For correspondence that is specific to Brenda, feel free to email her directly at lazygardener@sbcglobal.net. 

MULCH CORNER                                    

BY JOHN FERGUSON

NATIVE MULCHES

Last week we talked about Redwood mulches available in Houston area and along the Gulf Coast. This week we are going to look at the best type of mulch "Native Mulch".

For years gardening experts have claimed that this was the best mulch of all and scientific research has backed them up. "Native" mulch is made from recycled fresh green tree and brush material that was recently alive and comes directly from a grinding operation. The Texas Association of Nurserymen (TAN) recognized "Native Mulches" as a separate class of mulches from barks and other materials in their 1997 product directory. Native mulches are available as fresh ground or aged (composted) and in many variations.

Native mulches started becoming available in recent years as society became aware of the importance of recycling brush and tree trimmings instead of burning them or placing them in a landfill. Recent research has found that mulches made from recycled native trees are the highest quality available. They are also among the lowest in cost by offering real value since they are made locally and do not have high transportation costs associated with them.

Local native mulch is produced from a mixture of native trees (primarily hardwoods), conifers, brush and any other species growing in a given area with bark, wood and sometimes leaves included.  Native mulches have a high percentage of buds, shoots, leaves, and cambium bark layers in them. These materials are rich in protein and other nutrients which is why deer and other animals eat them as a food source. These native mulches are many times higher in nutrients than barks. Native mulches encourage biodiversity of beneficial microbes and earthworms in the soil and feed plants as they decompose.

Years ago consumer awareness was the only negative, since the appearance is different than pine bark or shredded hardwood bark. However as these mulches have become more available this perception has changed. Studies and market acceptance have shown that most people prefer the native mulch since it actually looks more natural than barks or other alternatives.

Composted or aged Native Mulch?

Native mulch that is aged or composted first before application is of the highest quality. The heat generated during the composting process kills any pathogens and weed seeds that might have been present. The composting process also concentrates the nutrients contained in the raw material and stabilizes nitrogen.  Additionally, the composting process breaks down the lignin and cellulose contained in the raw material rendering a less attractive home for termites and many pathogens after it is applied. The composting process allows very high levels of beneficial microbes to develop and grow in the mulch increasing its value.

Screened composted native mulch is also an excellent amendment to use in soil mixes as it supplies energy to the soil (stored in its chemical makeup) in the right form for beneficial soil organisms to use. Grinding and screening (particle size) will determine the appropriate usage. A two year study from Texas A&M University (TAMU) has found that native mulch and compost out performed all other erosion control methods. It was also the lowest cost! Research in Florida has confirmed TAMU's work. Research at the Ohio Agricultural Research and Development Center has found that plants grown in substrates rich in biodegradable organic matter (such as found in Native mulches) support microorganisms that induce systemic resistance to disease (American Nurseryman, October 1, 1997).

As a bonus for those in the South dealing with imported fire ants, using a quality composted native mulches may reduce mound density. Many landscapers, gardeners and others have observed and reported a reduction (not elimination) in the number and size of fire ant mounds on areas where composted native mulches were used. It is believed that the native mulches increase the density of organisms that attack and prey on the fire ants reducing their numbers. This has not been confirmed by rigorous research and would be an interesting area of study for our universities.

In general, a 3-4" thick layer should be used on ornamental beds and 4-6" layer around trees and shrubs. It comes in many formulations and sizes. It is sometimes blended with shredded hardwood bark to obtain a familiar appearance (lowers quality) or with compost to increase the quality even higher. It has been used as a potting media in container grown plants, to root cuttings and often works better than bark for many species of plants.

General benefits: Economical, the composting process concentrates nutrients and stabilizes nitrogen, the heat kills weed seeds and pathogens, improves plant and soil health, sets up quickly to resist blowing or washing out, reported to prevent many plant diseases, encourages microbial biodiversity in the soil, reported to increase tree and plant growth rates. Subject to less freight cost and less transportation that causes pollution hence much more environmentally sensible. The usage of native mulch also saves valuable landfill space or air pollution from burning since it is made from recycled materials. 

