Compost: the new peat?

Composted wastes of plant, animal, and even human origin are now widely used in soil amendment and as components of substrates for plant growth.

C&C Peat Company has been producing potting soil for the nursery industry for 30 years. The Central Florida company originally used peat as the main substrate in its mixes, but has increased its reliance on organic compost as an alternative.

During the past eight years, C&C has reduced its volume of peat harvested by 60 percent. The Florida peat used in C&C’s mixes comes from its mining site in Groveland, Fla. Mining, especially in a wetland, as is necessary for peat harvesting, is a sensitive environmental issue. The process of acquiring mining permits and the wetland mitigation that comes along with it is time consuming and expensive. By replacing a significant portion of the peat harvested with compost, the company increases the longevity of its mining sites and has less of an impact on the environment.

“We have always produced custom mixes for nurseries, compost has simply become another tool in the chest,” says Stephen Cook, C&C Peat’s owner and president.

The company operates a 20-acre composting and mixing facility. Agricultural waste and other recyclable products, like horse bedding, land clearing debris, animal manures and food waste are brought to the facility and mixed together in a specific proprietary formulation. This creates compost that has very similar physical and chemical characteristics to native peat. Some mixes do not include any compost; some include up to 40 percent.

Right now, there isn’t much difference cost-wise between peat and compost, but that could change. While compost is slightly less expensive to produce in today’s market, its production cost is stable. As permitting becomes more restrictive, it could become significantly less expensive to produce than peat.

This is a worldwide issue. In fact, the International Horticultural Congress, which takes place Aug. 17-24 in Brisbane, Australia, is hosting a symposium titled “Organic Waste to Horticultural Resource.”

Pressure to reduce peat as a growing medium in some countries has led to the use of renewable resources such as bark, coir and green compost: all formerly regarded as wastes.
 

Compost concerns

Incorporating compost into the growing mix works well for some nurseries, but not others. There are a few factors to take into account.

The nitrogen, phosphorus and potassium in compost can have effect on a grower’s nutrition programs.

“If they are in a situation where they are rooting cuttings, and they want an absence of nutrition for the first six to eight weeks of the crop cycle, then compost is not a good choice,” Cook says. “However if they are plopping a 3-gallon tree into a 15-gallon container, then some compost in the mix is a benefit because of that nutrition.”

Growers should also consider their sources of fertilizer. Compost includes beneficial fungi that help to break down inorganic sources of nutrition to organic sources so the plants can utilize them. If a grower uses a lot of inorganic fertilizer, compost would be more beneficial. If a grower is already on a program using all-organic fertilizer, the nutrient availability of compost may not matter as much.

Another challenge is integration into a nursery’s IPM system. Growers often have pesticide management programs that drench for root rot-causing organisms and other pests. Before incorporating compost into the mix, growers should look at the pesticides they are using to see if they are killing off the beneficial fungi in the compost – negating some of the benefit of using compost as a substrate.

Cook says a lot of compost on the market is being produced from a “waste management” perspective – not necessarily a product targeted to the horticulture industry. Nurseries should be sure compost is free of VOCs (volatile organic compounds) that could possibly damage plant tissue. Look for independent verifications of quality, like the USDA Certified Biobased product label.

Matt McClellan is managing editor of Nursery Management magazine, a sister publication.