MULCH

What's it all about?

Bulletin #TP2620

Horticultural Observations for Healthier Landscapes

Would you like to have healthier plants, better soil and use less water? Regular use of various mulches can give you all this and more.
What, exactly, is mulch? Mulch is organic matter from salvaged plant material. Some mulches are at least partially composted, while others are not (shredded bark.)
The mulch which has not been composted will then used as a protective covering placed around plants to prevent evaporation of moisture, freezing of roots, and weed growth.
Composting is the process where the organic material receives a nitrate starter, and then is put into a pile (or a bin), where it will begin to create microbial life. These microbes break down the structure and compositio0n of the organic material. This process creates heat, and the heat in-turn, kills off weed seeds and insects. This then makes the composted material useful as a planting mix to be added into a planting hole. Once composted the organic material is generally not refered to as mulch anymore. Planting Mix or Potting Soil would be examples.

Mulch can be coarse or fine and even consist of rocks in some landscapes. Mulch is for surface applications only, while compost can be worked into the soil.

Benefits

Regular use of compost-mulches helps drainage and improves the soil. Most compost mulch releases natural humic acids when broken down by soil microbes. These acids neutralize alkali deposits frequently found in our drought prone native soils and make nutrients more readily available to plants.

As a surface cover Mulch also helps cool the soil while reducing evaporation during the hot summer months, while isolating roots from the cold of winter nights.
Fine grade mulch will more rapidly decompose and add humic acids, but it is lighter and more prone to blow away if put in windy areas. Bark comes in "Fine", "Medium" and "Large" sizes. Choose the one that is appropriate for the area being used, and is most appealing to you.
Landscape 1/4" to 1" Rock is also considered mulch. It does help reduce evaporation to a degree, but does not really provide thermal protection from cold. Used in conjunction with pre-emergent herbicides (see Bulletin on Pre-emergents) Mulches like bark and rock are highly decorative in the landscape and can be a low maintenance option for weed control and beauty.
Here are examples of the most common mulches normally used in the Coastal, Inland and Desert Southwest:

VARIETIES

◊ Planting Mix (partially composted)

◊ Compost & Top Dressing

◊ Bark

◊ Shredded Bark

◊ Bulk or bagged rock

◊ Saw Dust

Standard Planting Mixes are composted to the point where seeds and insects have been sterilized, but still have enough "green" matter to help create improved microbial activity and so enrich the soil. It is free of sewer sludge and breaks down naturally, over time. When used as a surface mulch; is best when applied as a 2 inch layer in order to prevent weed growth. Refreash this mulch annually in the spring.
When mixed into the soil upon planting, this product will aid in assisting the roots to grow out from their initial pot size. Vital for survival! Mix it with landscape soil to get all your plants, flowers and vegetables off to the best possible start. Do not use solely to surround new plants, as the excessive microbial action will rob the roots of needed nitrogen.
(top)

Compost and Top Dressing are fully composted, humus-based products that give a rich color to the soil surface when used as mulch. They also break down naturally when used as surface mulches and release beneficial humic acids. These products can also be used as seed covers and soil amendments. Apply 1 or 2 inch layer in spring and fall to provide maximum benefit to plants.
(top)

Bark mulches insulate the soil from heat and cold as well as control evaporation. Coarse, medium and large bark mulches are especially useful in high-wind areas since they aren't likely to blow around like fine-grained products. Apply a 2 inch layer around plants and in shrub beds. Do not mix bark mulches into the soil. They remove nitrogen during the composting process and can cause plant stress. Scatter fertilizer on top of the bark when feeding your plants. Then water it in. It will speed composting while providing proper plant nutrition.
(top)

Shredded Bark Because this type of mulch is produced as a "stringy bark", it does a superior job of insulation (compared to larger bark), while not blowing away as easily as the medium and fine bark. Shredded Cedar bark repels insects. Replenish spring and fall to maintain repellant ability. Shredded Redwood breaks down more slowly, so it can also be used as a soil mix without creating excessive microbial action. Apply a 2 inch layer around plants and in shrub beds. Scatter fertilizer on top of the bark when feeding your plants. Then water it in. It will speed composting while providing proper plant nutrition.
(top)

Bulk or bagged rock is a decorative landscape product that doubles as mulch by reducing evaporation from soil in covered areas around desert shrubs, trees and cactus. Rock is normally applied in 1 to 2 inch layers. Since it is highly heat reflective, be careful when using it around traditional plants. Leave a 2 or 3 foot circle around those plants and use bark or humus-based mulch instead. If using rock over a large surface area, keep in mind that sandstone rock decomposes into soil rather quickly, while quartz rock does not.
(top)

Saw Dust & Straw are frequently used as mulches by the home gardener. If using these materials, be sure to keep them out of the soil structure as they remove nitrogen while undergoing the natural composting process. This can cause severe plant stress.
(top)

Home Made Compost Consider building a composting bin (wire fencing works well). Add leaves (avoid using leaves from diseased plants) and clippings. Sprinkle with high nitrogen fertilizer like Ammonium Sulfate (21-0-0). Water and turn the pile over every 2 weeks or so. You'll have a fully composted mulch in about 6 weeks which will be fine to use around your flowers, trees and shrubs.
(top)