Turf-type tall fescue: deep roots, no rhizomes, high cut

Tall fescue is the drought answer for the transition zone and the wrong choice for anyone who wants a low, tight lawn. It roots to 250 mm, tolerates 40 mm of mowing without complaint, and cannot fill a bare patch by itself. The whole profile follows from a mow range of 50 to 70 mm and 12 g of nitrogen per square metre per year.

Why the cut has to stay high

Turf-type tall fescue carries its growing point above the soil surface and has no rhizomes to rebuild from. Set the reel or rotary deck to 50 to 70 mm as the permanent band. Below 40 mm you are cutting into the crown on a regular basis and the stand thins from the middle outwards, one plant at a time, with no way back except seed.

The coarse leaf blade is why this looks like a pasture lawn at 70 mm and like a proper lawn at 50 mm. If the look matters more than the water saving, run it at 50 mm and accept a weekly cut in spring. If water matters more, run it at 70 mm and cut every 10 to 14 days.

Root depth and irrigation arithmetic

Roots reach 150 to 250 mm in a loam, which is 50 to 100 mm deeper than Kentucky bluegrass in the same soil. Drought tier is 4 out of 5. In practice a tall fescue lawn in the transition zone survives on 20 mm of water per week where a bluegrass lawn of the same area needs 30 mm.

Water to the root depth, not to a schedule. Apply 20 mm in one shot so the moisture front reaches 150 mm, then wait until the soil at 100 mm is dry to the touch before repeating. Two 10 mm sips two days apart wet only the top 50 mm and grow a shallow, heat-sensitive root system.

Nitrogen at 12 g per square metre, split 45:20:35

Tall fescue is a light feeder compared with bluegrass. Budget 12 g of nitrogen per square metre per year and put the weight on the two ends of the season: 45 percent in the late-spring window, 20 percent in early summer, 35 percent in early autumn. On 100 square metres that is 540 g, 240 g and 420 g of actual nitrogen.

The 20 percent summer slice exists only to carry the lawn through the heat. Exceed it and you push leaf growth at the exact moment the roots are shutting down, which is how summer patch and brown patch get a foothold.

Renovation, because it cannot repair itself

Recuperative rating is 2 out of 5. A bare patch stays bare until seed goes into it. Overseed at 30 g per square metre in early autumn, slit-seeding into the existing stand at 20 mm spacing so the seed lands in mineral soil rather than on top of thatch. A 70:30 tall fescue and Kentucky bluegrass blend gives you the fescue drought tolerance plus bluegrass rhizomes to fill small voids.

Do not overseed tall fescue in spring. Soil temperature above 15 degrees Celsius plus a 10 to 14 week establishment window puts the seedlings straight into summer heat with a 50 mm root system, and losses of 60 percent are normal.

Questions that come up on this page

Can tall fescue be cut at 35 mm?

Not for a full season. It survives a few cuts at 35 mm, but the crown sits high, and repeated cutting at that height removes it. The floor for this species is 40 mm and the working band starts at 50 mm.

Why does tall fescue form clumps?

Because it has no rhizomes. Each seed becomes an isolated bunch. Clumping is the visual signature of a thin stand, and the fix is slit-seeding at 30 g per square metre in autumn, not fertiliser.

Is tall fescue shade tolerant?

Rated 4 out of 5, the best of the cool-season bunch grasses, but shade tolerance only holds if you also raise the cut to the top of the 50 to 70 mm band and cut nitrogen by a third.

Sources

The public reference material the figures on this page were checked against:

• Illinois Extension
• Purdue Extension
• New Mexico State University
• Wisconsin Extension Bulletin A3710