Wednesday, March 6, 2013

Mulching A-Z

  Most of the questions that I receive regarding landscape maintenance are on the subject of mulch. Bark mulch, cedar mulch, cypress mulch, colored mulch, wood chips,......every year there's a new product that enters the market.  The three most common questions regarding mulch are; Which one is the best, which one is the least expensive and lastly, how much should I use.  But before I get into that, let me explain some of the benefits of what I call "tree mulch". I call it tree mulch because it isn't gravel, it isn't rubber and if it isn't specfically labeled "bark mulch", it is usually pulpwood that has been either colored or mixed with compost to give it a richer appearance.
Benefits of mulch (some types provide more of the following than others)
  • They preserve moisture and keep soils evenly moist.
  • They help keep ground temperatures consistent during extreme highs and lows.
  • They dampen the growth of weeds.
  • They keep insects out of the garden.
  • They beautify the landscape.
  • They condition the soil by adding nutrient rich humus to the soil upon decomposition.
  • They work well with spreading plants such as perennials and groundcovers.
  • They are derived from renewable resources.
Before I continue, I should warn anyone reading this who is considering mulching a garden space that they should never use plastic or fabric weed barrier under tree mulch. This has been a false practice by the landscape industry, primarily as a tool to get you to spend more money on the process. The reason behind not using weed barrier is that all tree mulch, whether bark or pulp-wood based, is eventually going to break down organically to dirt (humus). When it does (with bark at a rate of 1" or more per year), the garden plants roots will seek out this nutrient rich soil above the barrier and begin growing out laterally rather than down. Within 3 years, every plant will have its root systems primarily above the barrier and they will easily become subject to drought, winter-kill and dwarfed growth.
The organic breakdown of the mulch and it's entering into the soil is it's most valuable benefit. Weed barrier does not block weeds but rather, it prevents nutrient rich decomposing mulch from entering the soil and promotes shallow root growth!

Types of Mulch and their Benefits

Hardwood Bark Mulch

Hardwood bark mulch is a blend of hardwood pulp wood and hardwood bark. In the earlier years it was all bark and then as recently as ten years ago they began blending it with a 20% mixture of pulp wood. Hardwood bark offers all of the benefits listed above and is the best at suppressing weed growth. It is prized for its rich natural color. It is the best priced product on the market and certainly has the most benefits.

Pine Bark or Softwood Bark

Pine bark is not normally available in bulk. It does come in bags of 25 pounds. Pine bark, because of it's composition, does not break down as easily and provides little value to the garden bed other than its natural appearance. I would not recommend pine mulch nuggets as mulch for a perennial garden. It has its use as an alternative for rock in a japanese style garden that is planted primarily with evergreens and pines of its natural order.

Cedar & Cypress Mulch

The primary benefit of cedar mulch is its aroma. Being light and consisting of primarily pulp wood and very fibrous bark, it tends to dry out very quickly, causing it to turn white and unappealing. Its benefits are moderate compared to the Hardwood bark which is priced at about half of that of cedar.

In the early days of my landscape career cypress mulch was made from true cypress trees harvested from the florida everglades wetlands. Today, because deforestation is destroying florida's wetlands and adding to the deteriorating balance of the florida everglades and other wetlands, mandates have been passed limiting the use of natural cypress when harvested alive. Although most of that which is being called cypress mulch today consistently costs more than any other type of mulch, it is usually not cypress trees at all, but instead a specifically colored-to-match, dyed or stained mulch that is being passed off as natural cypress because of its infamous yellow-gold color. However, because of the recent storms and floods that have been so pervasive in that region, there is a considerable amount of cypress available from downed trees that are being recycled into mulches.
Because cypress is naturally tolerant of moisture, it has been prized for its absorbtion ability and by hence, makes for an ideal mulch in dry climates.  But do not be fooled. I have seen pulpwood passed off as bark and ground-up lumber and pallets dyed with color stains and passed off as exotic brazilian rainforest products in order to attract high-end buyers who oftentimes have a fancy for the exotic. Cypress mulch, if in fact it is true cypress, has no more landscape value to it than hardwood bark but it is twice to three times as expensive.

Colored Mulch

Colored mulches are all the craze as of late. There are plenty of colors to choose from and even blends of two or more colors have been used to make a statement. However, It is generally 30-40% more expensive than bark mulch and has only half of its benefits. Until child-safe dyed mulches were made available, thousands of reports were made by physicians regarding mild poisoning in children and animals. By utilizing naturally derived color enhancers for staining mulch, the producers of dyed mulch now stand behind the safety claims of their products but colored mulches have some other downfalls as well. To begin with, they are 100% pulp wood which, is usually derived from recycled lumber, pallets and tree pulp wood. Because of this composition, they provide little water absorption. Because they break down so slowly or if at all, these mulches provide no benefit to the soil as in the way bark does as it decomposes. Mulches that are colored will fade in color dramatically before they ever break down organically. In most cases, they end up being covered up, layer upon layer until the mulch becomes so thick that it literally starves the plants of air and water. But all is not lost on colored mulches as you will soon see.

How thick should we go with mulch?

On a fresh bed of dirt we recommend 4-5 (un-packed) inches of Hardwood bark. We recommend up to six inches of cedar mulch. The optimum use for colored mulch is to use it in conjunction with hardwood bark. Use 2 inches of colored mulch placed on top of 3 inches of bark mulch. This method provides you with all the benefits of a less expensive mulch with the added benefit of the visual appeal and color selection of the dyed mulches.
When it comes to mulch, bark rules. It's cheaper, more widely available, has the most benefits and can be used as a base for other mulches.
Remember also to use less mulch around ground cover type spreading perennials and never, never, never use weed barrier or fabric.
Happy mulching!

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