Some organic mulches come with caveats. Bagged cocoa hulls lend a wonderful, chocolate aroma to the garden, but can be toxic to dogs and cats. And because hay often contains weed seeds, it’s a poor substitute for straw. If you choose manure, always use composted manure rather than fresh manure, which can burn plant roots.
When to use inorganic mulches
Inorganic mulches, such as plastic sheeting, landscape fabric and rubber mulch made from recycled tires, have none of the soil enhancement and few of the water conservation qualities of organic mulch. Regardless, they can play important roles in the garden.
Plastic sheets can be used in the spring to warm up beds quickly and then can be removed at planting time. Some vegetable gardeners even poke planting holes through the plastic and keep it on their plots all season to help suppress weeds. Rubber mulch makes a great surface for pathways and landscape fabric can be used as a sub-layer to keep weeds down on a gravel pathway.
Some of the best mulches are free. Chopped leaves (run them over with a mower), backyard compost, grass clippings and pine needles make ideal mulches, and they’re freely available natural resources in many regions of the country.
How to apply mulch
Add organic mulches to garden beds once the soil has warmed in late spring or early summer. A shallow layer of between five and eight centimetres deep provides an effective barrier against weeds, sun and wind. When applying, keep the mulch away from the crowns of perennials and the stems and trunks of shrubs and trees, where it may promote fungal diseases such as crown rot.