How to Aerate Lawn Soil: Passes, Core Depth and 9 Machines’ Specs

Learning how to aerate lawn soil properly comes down to one number most guides leave out: holes per square foot. Purdue Extension AY-8 says aeration is most beneficial when cores go 2 to 3 inches deep and 20 to 40 holes are punched per square foot, and that most machines at rental agencies need multiple passes to get there. Spike tools that remove no soil do not count as aeration in that publication at all.

So we took the hole pattern printed in 9 aerator spec sheets and manuals (Billy Goat, Ryan, Classen and Bluebird) and did the arithmetic. One pass of a walk-behind drum aerator, the kind rental stores stock, leaves 4.3 to 6.2 holes per square foot. That means 4 or 5 passes, not the 2 most guides describe, to reach Purdue’s floor. The makers’ own “holes per sq ft” figures run 7 to 64 percent above what their printed patterns produce, so we use the pattern number throughout.

How many passes does your aerator need?

Divide 144 square inches by the hole pattern to get holes per square foot from one pass, then divide 20 by that. A 4 x 7 inch pattern gives 144 / 28 = 5.1 holes, so 4 passes. Penn State Extension runs the same arithmetic for the common 4 x 8 inch pattern: 4.5 holes, which opens only 1.38 percent of the surface with 3/4 inch tines.

Machine	Type	Width and tines	Tine	Core depth	Hole pattern	Holes per sq ft, 1 pass (pattern math)	Maker’s stated holes per sq ft	Passes to reach 20 per sq ft	Minutes per 1,000 sq ft per pass at rated maximum	Weight
Billy Goat AE401H (AE400 ser)	Drum, walk-behind	19 in, 24 tines	5/8 in	Up to 2.75 in	4.75 x 7 in	4.3	Not stated	5 (21.7 holes)	3.2 min	242 lb dry
Billy Goat PLUGR PL1801H	Reciprocating, walk-behind	18 in, 4 tines	5/8 in	Up to 2.75 in	3.63 x 6 in	6.6	Not stated	3 (19.8 holes)	2.7 min	236 lb
Ryan Lawnaire IV with EST	Drum, walk-behind	19 in, 30 tines	3/4 in	Up to 2.75 in	3.75 x 7 in	5.5	9	4 (21.9 holes)	2.1 min	240 lb dry, 279 lb with weights
Ryan Lawnaire 28	Reciprocating, walk-behind	28 in, 8 tines	3/4 in	Up to 2.5 in	3.5 x 5 in	8.2	12	3 (24.7 holes)	2.5 min	404 lb
Classen TA22H	Split drum, walk-behind	21 in, 36 tines	3/4 in	Up to 3 in	3.4 x 7 in	6.1	6.5	4 (24.2 holes)	1.9 min	214 lb dry (sheet also lists 270 lb)
Classen PRO TA25DA PowerSteer	Split drum, walk-behind	24.4 in, 36 tines	3/4 in	Up to 2.75 in	4 x 7 in	5.1	6.5	4 (20.6 holes)	1.8 min	320 lb dry
Bluebird H424	Drum, walk-behind	17.5 in, 24 tines	3/4 in	Up to 3 in	4.5 x 6.5 in	4.9	6.7	4 (19.7 holes)	2.6 min	265 lb
Bluebird H530A	Drum, walk-behind	19 in, 30 tines	3/4 in	Up to 3 in	3.8 x 6.5 in	5.8	7.7	4 (23.3 holes)	2.4 min	288 lb
Bluebird H742	Drum, walk-behind	25.5 in, 42 tines	3/4 in	Up to 3 in	3.6 x 6.5 in	6.2	8.1	4 (24.6 holes)	1.5 min	420 lb

1. Ryan Lawnaire IV5.50
2. Ryan Lawnaire 288.20
3. Classen TA22H6.10
4. Classen TA25DA5.10
5. Bluebird 4244.90
6. Bluebird 5305.80
7. Bluebird 7426.20

Source: Ryan, Classen and Bluebird spec sheets and manuals Purdue AY-8 target: 20 to 40 holes per sq ft. The machine table above holds the same numbers and links each document.

Show the numbers

	From hole pattern (144 / pattern area)	Maker's stated holes per sq ft
Ryan Lawnaire IV	5.50	9
Ryan Lawnaire 28	8.20	12
Classen TA22H	6.10	6.50
Classen TA25DA	5.10	6.50
Bluebird 424	4.90	6.70
Bluebird 530	5.80	7.70
Bluebird 742	6.20	8.10

Two machines stand apart. The Ryan Lawnaire 28, a reciprocating unit, punches 8.2 holes per square foot by its 3.5 x 5 inch pattern, so 3 passes reach 24.7 holes. The Billy Goat white paper says its cam-driven AE1300H can place 8 to 48 holes per square foot in one pass when the operator slows down. Purdue agrees that aerifiers with reciprocating arms are the most effective type.

