Mulch is a generic term that applies to any material that when applied to soil:

• Improves soil structure, water penetration, aeration, and drainage.
• Insulates the soil surface, keeping it warmer in winter and cooler in summer.
• Reduces surface evaporation and the need for frequent watering.1
• Promotes faster landscape plant growth by eliminating competition from grass roots for water and nutrients.2
• Protects tree trunk and surface roots from mowers and string trimmers.
• Provides for ease of lawn maintenance.
• Provides an aesthetically well-cared-for landscape appearance.

There are two types of mulches: Organic and Inorganic

Organic mulches include wood chips and bark such as cypress, pine needles, straw, nut shells, compost mixtures, and leaves. Organic mulches offer the advantage that they can reintroduce nutrients and improve soil tilth. However, the disadvantages are that:

• The nutrients returned to the soil during decomposition may actually promote the growth of weeds.3
• They are light weight and are frequently washed or blown away by storms.
• They are easily compacted and hinder water and air movement into the soil.2
• They quickly fade in color. A study of six organic mulches showed that cypress, melaleuca, eucalyptus, pine straw, pine bark, and Gainesville Regional Utility (GRU) mulch all began to fade within one year.5
• Some microbes that decompose the mulch also absorb nitrogen which can result in a deficiency of this essential nutrient in the landscaping plants. Therefore organic mulches are only recommended where fertilizers are unavailable.4 One study concluded that the allelopathic properties of some organic mulches may actually inhibit the growth of landscape plants.5
• They decompose rapidly and need replenishing to function effectively. This is labor intensive and expensive.2
• They provide arthropods and/or invertebrates with food, shelter, and moisture which they need for survival. Fungi, algae, or bacteria that proliferate in mulch, including bagged mulch sold in garden centers or nurseries, serve as an additional food source for many invertebrates. Applying organic mulches to landscapes, particularly near home and building foundations, may attract nuisance and/or structural arthropod pests such as mites, centipedes, millipedes, earwigs, carpenter ants, pillbugs, sowbugs, earwigs, spiders, rove beetles, ground beetles, and termites as well as rodents such as rats, mice, and voles. Arthropods and other invertebrates may seek out more favorable conditions in homes when outdoor temperatures and moisture conditions become less hospitable.6
• They are a source of exotic pathogens. Chipping of wood palettes, dunnage, and other wood–based packing materials for sale as mulch is a common practice in North America. Several reports from a recent symposium that addressed the issue of international trade of wood and wood products focused on the increase of the importation of exotic pathogens and other pests. The results of this study suggest that infested wood chip mulches are a source of inoculums for plant pathogens. Infested mulch may allow some fungal pathogens to survive for prolonged periods until environmental conditions and horti-cultural practices favor infection. Thyronectria austroamericana, a plant pathogenic fungus, can remain viable for well over 2 years after infected plant parts are removed from the host plant. Thus, the risk of introducing exotic plant pathogens via the importation of wood-based mulch can be increased by the use of this material for landscape mulch. The findings from this research may justify stricter regulations on organic mulches.7
• Some municipalities offer free mulch to their citizenry to save valuable landfill space. However, frequently this mulch is derived from diseased trees which support the growth of numerous microorganisms and pests and contain weed seeds.7
• Broad spectrum pesticides such as dursban, diazinon, malathion, rotenone, pyrethrum, and sevin kill many kinds of insects, good and bad.2

Inorganic or inert mulches include decorative stone and gravel, lava rock, pulverized tires, plastic sheeting, and geotextile fabrics. The advantages to inorganic mulches are:

