A garden lawn is probably the most hostile environment provided by gardeners in furtherance of obtaining a beautiful garden. This is one reason for aerating a lawn. Nowhere else are plants - and grasses are indeed plants - subjected to such willful abuse than on the garden lawn.
Our grasses were originally grown as food crops for grazing animals - sometimes natural as with the sea marshes for grazing geese, and sometimes agriculturally for grazing cattle. We will omit the grasses that are grown as cereals, for they are generally not of the varieties that we have adapted for lawn use.
No other range of garden plants suffer - or would tolerate - the abuse that we heap upon those that serve us as our lawn! In 'normal' use our lawn is trampled in all manner of operations. Mowing, games, even walking, all serve to gradually compact the top few inches of soil that is largely responsible for the continuing health of the lawn grasses.
This compaction of soil does two things that are detrimental to our lawns. Trampled - or compacted - soils gradually prevent the free movement of water to the roots zone, and also exclude the all important air from the soil.
A single 'core' taken from a Lawn Aerating machine. This shows a heavy soil, a build up of thatch starting, and very poor root growth. The heavy, poorly-drained soil is conducive to the coarse grass that is seen here.
Compaction in itself is reason enough to somehow aerate the soil under the lawn: another reason is that of 'thatch' which builds up as a layer of almost impenetrable 'straw' on the surface of the soil beneath the green grass that we see.
Whilst lawn thatch can be removed over time with raking the lawn, compaction needs more drastic action by aeration of the top 4 inches of soil beneath the lawn. Most of the operations that serve to aerate your lawn will also negate the effects of thatch build up.
Plant roots need air - or Oxygen to be more precise - to develop and grow. Whilst some plants are well adapted to growing in bogs, swamps etc, grasses are not. They need to be able to access Oxygen from the minute spaces between the individual root particles (crumbs). They cannot assimilate Oxygen from water - even though water is composed of Oxygen and Hydrogen. Soil compaction does two things that are detrimental to good root growth. Aerating a lawn dose much to redress the balance ...
Aerating a lawn is simply the means of getting air - and also water - freely available to the lawn grass plant roots. It can be done over time by 'opening up' the structure of the soil below the turf, which is a long term solution. But, it is normally achieved as a result of a noticed problem with waterlogged lawn areas or poor turf sod growth.
If aeration is needed, it is normally needed quickly, with no time for the preferred long term solution of building up organic matter in the soil.
Aeration of the lawn is normally carried out by either spiking the lawn with fork tines, or using a device with hollow tines. Over time, the addition of sharp sand to the surface of the lawn - and brushed in - can also lead to aeration, as the sand is taken down into the soil by various activities - thereby opening up the crumb structure.
The simplest method - for small isolated areas - of aerating a lawn is by 'spiking' with a sturdy, normal garden fork. A digging fork (rather than a border fork) is best for it has a wider 'tread' area. A pair of hefty boots will be a requirement if you are not to suffer sore foot instep problems. As with digging, you should place the heel of the foot onto the fork and not your instep!
The fork is simply forced into the lawn to a depth of 3 - 4 inches, and gently rocked back and forth to both enlarge the holes slightly and to facilitate the removal of the fork from the soil. Best done of course when the soil is moist - even if you water it the previous evening! If you are up to it, large areas can be done this way.
After your first set of holes (4) just move backwards around 6 inches and repeat. There is no science as to how close your sets of holes should be. Anywhere between 6 in - 9in is fine. In tandem with this operation - especially with heavier soils of areas that are prone to compaction - (natural path lines, under the washing line, under overhanging trees etc) it would be a good idea to apply a suitable top dressing, brushed into the holes.
This will provide natural water/air channels for many a year! It will certainly aid surface drainage, though might need additional work if there is a substantial drainage problem - rather than simply compaction.
Another variation on the common garden fork spiking, would be the hand propelled (pushed) spiked roller. This is better if weights can be added to allow for better penetration of the soil - otherwise it will simply roll along the lawn, leaving nothing more than a few dimples. It will not provide the hollowed out aeration holes, such as are seen in the image
If you want to go one better with the manual treading operation, you can purchase or rent a hollow tine fork. This will be harder work, as you will then be taking a full core of soil out of the ground - as in the image above. However, you will have a series holes, which can either be left 'open' or better still - top dressed with a good open mixture top-dressing. The image above shows course sand ready to be brushed into the hollow tine holes. It is good idea to do this as you progress - brushing into the holes before you have to trample over them again!
