The Garden Gal, October 7, 2012 — Debbie Cook, the Garden Gal, a master gardener and certified arborist tells us that your leaves, except for walnut tree leaves, are the best thing you can do for pure mulch. She also recomends that every three to five years, you have your garden soil tested before you start amending and planting in the spring. There are several labs that will give you a list of nutrients and elements that are needed or are too high for optimal growth. But give them a call first to find out where they want you take your soil sample from.