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Mulch in Austin - What you need to know

One of the secrets to an amazing low maintenance yard is the proper use of mulch.  It can help reduce weeding, watering, and even fertilization.  In short, it makes life easier.

What is Mulch?

It can be any number of ground covers spread over a planting bed.  What is used, and what it is called varies significantly from region to region across the country.  In some areas when someone talks about mulch, they could be referring to either: rock, recycled rubber shreds, repurposed furnace slag, bark stripped from the logging industry, or any number of inventive or locally available ground covers.

In central Texas, when we talk about Mulch we are usually talking about partially decomposed wood and recycled plant matter.  In other areas, the same product would be called “bark” or “bark dust.”  This all-natural product has a lot of advantages and does a lot of beneficial things for your landscape.

Why is mulch used in landscaping?

Mulch’s primary function is to cover the soil and fill in space.  It is added in a relatively thick layer over any soil that would be exposed.  The exact installation method varies depending on the type.

Nature hates a vacuum.  If there is a blank space, something will grow to fill the space – and plants that colonize empty spaces are almost always weeds.  Weeds grow well in disturbed soils i.e. freshly cleared and prepared planting beds. 

How does mulch stop weeds?

Mulch will stop weeds by taking advantage of some of the laws and rules of mother nature. 

The first is that mulch creates a barrier over the soil that is hostile to plant growth.  Bare soil is the perfect medium for the growth and spread of weeds.  Seeds, blown by the wind or distributed by critters, are looking for a patch of bare soil.  If they cannot reach that soil, they are going to have a much harder time growing.

A good mulch not only blocks the soil, but it also contributes to creating a hostile growing environment.  Natural mulches, like native hardwood mulch, are partially decomposed.  This means that microbes are working to decompose the mulch further.  The microorganisms use the same nutrients that plants rely on to live, meaning they use up the available food, so it is not available for germinating weeds.  This natural process only functions with a thick layer of mulch, with plenty of un-decomposed mulch at the surface.

Why is my mulch disappearing? Where is my mulch going?

Those microbes in the soil are doing much more than hoarding nutrients.  Eventually, they eat up (decompose) the mulch, and then die.  The result is incredibly rich healthy soil, but no mulch.  This rich soil is amazing for plant growth – both intentional and invasive.  If you are not careful, the weeds will explode, healthier than ever.

The beds are natural fertilizer factories, churning out the nutrients necessary for great plant growth.  Eventually, the plants will use up every molecule of that rich humus, and nothing will be left.  It all happens on a microscopic level so that sometimes it feels like your mulch is simply fading into thin air.

The trick is to keep feeding that process.  Keep those microbes working, keep those plants healthy, and keep those weeds out.  The magic number is 3 inches of mulch.  This keeps a layer hostile to plants on the top, and pumps out healthy nutrients at the bottom of the mulch, right were your lovely plants need them.

What else does mulch do?

We have already established that mulch helps keep weeds out, and it generates the nutrients that plants need to survive.  That seems like enough.  (Cue the cheesy infomercial  announcer:) But wait – there’s more!  It helps regulate the moisture and temperature in the soil. 

Sunlight and wind can dry out the soil, removing water through evaporation.  The layer of thick mulch helps keep the soil moist.  This works best with drip irrigation systems, where the water is never exposed to sun or wind, but it will help hold moisture in the soil from rain and sprinklers as well.

That same layer also acts like a blanket and insulates the soil from rapid shifts in temperature.  This is most important in the winter when the temperature drops.  Bare soil, exposed to falling air temperatures and wind, can quickly drop to temperatures that could damage delicate plant roots.  Mulch can keep those delicate plants alive.  Keeping the soil temperatures stable keeps plants alive. 

Additionally, the microbial activity that decomposes mulch generates a small amount of heat.  Some horticulturalists have used large piles of decomposing mulch to keep tropical plants alive through blizzards far up north.  Bananas growing in Idaho? Only with the power of our magic friend! (Though it’s easier to just grow potatoes.)

Why isn’t my mulch Magical like the mulch described here?

A healthy mulch layer does all the things mentioned here, but only if installed and maintained correctly.  It is a natural balance, and it does have its limits and requirements. 

Not all weeds are stopped by this magic stuff.  Weeds like Nutsedge will grow through anything – including solid asphalt and concrete.  Other weeds are good at spreading into a well mulched bed from the edges, avoiding the hostile zone at the top, and making a beeline to the thick healthy soil at the bottom.  Other solutions are needed for these problems, but it does not negate the value of healthy mulch eliminating all the other weeds that could be in the bed.

It also needs to be refreshed regularly and maintained at a thick enough layer to get the natural decomposition engine fired up and running smoothly.  A thin scraping of mulch that barely covers the soil will do nothing other than help the yard look good for a few weeks.  If you put too much mulch down, the same process that stopped weeds will start killing the good plants too.  The trick is a healthy 3-inch layer, maintained by adding mulch to keep the beds topped up once or twice a year.

Also, avoid using weed fabrics under natural mulch.  The fabric stops the rich soil from reaching the plants, and eventually, weeds will take advantage and steal all those nutrients for themselves ON TOP of the fabric. 

Also, make sure you are using good mulch.  Old shredded tires don’t cut it, and some of that dyed stuff from the big box store is barely worthy of the name of Mulch.

What mulches are available in the Austin area?

There are several local, healthy mulch options in our area.  For most beds, sick with the most common stuff.  Native Hardwood Mulch.  It’s good stuff.  Largely composed of decomposed hardwoods, it does not float well and resists being washed out more than lighter softwood mulches like pine mulch.  It is also a recycled product, good for the environment in more than one way.

Another good option for certain conditions is Cedar.  It is mostly made from the local juniperous asheri, so the wood will naturally resist decomposition more than hardwood mulch.  This slows the entire process significantly, making Cedar Mulch effective at stopping weeds in areas without formal landscaping for longer periods.  It also slows down the nutrient benefits of mulch, so it is a poor choice for the average planting bed.

Avoid the cheap dyed chunks of wood sold bagged at the big box stores.  These are usually made of old shipping pallets, chipped, and dyed to look more natural.  These mulches are dead on a microbial level and tend to stop the decomposition process in its tracks.  That’s a bad thing.  The lighter wood floats easily and moves around to where you don’t want it.  It might look good, but it is not ideal. It’s better than nothing but using the right much is going to make life much easier on you AND your plants.

Additional information from our friends at the Texas A&M AgriLife Extension:

(they know Plants AND Texas)

Ten Ways to Make Your Landscape Earth-Kind (Spoiler alert #1 is MULCH!)

How much mulch should I use around a tree? (Avoid a common mulch mistake – Read this)

 

Mulch is often partnered with planting or perhaps sod

Or maybe you want to see a bit about how mulch is made?

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