Re: CULT: Preemergent

Kitty -- I have used Preen for 32 years. Whenever I establish a new bed, I apply the Preen as the last step, either mixing it into the top couple of inches of soil with a rake or, if I'm lucky, letting rain do it for me within 24 hours. I transplant both adult plants and new seedling sprouts from containers into the new bed as soon as I have applied the Preen and mixed or watered it in. But sometimes I have planted immediately after mixing in the Preen and watered afterwards. The Preen granules form a chemical layer that prevents germination of most weeds. Like most things, though, Preen isn't perfect. It doesn't work against some common grasses or morning glories. There is a preemergent called Snapshot that does work against morning glories and most grasses and can be applied right over your established plants, but it has become prohibitively expensive and is dangerous to use, because it will interfere with or prevent root growth of sprouts and even (I believe) retard newly-planted adult plants' adaptation to treated beds. It stays in the soil for a couple of years, so, if you use it on an established bed, where it will do an excellent job, don't think about using that bed for seedlings for about 3 years. -- Griff


----- Original Message ----- From: "Loberg" <loberg@adelphia.net>
To: <iris@hort.net>
Sent: Friday, July 14, 2006 2:03 PM
Subject: [iris] CULT: Preemergent


I spoke once before about the preemergent Trifluralin (Preen, MiracleGro, others). I would be interested in hearing people's comments on the best timing to apply this product. I've used it in the spring, and fall, but not particularly when I'm digging and replanting irises. The idea is that it's not suppose to hurt irises that already have root growth established. The label by the product manufacturer doesn't list using it with irises, other than bulbous iris. What has been other's experience as to the timing of application of Trifluralin for preemergent weed control? Is it advisable to put on when planting, so that immediate watering won't bring up a fresh crop of weeds? Thanks.
Kitty Loberg
Northern Calif.
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