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Consumers Beware Potting Mix Choices

By Carl Wilson, Extension Horticulturist

There's nothing more frustrating then potting a container plant only to experience poor plant growth. In many cases your lack of a "green thumb" may not be at fault.

A lot of your chance for success is determined by choice of a potting media that allows you to water effectively.

This is where research-based Cooperative Extension information will help. As the only Colorado university with horticulture, entomology and plant pathology departments, Colorado State University is your source for accurate plant growing information.

A two-year research project examined the major potting media sold by garden centers, nurseries and mass merchandizers. 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 many other flowering and foliage plants in containers.

First, chose a true potting media and not something labeled compost. Composts are best used as organic 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 isn't 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 definite benefits to growing annual plants in media that may be more costly but result in better plant growth. Chose a media 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
  • Southland Potting & Plant Mix
  • Black Gold All Purpose Mix
  • Permagreen General Purpose Potting Soil
  • Schultz's Instant Potting Soil Plus
  • Sunshine All Purpose

Research conducted by Professor James E. Klett, Department of Horticulture and Landscape Architecture, Colorado State University.
Research funding provided by the Garden Centers of Colorado.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010