When it's time to replace container plants, repot houseplants, or start seeds, most gardeners purchase a bag of potting mix. It is such a common component of gardening that we never give it much thought - until we stand in front of a half-dozen brands and formulations and try to figure out which bag to bring home.
Instinct tells us to steer away from the least expensive, especially if it seems to be half the volume and twice the weight of the others, but is there really a difference in potting mixes?
I asked Hugh Poole, the director of Technical Services/Quality Control of Fafard, and he invited me to visit the Fafard facility and laboratory in South Carolina to learn more about the science behind potting mix. Fafard mainly creates mixes for growers whose livelihoods depend on consistency and quality for growing healthy plants uniformly and quickly.
"We want all of our clients to succeed." Dr. Poole explained. "We don't make a distinction between homeowners and growers."
The 20 percent of Fafard's mixes and components sold directly for the home gardener benefits from the stringent standards and testing that professional growers require. During manufacturing, tests for pH, soluble salts, percolation, water retention, bulk density, and volume are done on mixes.
Tests also are done on many individual components, such as the wetting agent and bark, and samples are stored for two years. A sample from each batch is sent to Fafard's lab for full analysis.
There also is a greenhouse on site to grow indicator plants (often impatiens) in sample mixes. Beside the greenhouse is Fafard's three Plant a Row for the Hungry raised beds, where vegetables are grown for charity (1,000 pounds last year).
The wetting agent and the fertilizers are the two main components that must be changed for a mix to be certified as organic. Professional organic growers have grown in numbers and production.
To meet their needs and standards, organic alternatives to chemical wetting agents were developed. These mixes are available to those who would rather garden with organic potting mixes.
"Be more careful about plants in organic mixes," Dr. Poole said. "With organic wetting agents, the mix should contain more water and not be allowed to dry out."