Organic mulch can be made of shredded bark (the most common), leaves (except oak), wood chips, pine needles, or grass clippings. Mulch is an insulator and is best applied when the soil is warm. Applying mulch too early (in March or April) can be counterproductive, keeping the coolness in the soil instead of the warmth.

It's important to avoid the tendency to use too much mulch. Never build more than 3” deep. If applied too thickly, mulch will attract rodents and become a breeding ground for fungus. Large uncovered piles of mulch left sitting around in the hot sun will decompose anaerobically and will become toxic to plants once applied (so plan deliveries and yard work accordingly).

Do not create a 2-foot “mulch volcano” around your trees. It may look appealing, but if you cannot see the natural flair that extends from the bottom of the tree trunk to the soil line, you are suffocating your tree. The buried portion of trunk will decay, and the rotting bark becomes an active breeding ground for disease. Instead, apply 2-3 inches around the roots in a circle around the trunk – but not touching it. This will look good AND protect the tree from lawnmower injury.

Shredded bark mulch should be applied in late fall and mid-spring. Wood chips usually need to be replaced every three years. Pine needles can be used around ericaceous (acid-loving) plants such as blueberries and rhododendrons. Pine needles also make a nice winter mulch, as do discarded Christmas tree branches and wreaths.