What's Happened To Peat Over The Past Few Years?
Wilbur L. Bluhm, Marion County Extension Agent Oregon State University
Reprinted from Ornamentals Northwest. Dr. James Green, editor
Virtually every grower has observed changes. Weeds such as oxalis, sorrel, and chickweed are now common in peat, but were formerly no problem. Some growers have noted reduced plant performance in peat in recent years.
Peat is often different than it used to be. Much of this difference, with many peat sources, can be traced to a change in harvesting methods. The newer slurry method of harvesting peat from a bog uses water which may be contaminated with weeds, diseases, and possibly other organisms.
Plant pathologists in Pennsylvania found diseases present in everyone of 52 peat samples they tested a couple years ago. Of these samples, 36 came from foreign countries. Some of them were labeled "sterilized", "No fungi", or "weed free".
Pythium, common water-mold fungi which cause plant diseases, was found in 15 of the 52 samples. Test plants of alyssum, geranium, grass (Poa spp.) and beans were all killed when treated with Pythium fungi isolated from the peat.
Fusarium, common plant disease fungi, was present in all 52 samples. Fungus gnat larvae have also been found in other peat samples on occasion.
This may help to explain why, in some cases, plants don't perform as well in peat as we expect. The peat we've considered to be sterile really isn't sterile - free of weeds, diseases, and other problems.
Peat or peat mixtures used for plant propagation, either cuttings or seed, should be heat or chemically treated before use.