'....can lose about 20 percent effectiveness." The coated pellets, may do better. I wonder if mixing with soil is better than just watering it in. Urea has to be "digested" by bacteria and changed to a "nitrate" before plants can use the nitrogen. I bet that would happen faster under the soil. If I were rich, I like osmocote best and we use Haifa Multicote an osmocote knock off, in container plants and some of those containers are dahlias. They do well with it. In fact I used to belittle dahlias grown in pots but using 20 gallon pots and three dahlias is a good combination. They look pretty and are easy to care for. Tubers are good too.
