How to manage a tall fescue lawn

Having a healthy lawn depends on just a few things: proper seed, soil, water, nutrients, and temperature.

Rule number 1 of grassland ecology. If you want to understand the grass, look at its roots.
Diagram of prairie grasses showing growth above ground and below ground.

Yesterday, on a particularly balmy day in February, I manhandled a Ryan Pro Core Aeration machine (see Methods section) around my yard in Greenville, SC. This poked holes about 1.2 inches deep and 4 inches apart throughout my yard. This activity littered my yard with dirt plugs — our “scientific” samples.

Soil plugs generated by core aeration.

Inspection of the plugs revealed sparse root growth below the top quarter inch of soil.

Inspection of plugs. Left: raw plug. Right: plug with soil gently removed to reveal roots.

What to do?

Our options for improving root growth are:

  • Water more or less
  • Over seed with new/better seed
  • Mount a defense — apply pre-emergent weed killer
  • Improve the soil

Let’s think about our options.

Water less. When we purchased our house (about 8 months ago) the irrigation system was set to water for 12 minutes, daily. Frequent watering promotes shallow root growth. I have already switched to an every-other-day watering cycle. Evidently, even this is too often. This article by Super Sod (sod manufacturer) recommends watering with no more than 1 inch of water per week. This translates into watering once a week, at most.

Over seed. I could over seed with grass that is more adept at establishing stronger roots. Tall fescue has a very wide range. Fescue that thrives in the Dakotas probably won’t do as well in Carolinas. Seed is tuned for climate zones. We might be able to do better with different seed. I’ll keep this in mind.

Apply pre-emergent weed killer. This is certainly an option, but this is really a band aid to prevent weeds from taking over areas where the turf is thin. This is a defensive action.

Improve the soil. This seems like the best — and most sustainable — solution. Yes, let’s mount a good offense!

Plan: improve the soil

Geography

Greenville is in the northern piedmont, the foothills of the blue ridge mountains. Greenville county extends up the southern escarpment of the Blue Ridge. So, once you drive up, up, up the mountain you get to North Caolina.

The piedmont plateau is famous for its “red clay”. The distinctive red color is from a long-term weathering processes that leaves behind iron oxides. The red clay’s mixture of silicon, aluminum, and other elements, including iron oxides, is called saprolite, which erodes easily when trees and other vegetation are removed. The more rugged topography of the northern Piedmont results in a thinner soil, while a more nutrient-rich soil, better suited for growing crops, occurs in the region’s southern portion.

Piedmont soil is is mostly mixture of sand, clay and granite. Granite is usually concentrated in mountains — so-called blue ridge outliers — that dot the otherwise flat landscape of the piedmont. Examples: King’s Mountain, NC; Paris Mountain, SC; Stone Mountain, GA. Clay and sand are both sediment — clay consisting of finer grains (more weathered) than sand.

So, the soil in the upper piedmont (my back yard) is a mixture of sand and clay. This is a far cry, in terms of fertility, from the beautiful black loamy soils in the midwest, and the black belt —the crescent-shaped region about 300 miles (480 km) long and up to 25 miles (40 km) wide, extending from southwest Tennessee to east-central Mississippi. Incidentally, black within “black belt” refers to the color of the soil, not the the skin color of the slave labor that toiled in the cotton plantations.

The question I will be answering is how to grow grass in sand and clay. We will be growing tall fescue, which is a cool season grass.

The difference between cool vs. warm season grasses will be covered separately.

Improve the soil

pH. pH is a measure of the acidity/alkalinity of the soil. piedmont clay is acidic (low pH). We need to raise the pH using crushed limestone.

Limestone

The “active ingredient” in limestone is calcium carbonate (CaCO3). Chemistry lesson: CaCO3 is a salt of Ca2+ calcium (divalent cation) and CO3 — (carbonate, a divalent anion). Carbonate is not happy about being so negative (-2 charge), so will bind pick up a free proton (H+) to become HCO3- (monobasic carbonate). So, carbonate picks up a proton, which raises the pH (recall, pH = -log(H+)). Adding limestone raises the pH. Hooray!

Crushed limestone, called pelletized lime, is sold in 40 lb bags at home centers.

Pelletized Lime: crushed limestone.

Whence limestone? During the Cretaceous period, about 145 to 66 million years ago, most of what are now the central plains and the southeast of the United States were covered by shallow seas. Tiny marine plankton grew in those seas, and their carbonate skeletons accumulated into massive chalk formations. Chalk can remain as chalk, disintegrate into black loam, or, with the addition of heat and pressure, become slate or limestone.

So, we’re adding limestone to our soil because the tiny marine plankton some 100 million years ago managed to die in the wrong place.

Fertilize

More Data:

  • In March, 2017 there were grass clumps where our dog had relieved herself that were about twice as tall as the surrounding grass.
  • We have clover. [Clover grows in Nitrogen-poor soils]

Conclusion: Not enough Nitrogen.

Action: Hammer the lawn with a balanced fertilizer, watering the lawn immediately afterward. This produced great results. We had a very lush green lawn for 3 months. I dealt with clover by spot spraying with 2,4-D.

Now what?

It is now late June, 2017. We had a lush lawn in the Spring, but I am seeing summer dye back. The grass grew up but it didn’t spread laterally, despite adding a high phosphorous fertilizer last fall to encourage root growth. Fescue grows in clumps. We need more clumps.

My plan is to over seed in the Fall (October). My concern is that over seeded grass will not last beyond the Fall and next Spring (i.e., dye back next summer). I need to solve this in order to see sustainable results.

Methods

Ryan “Pro” Core Aerator.