Hi, Carolyn: In addition to Roy and Boyce's remarks: >I've had some bad experiences with a pre-emergent getting down too >deep in the soil and inhibiting root growth >but I've also had success when >I have had sufficient organic matter to bind the pre-emergent very >close to the surface. At one time I had a small nursery, and weeds overwhelmed me-especially at first. When I considered using a pre-emergent (at that time Casoron for fall application and Simazine for spring), several things I remembered caused me to decide not to use pre-emergent herbicides. First, my nursery management professor several times complained that many nurseries didn't get good results from Casoron because they went elk hunting when they should have been applying the Casoron--meaning that timing of the application to catch germinating seedlings before they got too large and grew roots below the pre-emergent, was critical. Second, I visited one nursery in Washington where after several years he couldn't grow plants in the ground, in fact even weeds wouldn't grow--well, preventing weeds had been his intent, but even his crops wouldn't grow. He finally began to grow plants in containers, as even plowing the soil (turning over the top 8") wasn't enough. He finally sold the property and established a new nursery elsewhere. I know he used Casoron, he may have used Simazine, but I wasn't present when he used either. Third, a local nursery here in Oregon growing rhododendrons. They applied Casoron around established plants in the ground, and felt that the plants simply did not grow well afterward. Even by moving plants to another area of the nursery that hadn't been treated, the plants did not grow well for a year or two. These nursery owners were careful to apply the right amounts, the soil was highly organic and mulched with bark mulch, and they felt the Casoron prevented new roots from growing on these older rhododendrons. Note that both of these nurseries were applying Casoron to rhododendrons, which have a fine, fibrous, and shallow root system, as contrasted to something like the coarse, deep root system of roses. Newer herbicides, or different crops, probably would give different results, but I for one would be very careful to test in small areas before using. Ultimately, in my nursery, I did manage to control weeds fairly well without the use of pre-emergent herbicides. It did take time, and the weed population changed, depending on which weed control techniques had been used. So far, nothing seems to work for everything, but a combination works fairly well. Note that, when you manage to control one weed, a different weed often becomes dominant, so changing techniques and herbicides is necessary. Ken