How to Dethatch a Lawn: Measure First, Then Match Reel and Month

The check most guides skip comes after the plug: the reel. Clemson and NC State want blades 2 to 3 inches apart on centipedegrass, and UF/IFAS wants 3 inches on St. Augustinegrass. The standard reels on Sunbelt Rentals’ dethatcher spec sheet list 11/16 inch or 1 inch where a spacing is stated. NC State warns that 1-inch spacing “may severely damage” centipedegrass. So the order here is plug, tool, reel, month. Prices live in our dethatching cost guide.

Step 1: Cut a plug and measure the thatch

1. Cut a wedge with a knife or spade, 2 inches deep (Minnesota) to 3 inches deep (UC IPM). It must reach mineral soil (Arkansas FSA-6139).
2. Find the layer between the green stems and the soil. It looks stringy or felt-like (Oklahoma State HLA-6604) and light brown, like peat moss (K-State).
3. Press it, then read a ruler. UMass takes its 1/2 to 3/4 inch reading “when you compress it,” so an uncompressed plug can push you over the line.
4. Repeat in several spots. Oklahoma State says to lift several plugs however healthy the lawn looks; take one each from the front, the back and any shade.
5. Set each plug back and water it.

A bouncy walk is a clue, not a measurement. C-shaped white larvae in the wedge point to a different problem, covered in our lawn grubs guide. Tall fescue rarely gets this far: NC State says removal is “generally not necessary” on it, and UGA prints the same words.

Compressed depth	Who treats this as the line	What they say
1/3 inch	Oklahoma State	Cool-season limit: fescue, bluegrass, ryegrass
1/2 inch	UC IPM, Clemson HGIC 2360, Minnesota, Texas A&M E-139, Arkansas, Colorado State, NC State (bermudagrass, zoysiagrass, centipedegrass), UGA, Oklahoma State (warm-season)	Dethatch, or start managing it. The default trigger for home lawns
1/2 to 3/4 inch	UMass, Pacific Northwest handbook, NC State (St. Augustinegrass, 3/4)	Upper edge of acceptable; plan removal past it
1 inch	Penn State, UF/IFAS LH010 (St. Augustinegrass), Milorganite, Sunday	Penn State: past this, “turf problems will likely result.” Two brand how-to pages use it as the trigger

1. Oklahoma State, cool-season0.33
2. UC IPM0.50
3. Clemson0.50
4. Minnesota0.50
5. Texas A&M0.50
6. Arkansas0.50
7. NC State, bermudagrass0.50
8. UMass (upper end)0.75
9. PNW handbook (upper end)0.75
10. NC State, St. Augustinegrass0.75
11. Penn State1
12. UF/IFAS, St. Augustinegrass1
13. Milorganite (brand page)1

Source: Extension publications and one brand how-to page, compiled by The Green Industry Report UMass and the PNW handbook publish a 1/2 to 3/4 inch band; the upper end is plotted. The table above holds the same figures, and the CSV holds every source.

Show the numbers

	Thatch depth, inches
Oklahoma State, cool-season	0.33
UC IPM	0.50
Clemson	0.50
Minnesota	0.50
Texas A&M	0.50
Arkansas	0.50
NC State, bermudagrass	0.50
UMass (upper end)	0.75
PNW handbook (upper end)	0.75
NC State, St. Augustinegrass	0.75
Penn State	1
UF/IFAS, St. Augustinegrass	1
Milorganite (brand page)	1

A guide that says to wait for 1 inch sits at the loose end: 9 of the 13 land-grant services above act at 1/2 inch or less on most grasses. Use 1/2 inch unless your state’s service says otherwise. Waiting has a cost, since Penn State says preventive care alone will not control a layer of 1 inch or more.

1. 1Does the compressed plug read 1/2 inch or less?

   YesLeave the thatch. Core aerate if the soil is compacted (K-State) and cut a new plug next year.

   NoGo to the next question

2. 2Is the grass weak, drought stressed or not yet fully green?

   YesWait. Dethatch only when it is actively growing with 3 to 4 weeks to recover (Penn State, LSU).

   NoGo to the next question

3. 3Is the layer over 1 inch?

