“Fall” Into Your Cool-season lawn: Soil Preparation Before Planting

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No matter the quality of the cool-season turfgrass you have selected for your site, it is absolutely essential that you provide it with soil conditions that promote both establishment and long-term performance.  This podcast details the steps in enhancing and improving soil conditions prior to cool-season turfgrass establishment.

No matter the quality of the cool-season turfgrass you have selected for your site, it is absolutely essential that you provide it with soil conditions that promote both establishment and long-term performance.  This podcast details the steps in enhancing and improving soil conditions prior to cool-season turfgrass establishment.

What kind of soil are you dealing with?
A constant problem in new construction is that many new home sites have had the topsoil removed and the homeowner is now left with a heavy clay subsoil in which to attempt to establish a lawn and landscape.  Of course, the most important step in this process if you have any control in the situation is to ensure that your topsoil is stockpiled (or replaced) and distributed uniformly over the property at a 4 inch depth before grassing.  More times than not, this is not the case and lots of seed and sod is planted on clay-based subsoil with only a very limited chance for success.  These temporary masking jobs look fine immediately after establishment (and during ideal growing conditions), but the turf usually struggles and often dies during the first environmental stress period it encounters.  Make sure in your new construction sites that you have ample topsoil for the lawn and landscape.  At the very least, if you are faced with managing a clayey subsoil, then follow the recommendations of your soil test to improve nutrient and pH levels, and consider adding 1-2 inches of a quality compost to the site and tilling it in to the top 3-4 inches of the existing soil.  Unfortunately, this is not a cheap alternative, and the need to do so can be voided IF you retained your topsoil.  In an era of environmental awareness, one of the most logical means of protecting our environment is to ensure a desirable soil that optimizes plant growth and development is in place.  Such a soil requires minimal chemical and physical inputs for successful turf and ornamental plantings.  It is commonly thought that the “answer” to undesirable soils is to simply add more fertilizer and chemicals to the system.  This rarely works, however, and the turf slowly declines in quality and density, thus leading to greater potential for nutrient and chemical pollution.    So work hard to ensure you have an acceptable topsoil to initiate your planting on new construction sites.  Don’t overlook this very important part of the construction process – accepting subsoil now in all likelihood means you will be dealing with constantly struggling or dying plants for years to come.

The Importance of Soil Testing.
Your grass seedlings or newly emerged roots from sod have an immediate need for plant-available nutrients.  For new plantings, it is logical that a soil test is a critical first step towards success.  However, the same logic applies for partial renovations or spot repairs as well -- a soil test is a must if you have not made one within the past 3 years.  How do you conduct a soil test?  Divide your lawn into sections (front, back, and side yards) and sample to a 4 to 6 inch depth in a zig-zag fashion around your lawn.  Take 10-15 samples per site and mix the samples together before removing a composite sample to submit for testing to a soil testing lab.  There are many private labs that offer soil testing services through lawn and garden centers or you can use your local VCE office to assist you with submitting the sample to the lab at Virginia Tech.  Within a week or so you will receive a test report detailing recommendations that particularly apply to your soil’s needs for lime, phosphorus (P), and potassium (K).  For new plantings, it is advantageous to incorporate the required chemicals into your soil before planting, whereas you will simply be applying the nutrients to the soil surface for your spot renovations.  

What about pre-plant fertilization? 
Depending on what your soil test report says, you may or may not need any additional nutrients other than a small amount of nitrogen.  It is normal in fall establishments to apply ½ lb of N/1000 sq ft for either new establishments or renovations, but what about the other nutrients?  The standard for many years has been to use a 1:2:1 fertilizer (e.g. a 5-10-5) that emphasizes additional levels of phosphorus, a nutrient known to enhance root development.  However, recent work by Dr. Mark Carroll at the University of Maryland indicated that if soil P was already in the high range according to testing, additional P was of no benefit in the seeding establishment of tall fescue (unless the seed was planted during colder than desirable temperatures for planting).  The bottom line is this:  be judicious when using P-containing fertilizers.  Excessive P can be a potential environmental problem.

Soil preparation.
The next step in establishment success is to ensure soil to seed/sod contact.  The new seedlings or sod must quickly develop a root system in order to extract the needed moisture and nutrients.  As recommended earlier, thorough tillage of recommended nutrients and lime to a 4-inch soil depth is ideal for new plantings.  However, don’t perform so much tillage that you completely destroy your soil’s structure—some clods are just fine!  Till your soil, but don’t turn it into powder.  Your grass seed (and yes, even your sod) will do just fine with some clods in the tilled area. 

Next, put a final grade on your site that ensures water movement is away from your house, your driveway, your sidewalk, etc.  Surface drainage is the most effective way to channel water away from your house, so don’t miss this opportunity to direct where the water will go. 

For renovations, tillage might be deemed excessive just to repair small areas, but you still need to do some type of soil preparation to encourage turf establishment because applying seed to unprepared soil is nothing more than putting out expensive bird food!  For spot sod installations, it is recommended to completely till the problem sites and refrain from simply laying the sod on the existing dead grass— your sod will struggle with rooting through the mat of dead grass on the soil surface.  For spot renovations for seeding, the use of a power rake, a vertical mower, or a core aerator will optimize soil to seed contact.  Another tool I have seen used quite successfully in soil prep for spot seedings is the garden weeding device with rotating blades on the end of a long handle.  I have had more success with it for this purpose than for weeding my gardens!  And finally, don’t forget that you can also rent power seeders from many equipment rental stores.  Many of these machines will actually vertical mow and seed in a single pass.

Following these steps in soil preparation will further your chances of establishment success.  Be sure to check this website for other related podcasts and extension publications that provide tips on how to successfully establish cool-season turfgrasses.  Don’t forget that your local Virginia Cooperative Extension office is always there to serve as a wealth of information and expertise towards your efforts to improve your lawn.