By Nancy Penrose

Spring is a great time to ensure the continued health and beauty of your landscape by mulching, pruning and fertilizing. If you have trees on your property, mulching should be at the top of your list of tasks.

Mulch is material applied to the soil around a plant. The word is believed to come from the Middle English word “melsche” which means soft and Old English melsc (mellow or mild).

Mulching has many purposes. To start with, it conserves water by slowing down evaporation. Because the soil won’t dry out as quickly, less watering is needed. However, you also need to be careful that the mulch isn’t actually blocking water from entering the soil.

Mulch also protects the soil and plant roots from the sun. In addition to reducing heat stress, the soil will remain cooler for a longer period of time. Cooler soil means plants won’t prematurely leave their dormancy.

Another benefit of mulch is that it can prevent plant damage from lawn mowers and similar types of equipment. Mulching also stops the growth of weeds, which can save you time in the garden. Mulch can even be used to get rid of small plants that are no longer wanted by placing it directly on top of the greenery

There are many different materials used in mulching, including shredded bark, wood chips, leaves, grass clippings, straw, pine needles, pecan shells, cocoa hull, sawdust, peat moss, manure, compost, cardboard, newspaper, river rock and gravel. Non-organic materials include plastic sheeting and rubber from tires.

Mulch also comes in colors. The dye is water-based and considered non-toxic.

Organic mulches will decompose as time goes on. As tree bark decays, it can absorb nitrogen from the soil. One way to prevent the loss of nitrogen is to add fertilizer to the soil.

Mulch is usually spread by hand around the plant. Depending on the amount of mulch that is needed (and type of mulch you are using) you may need to load it into a wheelbarrow. When organic materials are used, the mulch should be at least 6 inches in height.

If mulch ends up on your grass, remove it immediately. Otherwise, the grass underneath it will die.

When mulch that contains a large amount of nitrogen isn’t rotated, decomposition can speed up, causing toxicity. Over time, the decay can change the woodsy aroma of the mulch to the smell of ammonia, vinegar and sulfur. The smell of this anaerobic (sour) mulch will dissipate when the mulch is exposed to air. Sour mulch placed on soil before the dissipation occurs can damage and even kill plants and trees.

May is usually considered one of the best times for mulching. If you plan on mulching big trees (Seattle area), get tips and advice from a big tree supplier or tree nursery (Snohomish) and make sure they are tree nurserys knowledgeable in big tree care. Identifying trees correctly to understand their particular needs is the best way to avoid mistakes that could damage the health of your tree. A supplier with large trees for sale will know what type of mulch you should use and how to spread the mulch beneath the tree. Always keep mulch at least six inches away from the tree trunk.

Nancy Penrose is owner of Big Trees Inc. (, tree nursery Snohomish, WA, one of the largest Seattle tree nurseries (see inventory at, specializing in tree transplanting. See our video at