   YesPlan partial passes over 2 to 3 years (Oklahoma State), or strip it with a sod cutter and re-establish (Purdue).

   NoGo to the next question

4. 4Is the lawn or patch small?

   YesUse a thatching rake (UC IPM, Clemson).

   NoGo to the next question

5. 5Is it St. Augustinegrass or centipedegrass?

   YesUse 2 to 3 inch blade spacing, one direction (Clemson, NC State). If the rental reel is tighter, test a hidden strip or ask a lawn company.

   NoUse a vertical mower with blades 1 to 2 inches apart, start high, and make a second perpendicular pass only if thatch remains (Clemson, Penn State, UC IPM).

Source: Clemson HGIC 2360, Penn State, Purdue AY-8, Oklahoma State HLA-6604, K-State, LSU AgCenter, UC IPM, NC State

Step 2: Pick the tool from the depth

Compressed depth or job	Tool	The trade-off	Source
1/2 inch or less	No dethatcher. Core aerate if the soil is also compacted	Slow: 1 pass with 1/2-inch tines at 2-inch spacing removes about 10% of thatch	K-State; Colorado State
Small lawn or patch	Thatching rake with thick blades	Hand labor; no published square-foot limit, only “small”	UC IPM; Clemson
Over 1/2 to 1 inch, large lawn	Vertical mower with knives or fixed blades	Lawn looks ragged; reseeding may be needed	Purdue AY-8
Light debris only	Spring-tine or wire power rake	Arkansas: usually ineffective at removing a large amount of thatch	Arkansas; Penn State
Over 1 inch	Several partial passes over 2 to 3 years, or a sod cutter and a new lawn	Partial: years of work. Sod cutter: full re-establishment	Oklahoma State; PNW; Purdue
2 inches or more	Vertical mower plus a seeding plan	Most roots sit in the thatch, so removal severely thins turf	Penn State
Spring blade on a rotary mower	Skip it	“Quite destructive” (Minnesota); “may be hazardous” to you and the mower (PNW)	Minnesota; PNW; Purdue

“Power rake” is not one machine. NC State and Minnesota use it as another name for a vertical mower, Utah State means hinged blades, and Arkansas means flexible wires. Ask the rental counter what is on the reel, then see the next table. This matters most on the 1/2 to 1 inch band, where Purdue prefers blades over flexible tines.

Step 3: Match blade spacing, depth and passes to your grass

Grass	Blade spacing	Depth	Passes	Source
Kentucky bluegrass, red fescue	1 to 2 in (Clemson); 1 in (UGA)	Into the soil, per Clemson; Utah State and the PNW handbook stay above it	Several directions (Clemson); 2 (UGA)	Clemson; UGA; Utah State; PNW
Bermudagrass	1 to 2 in (Clemson); 1 in (UGA)	Through thatch into the soil surface (Texas A&M)	2 (UGA); 2 or 3 (Texas A&M)	Clemson; UGA; E-139
Zoysiagrass	1 to 2 in (Clemson); 1 in (UGA)	Light: NC State warns it recovers slowly, so split removal over seasons	Several (Clemson); 2 (UGA)	Clemson; UGA; NC State
St. Augustinegrass	3 in (UF/IFAS, NC State); 2 to 3 in (Clemson); 1 in (UGA)	Slightly into the soil (UF/IFAS)	1 (Clemson, UGA); never all 4 directions (UF/IFAS)	LH010; NC State; Clemson; UGA
Centipedegrass	2 to 3 in (NC State, Clemson); 1 in (UGA)	1/4 in (NC State)	1 (all three)	NC State; Clemson; UGA
Tall fescue, perennial ryegrass	Wider than creeping grasses, if at all	Higher than creeping grasses	Rarely needed	UC IPM

Depth is where publications split hardest. Clemson wants blades at least 1/2 inch into soil and UC IPM about 1 inch for creeping grasses, while Utah State says blades should not touch soil and the Pacific Northwest handbook starts 1/4 inch above a sidewalk. The two western sources write mainly for cool-season lawns. Our reading: begin at Penn State’s high setting, check one strip, then step down.

