Landscaper Pro Advice: Aeration and Scarification
Aeration is an important operation for all turf areas although the regularity and intensity with which an area needs to be treated will vary according to a number of factors. Most importantly is the level of wear an area is subject to together with its underlying soil type. A heavily used area with a fine, clay-dominant soil will be more prone to compaction and will therefore require a more intensive and regular aeration regime compared with an area subject to little wear and having a light, free-draining, sandy soil.
Why do I need to aerate?
Healthy soils are made up of a mixture of solid soil particles, water and air together with micro-organisms and organic matter. We use aeration to keep a soil healthy, to maintain the balance of air and water in the soil. A well aerated soil will absorb rainfall and irrigation water effectively. It will drain well and stay aerated. This is important because most beneficial micro-organisms are aerobic in nature and as such require oxygen to metabolise. In poorly aerated soils the micro-organisms cannot function normally. As a consequence, organic matter cannot be broken down effectively reducing the recycling of vital nutrients.
Additionally, all plants must develop an extensive root system for healthy growth and to maximise their resiliency during times of stress by ensuring that they have access to vital water and nutrients. In a poorly aerated soil pore size will be smaller as a result of wear or due to a loss of soil structure from compaction. As a consequence, there is less room for rooting and only limited space for air and water. Better rooting in a well aerated soil will also help grass plants survive during periods of hot and dry conditions
So the principal aims of aeration therefore are to:
- Relieve soil compaction
- Improve surface drainage
- Improve soil air supply
- Improve soil structure
- Improve conditions for rooting
- Promote the breakdown or organic matter in the upper profile
- Increase drought resistance (indirectly by encouraging deeper root growth and keeping the surface open to rainfall and irrigation)
What types of aeration can be done?
There are many different types of aeration but slitting and solid tining will probably form the main bulk of routine work.
Slit tines can be described in a variety of ways -depending on their shape and how they work: knife, diamond, chisel and root pruner. The slits are designed to penetrate the surface to stimulate rooting whilst maximising air exchange and minimising disturbance. Slitting is best completed during the autumn and winter period as slit marks can open during drier spring and summer conditions.
Solid tining is the operation of choice during the spring and summer. Solid tines come in a range of diameters and lengths but will produce a round hole which will not gape.
Routine aeration should be concentrated within the top 75-150 mm of the soil. The selection of equipment will depend on the size and quality of the area to be worked. Large amenity areas dominated by coarse grasses (perennial ryegrass, tall fescue and smooth-stalked meadow grass) are best treated with tractor mounted implements such as drum aerators fitted with solid tines (spikes) or slits. Tractor mounted implements are available for the full range of tractor sizes as well as for other utility vehicles to ensure that the work can be completed as efficiently as possible.
For smaller areas more compact, self-propelled, pedestrian aerators may be a better choice, particularly for ornamental lawns. These are available in drum and punch-action forms and can accept a range of tine sizes and types (slit, solid, hollow and spoon types).
For localised work hand tools (the garden fork) still serve an important function, especially for treating problems such as dry patch or localised drainage and/or compaction problems.
What about hollow coring?
Hollow coring is a more specialised operation; the physical removal of a core of soil from the profile with the aim of removing surface organic matter, poor soil and/or reducing surface compaction. Tine sizes vary from 6 mm to 25 mm diameter and generally have a working depth of 75-100 mm. This operation introduces a large volume of air into the soil profile and provides an opportunity for soil exchange. It would normally be directly followed by a top-dressing application; where a sand-based top dressing is spread over the area and incorporated into the open tine holes.
What about deep compaction? ?
Where a soil has become compacted resulting in drainage difficulties or a loss of structure has occurred due to work being undertaken in wet conditions, improvements can be achieved with the use of specialist equipment. Such implements are designed to be mounted to the rear of a tractor and come in a variety of sizes to suit all sites and ground conditions. The largest being around 2.5 metres wide and with a working depth of up to 400 mm (16 inches).
Machines such as the Verti-drain or Weidenmann operate in a similar manner as a hand fork where deep aeration of the soil profile is combined with a heaving action causing the fracturing and fissuring of the soil to depth to break up compacted layers. Other machines such as the Shockwave and Earthquake have a different mode of action but the end result is the same. These machines have a series of vibrating, rotating knives that create linear slits to depth rather than tines that leave individual, vertical holes.
The timing of deep decompaction work is vital to its success. The soil must be moist to maximise tine penetration but dry enough to allow the soil to fracture and fissure. Decompacting a wet soil will simply result in smearing and make cause more damage than good. If required, autumn is the best time to carry out this work.
Scarification is a different process to aeration; it is primarily a turf grooming operation, aiming to encourage an upright growth habit, remove untidy lateral/creeping growth, remove moss and control organic matter build-up. Scarification can be undertaken using a simple rake or chain harrow as well as with highly mechanised specialist scarification equipment fitted with a series of rotating vertical blades. Both pedestrian and tractor mounted units are available depending on the area to be treated. The choice of equipment should be determined by the area to be worked, intensity of treatment and quality of finish required.
The severity of a scarification operation will be determined by the extent of the problem to be solved. Routine scarification should only scratch the surface of the soil, removing moss and organic matter at the turf base. Deep scarification which penetrates into the upper soil profile is only required where excess organic matter has accumulated due to an imbalance in the maintenance programme. For example, over-watering or over-feeding, limited aeration, poor drainage can all contribute to an organic matter problem.
Scarification can be very damaging to the sward and should only be contemplated during periods of vigorous growth – spring and autumn. Spring work is integral for removing moss from the sward and reinvigorating growth. Autumn work on the other hand is very successful when completed as part of end of season renovation work with up to 3-4 passes being made to prepare an area for overseeding. In between, such work can be supplemented with more regular light raking. This will serve to maintain a good level of presentation when completed in conjunction with mowing as well as controlling the build-up of organic material at the turf base thereby reducing the requirement for very intense operations at other times.
Top tips for aerating and scarifying
- The timing of aeration is important. For fine, high quality areas, slitting should be restricted to the winter to prevent opening of slits during dry conditions. Deep decompaction needs to be carried out on moist soil to maximise tine penetration and thereby optimise the effectiveness of the operation.
- Ensure that the forward speed of the operation is set to optimise the effectiveness of the work being undertaken and not simply to finish the job as quickly as possible! If completed too quickly, penetration will be limited and there is a risk of ‘plucking’ the turf.
- Deep scarification is the most effective method of removing organic matter from the upper profile but has a limited working depth – usually 25 mm. The depth of operation should be limited to 75% of blade spacing to avoid destabilising the surface. If completing a double pass complete the second at half the working depth of the first and at an angle of no greater than 45 %.
- Where soils are heavy apply top dressing in conjunction with aeration to improve surface drainage, increase wear tolerance and dilute organic matter at the turf base. Cores should be no less than 12 mm in diameter to ensure they can be effectively back-filled.
- Only scarify when growth is strong to ensure good recovery. For a one-off annual treatment autumn provides the best option. Early scarification should only be completed once growth is underway (May) but never during hot/dry weather.
- Aim to vary the direction of scarification and complete when the turf is dry for a better finish. Avoid scarifying prior to lifting turf.
- Do not aerate/scarify within 2-3 days of applying a fertiliser to avoid disrupting the granules and potentially damaging controlled release products that may affect the release pattern. An application of a conventional product 7-10 days prior to work being undertaken will improve growth and will help ensure good recovery.