Customers and clients often ask us about garden clean-up: When is the best time - spring or fall? Well, it turns out the answer is YES and NO! For most herbaceous perennials and ornamental grasses we feel it is best to leave the cleanup until spring, but there are exceptions. For many plants, leaving the mess until spring has several advantages. One, the dried seedheads and foliage of herbaceous perennials provide food and shelter for birds, overwintering beneficial insects and butterfly cocoons. Two, the frosted tops of plants can act as blankets through the winter, protecting plant roots and crowns from winter dessication and freezing. This is especially true with plants that are marginal in your growing zone anyway. Three, some winter foliage and seed heads, like those of ornamental grasses and coneflowers, remain attractive and add structure to your winter garden right on through to spring. HOWEVER, perennials that are always plagued by disease and pests, like bee balm (Monarda didyma) and garden phlox (Phlox paniculata) with their mildews, and German Iris (Iris germanica) with iris borers, should be cleaned up in fall and cut back to a couple inches above the soil to reduce overwintering of disease and pests. It is really just a common sense approach: Evaluate each species on its garden performance including the positives and negatives, and clean up in the fall only when it achieves a positive result.