Question
Sean,
I live in Houston, Texas. I Recently purchased a new home with new sod.  Our fence along the back of the back yard is a brick wall, per community standards. I am planning on having eight to ten yards of good soil brought in and constructing a six foot wide raised flower bed across the entire width of the Back yard (up against that brick wall). One question that I have is, do I need to excavate the sod back there where I will be building the raised flower bed and, do I need to put down that landscaping fabric before I have the dirt hauled in? If so what kind? What does that fabric do?
Also, obviously this is a large amount of soil. What would be your suggestion as to treat this much soil, as far as aeration, fertilization, etc....?

I know you are very busy, so......
Thank You in advance for your time.

Dwayne Wright
Houston, Texas

Answer
Hey Dwayne,

Whether or not you excavate (or remove) the sod depends on the type of sod and depth of soil you plan to add on top. If the sod is a vigorous grower like bermuda it would take several feet of soil to kill it and ensure it did not come back through your planting bed. If it is a fescue or weaker cool season grass it may only take about 6" of soil to kill it where it won't come back.

However, your best and safest bet is to spray out the sod with a herbicide and then remove it or till it in with your new planting soil.

As for landscape fabric,there are many types of landscape fabric for different purposes. They include geotextiles meant to hold walls and soil in place, filters to separate soil from intruding into adjacent areas, silt barriers, and weed barriers.

For the purposes of this answer I will assume you are talking about the later ...weed barriers.
I personally don't believe in the stuff. There are many types, but the primary function of all is meant to keep out the weeds while allowing your plants to thrive. The basic premiss is that you lay the fabric out on top of the soil of your planting beds and cut small holes big enough to plant your flowers and shrubs through it and then cover the fabric with mulch. The idea being that weeds can not grow through the other areas. These mats are made to stop plants from coming up but allow water to pass through.

In truth, this system works at first ( 1 to 2 years) but then quickly becomes problematic (3 years and ever after). The fault lies in the assumption that weeds are already in the soil. Well the truth is there are certainly seeds already in the soil but many more are dispersed by wind and surrounding plants every year. So what happens is, over time, the mulch on top of the weed mat breaks down and becomes soil on TOP of the weed mat. Also soil washes in and is blown it from the weather. Then the wind dispersed seeds begin to grow in this thin layer of decomposed mulch and soil. The tiny roots are able to penetrate the weed mat. (Note that weed mats are perforated with thousands of tiny holes to let water through but not big enough to let the leaves of plants grow up from below). These roots then go in to the soil below and the weeds continue to grow. Some time later the Gardner tries to pull up the weeds and when they do, they pull up the landscape fabric with it. This results in an ugly flower bed with lots of exposed weed mat surfaces. If you do not regularly re-cover these exposed areas the sun begins to break them down. Eventually its one big mess. The only way to avoid this is to completely remove and replace the mulch every year to ensure no soil ever builds up on the mat surface.

In summary, weed mats have been a great seller for many companies and hundreds of thousands of home owners have bought into the marketing of these products. But they are more hassle and expense then they are worth. You are better off with a heavy layer of good hard wood mulch then adding a plastic product into your landscape.

Finally, if you are bringing in soil you need to determine what it is used for, if it is for a major flower bed with lots of perennials you may need to treat it differently than you would for a bunch or typical landscape shrubs. You can order fill dirt, top soil, screened top soil, pond muck, mushroom compost, planting mix, sand etc.  There are many options. But if you are doing a serious flower bed I would order a pre-mixed planting mix that is already suitable for your area and your purpose. It should have about 30% sand (not beach sand), 30% organic compost, and 30% native soil with 10% other improvements like expanded shale (tiny volcanic rocks), fertilizer, and micro nutrients.

I would call your local earth product distributors and ask what is available rather than trying to mix up your own mix.

You should till this in with you native soil so that you have 9-18" of loose loamy well drained soil and you will have great results.

Also, I just remembered from your posting that you are in Houston so you may not need as much sand in the mix as your existing soil may already be fairly sandy.
Good Luck


Sean J Murphy, LA,ISA, LEED AP
Please check out my blogs and articles on landscape topics like this on my websites.
http://www.seanjmurphy.com
http://amenityarchitects.com