This is hard work! The shoes are normally slip-over plastic/rubber pads with a number of spikes. The spikes are not much more than threaded nails, held into place with screw fastening. because they are thin, you will not expect the type of hole you will get with a lawn spiked roller, and certainly not a core of soil removed. They are not hollow tines.
Providing the lawn is moist, and the soil reasonably soft, then it is possible to get a few holes in the lawn, which can then have sand brushed into them. Many 'purists' say that lawn spiking shoes do not work, and it would be folly to think that you can spike a whole lawn - even a small one - without feeling the effects in your muscles.
But, with a well-watered lawn, it is possible to do more good than harm by treading with lawn aeration shoes. The best way forward is to walk-spike the lawn on a moist surface, then let it dry out and brush sand into the resultant holes. Even a penetration of a couple of inches helps with surface water drainage. If you are up to it physically - and like to have something to boast about - then lawn aerator shoes will work for you!
Make sure that you slip the aerator shoe over a sturdy boot or shoe. Do NOT be tempted to simply slip them over your feet - however man you think you are!
The top-end, ultimate lawn aeration equipment is the 'ride-on' professional job as seen being used on this golf course green. It is only of use for large lawn areas, where you do not constantly have to do tight turns on the grass - which will only lead to further compaction. This type of machine invariably has (Should have) wide tread tyres which spreads the weight load - avoiding severe compaction.
Smaller versions of this machine are available from professional sources or from good hire shops.
Walk-behind machines - similar to motorised lawn-mowers are also available and probably more suited to amateur or occasional use. This type of aerator will also do a good job - removing complete cores of earth from the lawn - normally leaving a hole around 2-4in depth. With the walk-behind machine, it is better if you can walk to the side of the machine and not therefore crush the resultant soil cores on the surface.
The cores can either be brushed back into the surface of the lawn - breaking up as they enter the holes from which they came. This then replaces the soil back into the lawn, but leaves the un-compacted holes in place. This is best done if there is a light soil. heavier soils such as clay and silt soils would be better served if the cores were brushed off and a suitable open textured top dressing applied as mentioned earlier.
Lawns should be aerated not more than annually - unless there is a very severe case of compaction. This would be the exception rather than the rule. It may well be that your lawn does not ever need to be aerated.
The standard non-professional test to see if your lawn needs aerating, is simply to push a screwdriver down into the lawn when the soil is moist. If it can be pushed in a few inches, then the likelihood is that your lawn will not need aeration. BUT, a contradiction to this rule/test is if you have a clay soil. This will enable the screwdriver to be inserted into the soil far easier than a sandy soil -and certainly if your soil is stony.
A visual test and experience of what your lawn surface should be like after heavy rain is probably a better guide. I would argue that a sandy soil will rarely ever need aerating, and then only if organic matter were to be incorporated by way of top dressing. Otherwise, the lawn will dry out even quicker as a result of aeration. Not a good idea on well drained drought susceptible light soils.
Soil core aeration is often recommended as being suitable for thatch removal. Not so, thatch removal would always be better carried out by raking - manually or mechanically.
Autumn or Spring would be ideal times to carry out lawn soil aeration. Spring, when the soil is moist and the rapid growing grass will soon cover up any unsightly mess left my core removal is better. Problem being, that there are so many other jobs that need doing at that time.
Any lawn fertilising or feeding should be carried out prior to soil aeration. This will ensure that there are no localised build-ups of scorching fertiliser brushed into the core holes.
If aerating a lawn is carried out in the fall, it is best done several weeks before the normal slow-down of grass growth - again to allow the lawn to recover and regain its cosmetic appeal before the winter sets in.
One of the best examples I have seen of how beneficial the addition and brushing in of sand is to a potentially compacted area, was on a football pitch in Surrey - on heavy near clay soil. The goal mouth at one end, and the opposite half of the centre circle were treated monthly with a dressing of sharp sand - simply brushed into the sward. At the end of the football season, both sanded areas were far superior in terms of grass cover than the un-sanded areas.
So - whilst not strictly lawn aeration - this could well be the answer to many localised areas on domestic lawns as a medium and long term measure.