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Much to chew over before mulching

Jessica Walliser
In this vegetable garden, the paths are mulched with straw and the veggie beds are mulched with leaf compost.

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Friday, April 19, 2013, 8:57 p.m.

The soil has finally dried out a little and the weeds have not yet begun their yearly onslaught; a combination that means mulching time has finally arrived. Mulch is any product that is applied to the soil surface to suppress weeds, stabilize soil temperatures, and stave off moisture loss. There are many different mulches on the market, each of which have their own positives and negatives.

Here is the skinny on a few popular mulching products.

Aged manures: I use manure as mulch on my perennial gardens and vegetables. In order to avoid possible pathogen exposure, be sure any animal manure you use is fully composted and a minimum of a year old. And use only manures from animals with a primarily vegetarian diet. Think horse, cow and sheep. Be warned, though, that manure can contain a lot of weed seeds and always wear gloves while working with it. The nutrient content and pH of manure depends on the type of animal and the bedding used to house them. In general, animal manures contain small amounts of nitrogen, potassium and phosphorous, as well as many trace nutrients.

Compost: A personal favorite, finished compost is useful for many different reasons. It's always available from either your own pile or for purchase, and it's often quite affordable. Compost adds more organic matter back to the soil faster than other products and it often comes with a slight nitrogen charge to boost your plants. I also like how easily it spreads since its fine particles sift down around the plants rather than burying them. The pH of compost averages between 6.0 and 8.0, though its ingredients do impact the pH of the finished product. On average, compost contains 50 percent organic matter and moderate amounts of both macro- and micro-nutrients. Composts containing biosolids (sewage sludge) can be too high in nitrogen and should be avoided as a mulching product to prevent nitrogen burn.

Straw: I use straw in my vegetable garden because it's inexpensive, easy to apply and takes a season or more to fully break down. I use it to mulch the walkways and larger vegetable plants like tomatoes and peppers. It also works well beneath cucumber and melon vines, where it helps keep the developing fruits off the soil and away from pests and diseases. Spreading a few layers of newspaper beneath the straw serves to prevent weeds even more, especially in the pathways.

Shredded bark or hardwood: Though dyed bark mulches should be avoided as they are often made from possibly contaminated recycled wood products and do not break down to add organic matter to the soil, uncolored shredded wood products are a great mulching option. I like to use shredded bark around my “woody” plant material like trees and shrubs. Many landscape suppliers have single-, double-, and even triple-shredded wood products. While single-shredded lasts longer, it's coarser in appearance than the finely graded triple-shredded mulches. Choose whichever suits your gardening style. Be warned, though, that shredded bark mulches are in a fresh state and, unlike finished compost, they are actively decomposing. As wood-mulching products decompose they do indeed “steal” a little nitrogen from the soil and, though this nitrogen is eventually returned when decomposition is complete, it can cause a temporary lack of nitrogen in the top few inches of the soil beneath. Not a big deal around deeper-rooted trees and shrubs, but with more shallow-rooted perennials, annuals and veggies, this may cause a nitrogen deficiency in some plants.

Leaf mold or leaf compost: This type of compost is comprised of a single ingredient: leaves. It can be made commercially from municipally collected leaves or at home from leaves collected on your own property each autumn. Leaf compost is a favorite for its friable, loose texture and lack of weed seeds. Though it is fairly low in nutrients, the amount of organic matter leaf compost adds to the soil is substantial. I use it over my entire vegetable garden as well as in many of my perennial beds. It was once thought that the types of leaves used to make the compost influenced the finished product's pH and nutrient levels, but some recent studies have confirmed that the pH and nutrient content of leaf compost is fairly stable, regardless of what types of leaves were used in its creation.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is

Send your gardening or landscaping questions to or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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