|Regarding voles and caging bulbs: I would have to have big cages to avoid having the tubers growing through the mesh...and this hardware cloth is quite expensive. I heard that voles do not dig below 6 inches and that if I put a barrier 6 inches deep around the whole patch, I could avoid the extra work. I could dig a trench around the garden and lay in some 6-inch (or greater) wooden boards. I have a good supply of barn boards available to me for nothing. They are an inch thick. I realize they will eventually rot-out, but I dig the garden up almost every year or so anyway, and there is an abundance of boards. The final question is whether voles would gnaw through an inch board?
|A fence 18 inches high and 6 inches deep will deter most small rodents. Regarding a barrier flush with the soil surface and buried to 6 inches: I would think that if the voles are determined enough, they will walk over the wooden barrier you propose and start digging once inside. However, this type of deterrant may make enough of a difference that your problem is diminished sufficiently, especially if there are other plants attractive to the creatures nearby.
Other things to try, either alone or in addition to your buried fence:
Interplanting bulbs that the animals won't eat--notably daffodils and various allium species.
Surrounding the bulbs with coarse gravel in the planting hole.