Boyce wrote, >To increase the probability of providing soil temperatures cool enough to >perennialize some of the Mediterranean species of tulips try planting them >on the north side of a structure and/or in the cracks between large paving >stones. Photo's taken of Tulipa species in the wild in Central Asia >indicate a number of them grow in really rocky habitats. I thought this >was only to reduce predation by herbivores but there is a cooling component >as well. Both microclimates (north side of a structure and use of large >stones) are amazingly efficient at reducing the temperature of the soil. A method I used with success in my former garden was as follows. After planting bulbs on a raised bed with a gritty soil incorporating coarse, sharp sand with the native gritty clay loam, I spread a single close layer of basalt rocks around the size of medium to small apples (I had an infinite supply of these in the rocky soil there). Then I spread a layer of the coarse sand over the rocks and top-dressed it with pea gravel. Low-growing rock plants and subjects such as Acantholimon went in as my seedlings got enough size. Many plants that I thought might not be cold-hardy there grew well for many years. I haven't done this in the new garden because I didn't bring small rocks (I brought a lot of large ones for rock garden construction), but it's a good way to use up a size of rocks that aren't good for visible construction. Jane McGary Portland, Oregon, USA