Tow-behind plug aerators sit at the other end. The Agri-Fab 45-0299 is a 48-inch tow-behind unit with knife-style plugger points; it weighs 94 lb, its tray takes up to 140 lb of added weight, but publishes no hole pattern. Purdue says aerifiers that roll behind garden tractors are less effective because they do not penetrate deep enough or punch enough holes.

Number of passes over the same area (passes)Measured asHoles from the machine's printed hole patternAeratorBilly Goat AE401H (4.75 x 7 in pattern)Billy Goat PL1801H (3.63 x 6 in pattern)Ryan Lawnaire IV (3.75 x 7 in pattern)Ryan Lawnaire 28 (3.5 x 5 in pattern)Classen TA22H (3.4 x 7 in pattern)Classen TA25DA (4 x 7 in pattern)Bluebird 424 (4.5 x 6.5 in pattern)Bluebird 530 (3.8 x 6.5 in pattern)Bluebird 742 (3.6 x 6.5 in pattern)

Holes per square foot

8.7

Percent of Purdue's 20-hole minimum

43

Cores per 1,000 sq ft

8,662

Default: 2 passes with a Billy Goat AE401H = 8.7 holes per sq ft, 43 percent of Purdue's 20-hole minimum. Purdue AY-8 recommends 20 to 40 holes per sq ft; K-State's 3 inch spacing equals 16.

Core, spike, manual or liquid: which method actually aerates?

Only methods that pull a soil core relieve compaction on clay and silt. Nebraska Extension says solid-tine and spike tools, including aeration shoes, push soil particles apart and increase compaction between the holes, and that there is no chemical substitute for core aeration. Iowa State tells homeowners to avoid spike devices.

Method	Depth	Holes per sq ft per pass	Speed	Removes soil?	Source
Walk-behind drum core aerator (rental)	Up to 2.75 to 3 in	4.3 to 6.2 by pattern	19,000 to 40,000 sq ft/hr rated	Yes	Maker sheets in table above
Reciprocating (cam) core aerator	Up to 2.5 to 2.75 in	6.6 to 8.2 fixed; 8 to 48 variable (AE1300H)	22,000 to 24,000 sq ft/hr rated	Yes	Billy Goat PL1800; Ryan Lawnaire 28; Billy Goat
Tow-behind plug aerator	Up to 3 in (Agri-Fab)	Not published	Tractor speed	Yes, shallower	Agri-Fab; Purdue AY-8
Hand coring tool (2 tubes)	About 3 in	2 per plunge: 10 plunges per sq ft for 20 holes	Spot work only	Yes	Clemson HGIC 1200; our arithmetic
Spading fork, rocked	At least 4 in	Depends on tine count	Spot work only	No; compacts around the hole	Clemson HGIC 1200
Spike aerator or aeration shoes	Short spikes	Varies	Fast	No; adds compaction between holes	Nebraska; K-State MF2130
Liquid aeration spray	None	None	Spray	No	Colorado State 1545; Henry et al. 2025

Liquid aeration has one field trial behind it, and it lost. In a 2020 to 2022 Georgia study on TifTuf bermudagrass over Cecil clay loam, Henry and colleagues found only sequential hollow-tine cultivation reduced penetration resistance and raised long-term water infiltration, and concluded that liquid aeration does not substitute for it. Price comparisons for both services are in our lawn aeration cost guide.

Hand tools fit a dog run, not a yard. At 2 cores per plunge, 20 holes per square foot means 10 plunges per square foot, or 10,000 for 1,000 square feet. Clemson recommends a sod-coring tool over a spading fork for small areas because the fork forces soil closer together around each hole.

What do you do the day before aerating?

Test the soil, water if it fails, mow to your normal height and mark everything the tines could hit. The order matters because watering after flagging can knock flags over, and dry clay can break tines: Penn State warns that tines in dry soil will not go deep enough and risk breaking, while wet soil adds compaction.

1. Probe the soil. Push a garden spade or large screwdriver into the lawn. The Bluebird aerator manual says it should drive in 2 to 3 inches with little effort; if it will not, water the lawn the day before.
2. Water by the day, not by the inch. Colorado State, Billy Goat and Ryan all say to water thoroughly the day before; Nebraska Extension says to water deeply 2 days ahead in dry weather. Agri-Fab’s manual says 1 to 2 hours of sprinkling for extremely hard, dry ground. None of the extension publications or manuals we read sets an amount in inches.
3. Check it is not too wet. If soil sticks to your shoes or to a soil probe, wait for it to dry (Clemson HGIC 1200). Wet soil clogs tines and they stop dropping cores (K-State MF2130).
4. Mow at your normal height. The Billy Goat AE401 manual says to mow to the lawn’s normal cut height; the Agri-Fab manual adds to remove loose clippings first. Neither tells you to scalp.
5. Flag what is buried shallow. Mark sprinkler heads, shallow irrigation lines and cable TV lines (Colorado State 1505), plus valves, stakes and clothesline anchors (Bluebird manual).
6. Request an 811 locate. The 811 service is free and asks for a few business days. Michigan’s MISS DIG 811 says notice is required at least 3 business days ahead for any project regardless of size or depth, and that private lines, such as irrigation or landscape lighting, will not be marked.