Machine	Standard reel	Listed reel option	Width	Source
Billy Goat PR550H	Flail; spacing not listed	Spring tine, Vertaslicing	20 in	Sunbelt
Classen TR-20H	Flail, 11/16 in	Adjustable up to 1 3/8 in	20 in	Sunbelt
Classen TRC-20H1	Flail, 11/16 in	Adjustable up to 1 3/8 in	20 in	Sunbelt
Ryan Ren-O-Thin IV	Flail, 1 in	Verticut, 3/4 to 2 in	18 in	Sunbelt
Ryan Ren-O-Thin (dealer listing)	Fixed, 1 in	Flail 1 in; spring 3/4 in. Depth: 1 in above ground to 7/8 in into it	18 in	Arco Lawn

Only the Ren-O-Thin’s optional verticut reel on that sheet reaches 2 inches, and none lists 3. That is fine for bluegrass or bermudagrass, where Clemson allows 1 to 2 inches. On St. Augustinegrass or centipedegrass, measure the reel with a tape before paying. If it is tighter than 2 inches, UGA’s calendars accept 1 inch in a single direction but NC State, Clemson and UF/IFAS do not, so the cautious choices are a hidden test strip at NC State’s 1/4-inch depth or asking a lawn company what spacing it runs.

Step 4: Choose the month: a dethatching calendar by grass

Swipe the table sideways to see every column.

Grass, state (source)	J	F	M	A	M	J	J	A	S	O	N	D
Kentucky bluegrass, Pa. (Penn State)								●	●
Kentucky bluegrass, Ind. and Ill. (Purdue)				●					●
Kentucky bluegrass, Kan. (K-State)									●
Cool-season, Minn. (Minnesota)								●	●	●
Cool-season, Okla. (Oklahoma State)									●	●
Cool-season, western Ore. (PNW)			●	●	●				●	●
Kentucky bluegrass, Ga. (UGA)	○	○	○	○						○	○	○
Bermudagrass, N.C. (NC State)					●	●	●	●
Bermudagrass, Ga. (UGA)					○	●	●	○
Bermudagrass and zoysiagrass, Okla. (Oklahoma State)		●	●
Zoysiagrass, N.C. (NC State)					●	●	●
Zoysiagrass, Ga. (UGA)					○	●	●	○
Zoysiagrass, Md. (Maryland)						●
St. Augustinegrass, Fla. (UF/IFAS)			●	●	●	●	●
St. Augustinegrass, Ga. (UGA)					○	○	○	○
Centipedegrass, N.C. (NC State)					●
Centipedegrass, Ga. (UGA)					○	○	○

Two patterns stand out. September appears in 6 of the 7 cool-season rows, and June in 8 of the 10 warm-season rows. LSU AgCenter gives the reason: the grass needs active growth and about 3 to 4 weeks to recover. For warm-season lawns, NC State says to vertical mow only after complete green-up, “or recovery will be very slow.”

Oklahoma State’s February and March window, before green-up, and Texas A&M’s “early spring” are the outliers. We side with the majority unless you live under those two services. Spring work on cool-season lawns also invites weeds, as Penn State notes, and UC IPM says to apply preemergence herbicide after dethatching, not before; label wait times are in our crabgrass guide. Core aeration windows are in our aeration timing guide.

The dethatching job, in order

1. Flag sprinkler heads and hidden objects (Milorganite gives this tip too).
2. Lightly moisten the soil surface (UC IPM). UMass says not to dethatch wet soil, and LSU says very dry soil stops the blades.
3. Mow a little lower than normal (UC IPM). NC State uses 2 1/2 inches on St. Augustinegrass.
4. Set depth on a sidewalk: the PNW handbook starts about 1/4 inch above the hard surface. Make a test strip somewhere hidden, as Penn State advises, and adjust.
5. Make one pass at a slow, steady pace (PNW) in one direction, using the settings in the table above.
6. Rake up the debris and look. Stop “when you start tearing chunks of turf out of the ground” (PNW).
7. On bluegrass, bermudagrass or zoysiagrass, make a second pass perpendicular to the first if thatch remains (UC IPM). Skip this on St. Augustinegrass and centipedegrass.
8. Remove all debris, mow to tidy the surface and irrigate immediately so exposed roots do not dry out (UF/IFAS). Compost the debris; Colorado State says composting kills living grass in it before it goes on beds as mulch.

