Mulching Trees & Shrubs

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Back in the 70's Someone had a bright Idea!

According to the dictionary, mulch is defined as "A protective covering as of leaves, manure, or hay, placed around plants to prevent evaporation and freezing of roots". Today other types of mulch being used include: Bark chunks, usually from pine trees; Wood chips from tree trimmings; Cedar, fir, and pine chips from logging operations; Wood fines... which are tiny wood chips and dust from screening larger wood chips; Compost and pine straw (needles) are also used as mulch. You can even purchase "Painted Mulch" which is simply painted wood chips in various colors.

Back in the early 70's someone had a bright idea to cover bare soil in the landscape with black plastic and put either mulch or rock over the top of it in order to stop weeds from growing. Then they would cut holes into the plastic to plant a tree or shrub. Well, weed growth was suppressed for a while. As time went by dust and dirt blew in on top of the rocks and then the weeds seeds blew in too! Sure enough... with a little bit of moisture the weeds started to grow on top of the plastic, in amongst the rocks. After a few years the plastic starts to get holes in it. Now the weeds are growing up from underneath and on top of the plastic. So much for controlling weeds! After a decade or so the rock, plastic and weed combination starts looking pretty bad.

Solutions to this bad appearance included covering the old rock and plastic with a new layer of plastic and rock, creating the "Sandwich" affect... or pulling in all out back down to bare soil and starting over. Once the old rock and plastic are removed low and behold the tree and shrub roots are found growing right on top of the soil just under the plastic! It's no wonder the trees and shrubs often died from drought and freeze injury. When mulch was placed on top of plastic instead of rock, weed control was much worse. Mulch eventually decomposes into compost... and compost really grows healthy weeds!


Seeing that plastic was not a long term solution

 to weed control, as well as it stopped air and water from penetrating the soil, somebody invented "Landscape Fabric". The thought here was this fabric would "Allow the soil to breath and allow water to flow through it" as well as keep weeds from growing from under it. Just like it's predecessor... the plastic, dust and dirt blew in as well as the weed seeds. Only now, the weed roots can penetrate through the fabric and latch into the earth below. Trying to pull up a piece of weeded up landscape fabric is like trying to pull a tree out of the ground! It's really stuck in there. Another big problem with the fabric is that due to it's hairy fibers, soil particles adhere like super glue to the fabrics fuzz, cementing it to the ground, making it nearly impossible to remove! And once you do pull it up... there are tree and shrub roots right under the fabric.

There are places where fabric is useful such as, small places next to buildings, narrow parking lot islands, under gravel driveways and paths, etc. Try to avoid using fabric in large areas where you plant to grow trees and shrubs. Plastic is also useful for areas where you are trying to exclude water from penetrating the soil. Next to a building foundation is a place to use plastic as a method to deter water.

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The best way to use organic mulch

in tree, shrub, flower beds and gardens is to put the mulch directly on top of bare soil. When mulch is in contact with soil it slowly decomposes, adding organic matter to the soil. In most of Colorado and the Denver Metro area, we lack organic matter in the soil. Organic matter in the soil holds water, provides pore space for oxygen to enter the soil, holds essential nutrients, helps lower soil pH, and feeds soil organisms that release nutrients to plants.

Mulch helps suppress weed seed germination, but will not stop weeds from growing up through it. Manual and chemical weed control with Roundup is necessary maintenance to keep weeds in check.

Key tips on getting the most from Organic Mulch

  • Mulch is amazing at retaining soil moisture and it protects against extremes in temperature.
  • As mulch decomposes and "feeds" the soil it needs to be replenished with new mulch.
  • Do not put mulch in direct contact with tree trunks and shrub stems. Because mulch holds water it can rot the base of trees, shrubs and other plants. Leave 6" of space between trunks and mulch.
  • Another type of mulch that often is discarded as trash is pine and spruce needles that fall naturally from the trees. If space allows leave this material on the ground!

The type of mulch you use is all a matter of choice. I use locally produced, recycled wood mulch in all of my bed areas. It is cost effective, looks good, doesn't blow or float away and is produced from local tree waste. No forest trees are logged to produce it. But that's just me. What type of mulch do you like?