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We often mulch our garden beds, but do we ask ourselves "why"?

Most people will tell you it is to control weeds and conserve water, but that is really only part of the advantage to mulching. When correctly applied, mulch has many beneficial effects on the soil and thereby the plants growing in that soil.

Yes, mulch does keep down weed growth and conserve water but it does sooo much more. By applying mulch, we mimic natures seasonal shedding of old leaf growth. The roots of a plant within the top 8-12 inches of soil surface are responsible for the majority of water and nutrient uptake. Deep roots serve more as anchors. With a layer of organic mulch, soil temperature and moisture content remain more stable, reducing temperature and water stress on these important surface roots. Earthworms are attracted to a mulched environment. They are like little digesters, eating organic matter and returning it to the soil in a form that plants eat. No commercial plant food is as beneficial as "worm manure". Earthworms also aerate the soil increasing water penetration and drainage. Earthworms and mulch will increase the water content in sandy soils and increase the drainage in compacted and clay soils.

Mulch is also home to vital microorganisms of bacteria and fungi that aid in a plant's ability to utilize soil nutrients. Healthy soil is the key to thriving plants and a healthy soil is alive with beneficial microorganisms. Without these mini creatures, plants would need a continuous source of water soluble fertilizers and artificial disease controls in order to survive. Bacteria and fungi break down organic matter into nutrient forms that plants are able consume. Certain fungi attach themselves to the roots of a plant and feed off the plant's fluids while at the same time significantly increasing the root zone of a plant with it's own extensive root system. Plants grown with these fungi are significantly healthier than those without them. Beneficial bacteria and fungi also keep pathogenic microorganisms in check, reducing the need for artificial disease control.

There are many choices when applying mulch, first, whether of not to lay down weed barrier fabric under the mulch. Fabric is a good idea under a stone mulch but stone mulches do not have all the benefits of an organic mulch. My personal opinion is to lay down newspaper or cardboard under organic mulches. In a short time, paper breaks down but not before it has smothered most perennial weeds. Weed barriers can also inhibit water penetration and interfere in the breakdown and incorporation of organic matter by earthworms. When weed seeds land in a mulched bed and then germinate, the root of the weed does not grow through the weed barrier but weaves in and out, making removal a project -good luck-.

There are many choices for an organic mulch. Mulch obtained from the dump is inexpensive (free!), but should not be used near a building because the high wood content can attract ants or termites. A good quality bark mulch does not need any pesticides and options are hemlock, cedar, pine, hardwood or blends. All give you desirable effects but a blend of hard and soft woods gives better nutrient composition than a single bark source. Cocoa seed hulls are a wonderful soil mulch and enhancement. Cocoa is more expensive per cubic foot but only needs to be applied at half the rate of bark mulches. Straw is another good mulch but be careful that you are not laying down hay. Straw is what is left after grain seed has been harvested from the stalk. Hay is the complete stalk, including seeds, which would be more than happy to germinate in your garden. Finished or half-finished compost (weed-free!) makes a fine mulch or topdressing especially under fruit trees or in the vegetable or flower garden. Fall leaves or pine needles are another mulch that is very nice around berry bushes and other acid loving plants. I have also used my own ornamental grass (without the seed heads) as a mulch.

Remember, most weeds come from seed that have been blown or dropped by birds into your gardens. In order for mulch to be effective it must be top-dressed on a yearly basis. The dressing will block sunlight that the seeds need to germinate. Also, seeds remain viable for years so that if the mulch is disturbed and seeds are exposed to the sun, they may germinate. As for fertilizing, most plants that are in an organically mulched bed will have very little need for additional fertilizers and should only be fed after a soil test. One important point to remember is that mulch should never be heaped against the trunks of trees or shrubs. The bark on the trunk is susceptible to decay by microorganisms and poor plant health or death can result.

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