• They break down slowly and do not have to be replenished frequently.
• They are usually heavier than water and are not easily washed away by rainstorms or blown away by windstorms and thereby reduce soil erosion.
• If applied properly they prevent the growth of weeds.
• They are uniform in color and the color is slow to fade.5
• They can incorporate natural elements into the landscape which are more aesthetically pleasing.
• They allow better landscaping with native plant species.2
• They are not easily compacted or hinder water or air movement into the soil.
• Trees growing in inorganic mulch have larger stem calipers and result in greater leaf dry mass than those growing in organinic mulches. This is believed to be the result of the plots covered by organic mulch treatments having significantly lower soil temperatures (mean 74.1 deg. F) than plots treated with mineral mulches (mean = 78.6 deg. F) 9 thereby extending the growth season.8
• They do not mold.9
• They are less attractive to termites.10
• They do not constitute a fire hazard. Many commercial and public facilities no longer permit smoking inside as a result of today’s laws and policies. Cigarette and cigar smokers often discard lit smoking material into the landscaped areas as they enter a building, thus causing the potential for mulch ignition. As people move from smoking areas outside the building to areas within, discarded cigarettes smolder and may set the mulch on fire. Mulch fires, in turn, can place frame construction buildings at risk. The risk of a mulch fire is, perhaps, more common than one might expect. The Ohio State University Agricultural Technical Institute campus in Wooster, Ohio, U.S., had an incident in fall 2000 where smoldering mulch betrayed a subsurface mulch fire. In Columbus, Ohio, a mulch fire was credited with severely damaging a building. Scioto Dublin High School in Dublin, Ohio, was closed as a result of a mulch fire that contaminated the air-handling system in the building. An improperly discarded cigarette ignited the landscape mulch and then spread into the crawl space beneath the structure, damaging a Brookhaven National Laboratory structure. Problems such as the above have become enough of a nuisance at The University of Maryland that their Environmental and Safety Department developed a mulch fire standard operating procedure (Mulch Fire Standard 2002).11

Soil Acidity and Calcium Deficiency

Soil acidity is one of the most important factors effecting plant health. Soil acidity refers to the concentration of active hydrogen ions (H+) in the soil. It is measured by an index called pH. A pH of 7 is neutral. A pH below 7 indicates acidity and a pH above 7 indicated alkalinity.12 Soil acidity is extremely important as it influences the chemical form of many elements as well as microbial processes which greatly affect plant health and the absorption of minerals and nutrients.2 In general most Florida soils are acidic, with a pH around 4.5.12 The ideal pH for South Florida garden soils ranges between 5.5 and 6.5.13 Acidic soils at pH 5 and lower often contain appreciable amounts of aluminum (Al) and manganese (Mn) which are toxic and detrimental to plant growth.14

One major advantage of our product is that it is almost pure Calcium Carbonate (CaCO3). This is the only active ingredient in Tums Antacid and the best compound for neutralizing acid. In fact, the effectiveness of all other liming agents are expressed in terms of Calcium Carbonate Equivalents (CCEs).14

Soil pH tends to decrease (become more acidic) with repeated use of nitrogen (N) fertilizer. The sandy flatwoods soils in South Florida tend to have low clay and organic matter content (< 2%) and generally low buffering capacities.12 In acid soils with pH less than 5, the availability of boron (B), molybdenum (Mo), magnesium (Mg), potassium (K), phosphorus (P), sulfur (S), and calcium (Ca) is reduced and nutrient uptake and forage production is severely reduced.12, 14 Additionally, under low pH (< 5) plants are susceptible to yellowing and damage by soil-borne insects. Research and surveys conducted throughout south-central Florida have shown a link between declining soil pH and severity of mole cricket-induced bahiagrass decline.12

Calcium deficiency and root injury is observed at pH 5 and lower. At these low levels, lateral root development is suppressed and in some cases root tips are killed. At low pH and calcium concentrations, damage to root membranes is accentuated. An important function of calcium in the plant is with the formation of cell walls. Since calcium is immobile within the plant, the fruit continues to grow but the growing tip is soft and dark due to poor cell wall formation.14 In cases of calcium deficiency, growth stops and roots are ofgten clubbed (swollen). Upper leaves do not expand and are frequently curled up. The plant is generally stunted with a gummy secretion oozing from the leaves. Death of the terminal shoot (tip) occurs in advanced stages, althoughshoot tip die-back can occur without chlorotic foliage as a main symptom.2 The following pictures illustrate tomato and watermelon blossom end rot due to calcium deficiency.14

