The following is a quote taken from an e-mail that I got from Paul Black when I asked him what they do to prevent weeds.
"We alternate two products, Ronstar and Snapshot. We use them after we work the beds and have the irises replanted. We dig and replant almost everything, every year. Don't incorporate it into the soil before planting. It will inhibit root growth. Treflan is one of the most potent. I don't use it. It tends to inhibit root growth whereas the others don't when used properly. Most of them come granular and liquid. Be sure to read and follow label directions."
I'm not sure if the active ingredient in Preen is the same as these two or not. I haven't been able to locate a sourse for either product mentioned locally, so I haven't tried it.