1. 1Is the grass dormant, the ground frozen, or is it extremely hot and dry?

   YesWait. Aerate when the grass is actively growing (Nebraska Extension; Colorado State). See when to aerate your lawn.

   NoGo to the next question

2. 2Does soil stick to your shoes or to a probe?

   YesToo wet: wait for it to dry (Clemson HGIC 1200).

   NoGo to the next question

3. 3Will a screwdriver or spade fail to go in 2 to 3 inches with little effort?

   YesWater thoroughly today and aerate tomorrow (Bluebird manual; Colorado State).

   NoGo to the next question

4. 4Are sprinkler heads, shallow lines or cable runs unflagged?

   YesFlag them, and request an 811 locate a few business days ahead (Colorado State; 811).

   NoGo to the next question

5. 5Is the thatch layer more than 1 inch thick?

   YesDethatch first; aeration alone reduces thatch only over several years (Purdue AY-8).

   NoAerate: mow at normal height, add weight, run crossing passes until you reach about 20 holes per square foot, and measure a few cores for 2.5 to 3 inches.

Source: Clemson HGIC 1200; Colorado State 1505; Bluebird manual; Nebraska Extension; Purdue AY-8

How do you run the aerator?

Run straight, overlapping rows the way you mow, then cross them. Clemson HGIC 1200 says to go over the lawn twice, the second time perpendicular to the first, and K-State’s Johnson County office says at least two directions, with holes about 3 inches apart, gives the greatest benefit. Most drum machines need 4 or 5 passes to reach 20 holes, so plan at least 2 crossing pairs on compacted areas.

1. Add weight. Fill the water drum (5.2 gal on the Lawnaire IV) or mount the weights: 2 x 36 lb on Bluebird drums, a 42 lb bar plus a 9.5 gal drum on the Classen TA25DA.
2. Engage tines only on turf. Ryan and Bluebird both say never cross sidewalks, driveways or stepping stones with the tines down.
3. Lean on the handle. Billy Goat and Ryan say downward pressure on the handle gives maximum tine penetration. Start at about half throttle (Billy Goat AE401 manual).
4. Lift to turn. At the end of each row, release the clutch, raise the tines and pivot; Ryan pivots the Lawnaire IV on its water drum.
5. Measure the cores. Pull 3 or 4 and check length: Penn State wants a full 2.5 to 4 inch core, Nebraska at least 3 inches. Short cores mean dry soil or too little weight.
6. Add passes where it is hard. Hit paths, gates and dog runs again rather than the whole lawn (Nebraska lists them as the first places compaction shows).

Slopes: which way to run

The manuals disagree on direction, so follow the one for your machine. Bluebird and Agri-Fab say up and down; Ryan says across for walk-behinds; Billy Goat splits it at 45 degrees.

Machine	Direction on slopes	Stated limit	Source
Bluebird 424, 530, 742	Up and down; move the removable weight to the uphill side if you must cross	35% grade maximum	Bluebird manual
Billy Goat AE401	At a 45 degree angle to the slope, not straight across	20 degrees	Billy Goat AE401 manual
Ryan Lawnaire IV and V	Across slopes with walk-behind machines, not up and down	Too steep if the machine must be crabbed or turns downhill	Ryan manual
Agri-Fab 45-0299 (towed)	Up and down, never across the face	Stay off steep slopes	Agri-Fab manual

What do you do with the cores and the lawn afterward?

Leave the cores, water the lawn and decide on seed. Colorado State says to leave cores on lawns with more than 1/2 inch of thatch so they work back in, and to water soon after aerating. Iowa State suggests pulling a drag mat or a weighted piece of fencing to break them up; its FAQ says mowing over them breaks them up too.

Rake the cores instead if you mow with a reel mower: the Agri-Fab manual warns that small rocks and gravel in the plugs can damage blades. A 4,000 sq ft lawn aerated to 20 holes per square foot gives 80,000 cores, up to about 2 cubic yards of soil at 3/4 inch by 2.75 inches each, which is why raking them all is rarely worth it.

Seed and fertilizer can go down right away by Colorado State’s rule; Iowa State prefers fertilizing 1 week before. Clemson recommends 6 to 10 passes when seeding and waiting about a month before sowing so seed does not sprout only in the holes; rates and timing are in our guide to overseeding a lawn. Make crabgrass preventer applications after aerating (Clemson), though Nebraska turf research found aerating after a preemergence herbicide did not reduce control.

If the probe test showed the hard layer goes deeper than 3 inches, tines will not reach it: K-State puts construction-equipment compaction at 6 inches. Our guide to planting grass seed on hard dirt covers tilling for that depth, and the right month for your grass is in when to aerate your lawn. Thatch over 1 inch is a job for dethatching first.