and Landscape Architecture, Colorado State University. And it does name names.

The two-year research project examined the major potting media sold by garden centers, nurseries and mass merchandisers. This replicated research indeed showed that potting mixes produce different plant growth results. Done with geraniums and impatiens, the following results are likely transferable to growing other flowering and foliage plants in containers.

First, choose a true potting medium and not something labeled compost. Composts are best used as organic soil amendments for outdoor soils. The two composts trialed, Great Plains Compost and Mushroom Compost, produced poor results.

Second, Hyponex All Purpose Potting Soil and Green Charm resulted in poor plant growth. Both of these media contain sedge peat, a fine particle material that tests to a low porosity. There simply is not enough space within these media for the water and air that plant roots need to grow successfully. Black Gold All Organic Potting Mix resulted in significantly less plant growth in one out of two years.

There are definitely benefits to growing annual plants in media that may be more costly but result in better plant growth. Choose a medium from any of the following. The study showed no significant differences in plant growth among these products:

Home & Garden Showplace Professional Mix
Fertilome Potting Mix

Nature’s Yield Potting Soil

Black Gold All Purpose Mix

Permagreen General Purpose Mix

Schultz’s Instant Potting Soil Plus

Sunshine All Purpose

So, there you have it. I have used Nature’s Yield and Sunshine with good results, but I still long for Peters.

Author’s note: This information was obtained from CSU Cooperative Extension web site (www.colostate.edu) written by Carl Wilson, Denver Extension Horticulturist.