I've trialed several Euphorbia here, some as ornamentals and some for their purported ability to deter rodents. The one with the oldest and most widespread reputation is the mole plant, aka gopher spurge aka gophers purge, Euphorbia lathyris. My experiences suggest that it is useless for repelling rodents. I'll admit that I've never seen a mole tunnel or a vole run which goes under one of these plants, but if the Euphorbia is there, a bulb isn't. I happen to like this plant, and there are usually a few here and there in the garden. But I don't expect them to repel rodents. From what I've read, Tagetes are supposed to be good for getting rid of nematodes. Until I read Adam's post, I had never heard that they were good for repelling rodents. John Bryan asked why some bulbs are devoured and not others. One reason is that some contain bitter compounds of magnesium (or is it manganese? I always get those mixed up.) which make them unpalatable to all but starving critters. Certain lilies such as Lilium henryi and its hybrids, L. hansonii and its hybrids, are good examples. Jim McKenney Montgomery County, Maryland, USA, USDA zone 7, mid-forties today with warm sun after several days of unseasonably cold weather. Protected crocus are still blooming outside.