We often say that many houseplants should be treated with benign neglect, that is, place them in a well-lit room, then water infrequently and fertilize sparingly. That is especially true of succulents and cacti, the Thimble Cactus a case in point. This cute but spiny cactus does best in full sun, so it can hang out in the garden all summer, but the minute temps start to drop below 45 degrees, bring it indoors until warm weather returns. The Thimble Cactus goes dormant in the winter, so pretend your house is a desert and refrain from watering it, if at all. During the growing season, water it deeply but only when the top soil is dry, dry, dry. It will grow fairly quickly into a mound of thimble-shaped segments, sending out pale yellow blooms from late summer into the fall. As the botanical name 'fragilis' implies, those segments break off easily, but they often root, spreading even more rapidly into a tight mound.