Cypress Mulch

In recent years cypress mulch has grown in popularity. However, one common misconception about cypress mulch is that it discourages the profileration of termites which cause approximately $5 billion in structural damage annually in the United States alone.6 It is only the cypress heartwoods that are repellent and toxic to termites. Today’s cypress mulch is harvested from young trees with little or no heartwood.10 Subterranean termites have has been reported to consume cypress sapwood mulches. A series of no-choice food experiments were conducted to determine whether termites would consume cypress sapwood, eucalyptus, pine bark, straw, and utility pruning mulch. The results indicated that termites consumed all of these but had a preference for mulches with higher nitrogen and phosphorus concentrations which would otherwise return to the soil and be absorbed by garden plants.10 Studies also showed that subterranean termites forage for food as far as 250 feet from their colony.10

It should also be noted that Gulf Coast cypress forests are not sustainable. A scientific panel commissioned by Louisiana Governor Kathleen Blanco in 2005 estimated that 70-80% of Louisiana’s cypress forests could not regenerate. Many factors, such as the presence of levees along the Mississippi River and the construction of spoil banks fro logging operations and oil and gas drilling, combine to create stagnant and salty swamp ecosystems that are unable to sustain cypress. Once cut these areas will not regenerate and cypress swamps serve as very effective physical barriers in the protection of the Gulf Coast from hurricane surges and in saving property and lives whenever major storms strike the coast.15

Which Mulch is Best for You

The nursery and landscape industry is fortunate to have a wide variety of mulch materials to choose from, but in the final analysis, cost, appearance, and ease of maintenance generally dictate which mulch is best for you.
This is why our product at Shell Scape of Florida can save you hundreds of dollars compared to your standard mulch.

1. Florida Gardener’s Guide, Tom MacCubbin and Georgia B. Tasker, Cool Springs Press, 1997

2.Your Florida Landscape: A Complete Guide to Planting and Maintenance, Robert J. Black and Kathleen C.Ruppert, University of Florida/IFAS Cooperative Extension Service, 1998

3. Mulch 101: The Art of Selecting the Perfect Garden Mulch! Eden Makers Blog, October, 2008

4. Mulches for Home Grounds, Colorado State University Extension, J.E. Klett, January, 2007

5. A Comparison of Landscape Mulches: Chemical, Allelopathic, and Decomposition Properties, Mary L Duryea et al, Journal of Arboriculture 25(2): March, 1999

6. Mulches and Living Organisms, Kansas State University Agricultural Experiment Station and Cooperative Extension Service, MF-2900, September, 2009.

7. Tree Pathogen Survival in Chipped Wood Mulch, Ronda Koski and William R. Jacobs, Journal of Arboriculture 30(3): May 2004

8. Effect of Organic and Mineral Mulches on Soil Properties and Growth of Fairview Flame Red Maple Trees, Jeffery K. Iles and Michael S. Dosmann, Journal of Arboriculture 25(3): May, 1999

9. Organic Mulch Vs. Inorganic Mulch for Gardening, DoItYourself.com

10. Will Subterranean Termites Consume Landscape Mulches?, Mary L. Duryea et al, Journal of Arboriculture 25(3): May, 1999

11. The Ease of Ignition of 13 Landscape Mulches, Larry G. Steward et al, Journal of Arboriculture 29(6): November, 2003

12. Soil pH and Liming Issues Affecting Bahiagrass Pasture, M. Silverira et al, University of Florida IFAS Extension. Publication No. SL292/SS505

13. The Art of South Florida Gardening, Harold Songdahl and Coraleee Leon, Pineapple Press, 1996

14. Soil Acidity and Liming, Internet Inservice Training, Clemson University Extension Service, Dept. of Crop and Soil Environmental Science, March, 1999

15. Understanding the Environmental Impacts of Cypress Mulch, Southeastern Louisiana University Lake Pontchartrain Basin Research Program, August, 2007