Sam Franc > Some times very well growing dahlias do not regrow in the spring. > Does anyone know what could possibly be the reason? > Are there certain varieties that are weak this way? Hi, Sam If you are in Oregon, particularly western Oregon, as suggested by your ISP address, there are a couple answers. First, Dahlias are only borderline hardy here. Some of them will make it with little care, but many, particularly the newer, "fancier" hybrids, may not. Second, western Oregon is wet in winter, and dormant Dahlia tubers may rot. A raised position such as a raised bed, with excellent drainage, is a good idea. Covering with something to divert some of the rain will also help. If you use a sheet of plastic, slugs and snails love to crawl under, and anything under the plastic is lunch for them. Raising it up so there is air circulation under the plastic helps. You may still need to use a slug poison. If by "well growing" you mean the clumps have become crowded, they may have pushed themselves up almost out of the ground, and are more susceptible to frost damage. Digging every fall, or perhaps every other fall--half this fall, the other half the next--may be a good idea. Ken