Recovery: the first 4 weeks after dethatching

When	Do this	Rate or limit	Source
Same day	Water thoroughly so exposed roots do not dry	Immediately after cleanup	UF/IFAS; Clemson
Same day, after dethatching	Topdress, lime or seed: after the dethatcher, not before	Topdress 1/8 inch (UMass, Texas A&M) to 1/4 inch (UF/IFAS, UGA)	Oklahoma State; UMass
Same day or week, cool-season lawn	Overseed thin areas	May be needed once removal starts at 1/2 inch or more	Purdue; Penn State
1 week later	Feed and water in	St. Augustinegrass 1/2 lb N per 1,000 sq ft (UF/IFAS); 1 lb (Clemson). Minnesota uses 1/2 to 3/4 lb with no stated wait	LH010; Clemson; Minnesota
Weeks 1 to 4	Keep mowing and irrigating. No repeat dethatching	About 3 to 4 weeks to recover	LSU AgCenter
Next year	Cut a new plug before booking anything	Act only past your threshold	UC IPM

Use the lowest nitrogen figure if the lawn was fed in the past month, and check the calendar first: NC State says not to feed centipedegrass before mid-May, and Arkansas caps zoysiagrass and centipedegrass at 1 to 2 lb per year. The bag arithmetic is in our lawn fertilizer guide, and seed rates are in our overseeding guide. St. Augustinegrass “cannot be established from seed” (UGA), so its bare spots need sod or plugs.

What thatch is, what it is not, and which grasses build it

Thatch is mostly stems, crowns, rhizomes, stolons and roots, about 25 percent of it decay-resistant lignin (Penn State). Clippings are not the cause: they are 85 percent water (Texas A&M), and a 1967 University of Rhode Island study (Ledeboer and Skogley, Agronomy Journal 59:320) found leaves and clippings do not contribute. Arkansas FSA-6139 summarizes later work, including only a 3 percent rise in zoysiagrass thatching tendency when clippings stay.

One caveat: Oklahoma State says infrequent mowing can leave long clippings that cannot reach the soil, and Arkansas says heavy clipping loads can tie up decomposing microbes. Decisions on what to do with them are in our grass clippings guide.

Grass	Thatch tendency	How often it may need removal	Source
Zoysiagrass	High	Every 1 to 2 years (UF/IFAS); every 3 to 5 (NC State)	Arkansas; LH011; NC State
Bermudagrass	High; medium to high (LSU)	Yearly possible; monthly in summer at most if recovery allows (NC State)	Arkansas; LSU; UC IPM; NC State
Kentucky bluegrass	Medium (Arkansas); heavy (Clemson)	Yearly or every other year	Clemson; PNW
St. Augustinegrass	Medium; medium to high (LSU)	When a plug passes your threshold	Arkansas; LSU
Centipedegrass	Medium (Arkansas); low to medium (LSU)	Rarely thick in Oklahoma; use moderation	Arkansas; LSU; Oklahoma State
Creeping red fescue, creeping bentgrass	Thatch formers; bentgrass medium (Arkansas)	Bentgrass may need it yearly	Penn State; Arkansas; UC IPM
Tall fescue, perennial ryegrass	Low	Every few years at most	Arkansas; UC IPM
Buffalograss, bahiagrass	Rarely a problem	Rarely	Colorado State; UF/IFAS LH006

What drives buildup is nitrogen, water, pH and soil life. Texas A&M caps nitrogen at 1 lb per 1,000 sq ft per application, Penn State says soil at pH 5.5 or lower inhibits the decomposers (see soil testing and lime), and both Texas A&M and PNW say bacteria or enzyme products have not been shown to work.

Soil life may matter most. A bluegrass study in the 1973 Michigan Turfgrass Conference proceedings ran from 1962 and found no significant thatch difference in fall 1972 across two mowing heights, clippings returned or removed, annual dethatching or none, and 4 to 14 lb of nitrogen a year. An adjacent alley that received chlordane in 1963 and 1966 did have thatch, and the paper credited earthworms. That is one site and one observation, but it fits Penn State’s warning about insecticides.

This page is general information. Follow the label on any fertilizer or herbicide you apply after dethatching, and the operator manual and safety decals on any rented machine.