To non-gardeners, bags of leaves left at the roadside are just so much waste material to be collected and disposed of by the city. But to the horticulturally cognoscenti, those leaves are plant duvets that keep the garden cozy all winter long. Like a deep blanket of snow, a four- to six-inch mulch of leaves protects perennials and shrubs from desiccating winter winds, and keeps the ground frozen so that plants stay dormant – their best protection against the weather. During a typical Toronto winter, we experience extreme temperature fluctuations, from warm sunny days that can trick plants into breaking buds prematurely, to deep freezes that can nip off those buds in no time. A deep leaf mulch moderates soil temperatures too, protecting plants from the damage that extreme temperatures can cause. But be picky about the leaves you “rescue” from the curbside: smaller leaves are best, such as birch, mountain ash, linden or locust. Most maple leaves (silver maples are okay) are too large and flat to make a good mulch – they tend to matt together, making it difficult for rainwater to percolate through to the ground. Apply the mulch once the ground has frozen to discourage mice and other rodents from nesting next to the roots of your prize perennials.