Using native mulch also helps reduce greenhouse gasses.  When organic materials are placed in a landfill they undergo anaerobic decomposition producing methane which contributes 23 times more to global warming and some nitrogen oxide which contributes 200X more than carbon dioxide.  Also since native mulches are made from recycled materials they qualify for points in the Sustainable Sites Initiative (future LEED landscaping guidelines).

Note:  Course ground and unscreened composted (aged) native works best from a physical, chemical and biological perspective. However, a screened version is more cosmetically appealing and works better as a soil amendment. Sometimes available in a double ground form that looks similar to some shredded barks.

JOHN'S TIP OF THE WEEK

A question we often get asked is "Can I use the wood ash from my fireplace in my garden?"

The answer is a qualified YES.  Wood ash has a lot of minerals (plant nutrients in it)   however it is very alkaline and too much will change the pH of your soil.  A trick I use is to collect the ash from my fireplace and place the ash into a 5 gallon bucket with a lid on it to keep it dry. 

When there is a breeze and just before it rains, I remove the lid and use my electric blower. I aim the airstream over the bucket and slowly lower it until it starts sucking out the ash and scatters it into the wind.  Note: Do not aim the airstream directly into the bucket or it will get all over you.

The wind will carry a very fine dusting of ash all over the yard. The rain (or sprinklers) will wash the ash into the soil.  The minerals are returned to the soil where the microbes will make them available to the plants.  The later of ash is so small per square foot that it does not affect the pH of the soil. 

The next time I need to get rid of ash I wait till the wind is blowing from a different direction so eventually the whole yard is covered.  I have been doing this for years with great results.

EDITOR'S NOTE: 

We routinely receive lots of questions about diatamaceous earth. As a result, John decided to take a shot at covering the topic in brief.  

DIATAMACEOUS EARTH (D.E.)

Diatomaceous earth (often abbreviated D.E.) comes from a soft sedimentary rock deposits called "Diatomite".   It is a soft very fine grained rock, rich in silica that is composed of the remains of fossilized diatoms.  Deposits of diatomite are found all over the earth and range in color from white (very pure) to buff, grey and occasionally black.

The deposits were formed by the accumulation of microscopic single celled aquatic plants called diatoms, a form of algae.  Their external skeleton is composed of amorphous hydrous silica (SiO2,nH20) known as opal. They range in size from one micrometer to one millimeter but most are 10-200 micrometers in diameter and they occur in many shapes.

Diatomite is chalky and very light with high porosity, almost chemically inert hence it is very useful in making cement and for use as a filtration medium. Raw dry D.E. can absorb 1.5 to 3 times its weight in water. Processed D.E. can absorb up to six times its weight in water.

Diatoms are single cell aquatic plants that live in fresh or salt water and use silica (quartz mineral) to form their exoskeleton.  When these plants die they settle to the bottom and can form thick layers of sediment that over geologic time becomes diatomite.

The raw rock deposit is refined by crushing, drying, size reduction and calcining depending on the application.

Its name came from its usage as a stabilizing agent for nitroglycerine when making dynamite, hence the name Diatomite.  Its two largest uses are as a filtration media for swimming pools and as a insecticide (swimming pool D.E. does not work as a insecticide as it is processed differently) .

When processed as a non-toxic insecticide, D.E. absorbs lipids away from the outer waxy layer of an insects exoskeletons causing them to dehydrate. Must be uncalcinated ( not heat treated) and be less than 12 microns in size. Spiny diatoms work best for this application. In addition to dehydration D.E. gets caught between their exoskeleton joints and as they move it acts like little razor blades and cuts them up. It must be kept dry to work hence one must reapply after a rain. D.E. is effective on slugs and snails, bed bugs, ants, earwigs, cockroaches, silverfish, crickets, fleas, millipedes, and  centipedes.

Other applications include; filtration for beer, wines and greases, absorbents, toothpaste, pet litter, metal polishes, high temperature insulating material, sound insulation, paints, plastic products and cement. Medical grade D.E. is also used for a de-worming in animals and humans.