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Lawn Care
Deep Scarifying/Linear Aeration

© Brian Murdoch 2004

Brian offers some comments on this new-ish style of treatment which is a bit radical and some people may be a little daunted by the machines. Having used some of these machines, he thought others might find his experiences useful in reducing the "unknown" factor. He also offers a wealth of practical tips.

Our Problem.

  • The Meadows Croquet Club in Edinburgh has a green of about 3000m2 with a 40mm thatch layer which we inherited when we leased the site (originally two bowling greens) about 3 years ago. Profiles taken from various parts of the green clearly show the thatch layer. We are advised that this leads to dry patch and fusarium, apart from a slower playing surface. As we aim for a surface similar to a fast bowling green, this thatch has to be reduced and we have started to use linear aeration/deep scarifying to attack this problem.
  • And if you think that all that follows is a bit much, we have to apply £400 of wetting agent in the spring to counteract the dry patch consequences of the thatch layer and then have to be very careful to water the green during dry weather – and we have only a hose with sufficient pressure for one impact sprinkler – no irrigation system. Needless to say, this does not always get done – it takes a whole day to get a meaningful amount of water onto the green. So getting this thatch layer reduced is a worthwhile investment.
  • Having said that, as anyone who has done any amount of work on greens maintenance knows, there are no magic bullets or instant solutions to such problems. We anticipate three years before the thatch layer is significantly reduced, and it may take longer. One consequence is that a slightly less than perfect job one year will not have a significantly detrimental effect on the green.
  • Lastly, there is very little money in croquet, at the moment. Therefore we have to call on club members for the work involved in putting the green “to bed” in the autumn. Naturally we are constantly looking for ways of making the work easier, sometimes by acquiring machinery to help. Most of the machinery we have ranges from old to obsolete and survives on the application of much tender loving care. But it works well enough for the amount of use it gets. We do hire some modern machinery, and have a recently purchased a truly excellent 24” Allett Tournament mower.

First some quick notes about our situation.

Methods We Use For Preventing Further Thatch Build-Up

  • Sisis Rotorake
    Sisis Rotorake
    Sisis Rotorake with de-thatching blades – 4 hours per pass
  • Sisis Rotorake with thatch control/verticutting blades – 4 hours per pass
  • 4 foot wide Sisis grass comb mounted on our old Wheelhorse grass tractor. Very quick – effective at ripping up dead material and lateral growth – 45 minutes per pass.
  • Heavy (30Kg) drag brush pulled by Wheelhorse. Very quick for generally lifting the grass, especially lateral growth – 30 minutes per pass.

Methods Of Reducing The Thatch Layer

  • ½” hollow tining. Shall continue to use occasionally to depth of 100mm – right through the thatch layer and into the growing medium (rootzone) beneath.
  • Micro hollow tining to 50mm. Useful in the spring in that it improves air and water penetration and we don’t need to top dress afterwards – the tining holes are too small to have any effect on a rolling croquet ball. We use hollow tines as opposed to solid tines to help with thatch removal and so that the holes stay open longer.
  • De-thatching products, e.g. Rigby Taylor Syta-Thatch. No “on the ground” experience in local clubs that I have so far been able to contact. These products are quite expensive and their effectiveness may depend on application circumstances that are hard for the inexperienced to assess. We have no experience of using these products.
  • Deep scarifying. As a complement to the hollow tining above. Compared to ½” hollow tining at 2” centres, 2mm blades at 25mm spacing affects a larger proportion of the green surface at one pass – almost twice as much – although it does not go as deep.

Why Deep Scarifying In The Autumn?

  • We wanted to overseed as well, and without an irrigation system, we have found that overseeding in the spring does not work – the new grass plants do not survive the late spring and early summer dry spells.
  • We were very nervous about using this treatment in the spring because, with no irrigation system, we were afraid that the grooves would open up during dry spells before new root growth had time to bind across the grooves

Now to the actual work, almost!

Before You Start For Real

  • 1. The start of the deep scarification
    1. The start of the deep scarification
    Graden GS04 or Sisis R600? On local hire costs, the Sisis won hands down. On delivery, I checked the blades were fitted correctly – no problem. (Previous year they were fitted the wrong way round with predictable results – most of the tungsten tips were knocked out and many must still be lurking in our green. We hired from a different firm this year) .
  • How thick, how close, how deep? Despite many enquiries I found it difficult to get any clear advice on the relationship between blade width, blade spacing and working depth. Mind you, the hire market seems to offer 2mm blades at 25mm centres – you may have to hassle for anything else.
  • Avoiding overlap. If you overlap successive passes with these machines, you risk ploughing up the area overlapped. The R600 comes with a couple of supports for the collector box which we never use as the quantity of debris is so large. I tape a piece of wood across the supports and, sighting from the front of the machine, I mark the wood with the line of the outer blades – which seem to be slightly off-set. I then use these marks as a guide against the last groove of the previous pass.
  • If you have open areas adjacent to your green you will be able to work the machine right up to the edge of your playing surface and its maintained margins. We don’t and we have to think about finishing the “headlands” after the main work. If you overlap the main work when doing this, there is a risk of “cubing” or ploughing up the overlapped areas. It’s worth thinking about how you address this problem before you start doing anything. You may want to mark the limit of the main work to leave yourself a workable margin to finish off in a different direction to the main work.
  • As all mechanical work on a closely mown turf surface is hard on the grass, you should try to ensure that the grass is in a healthy growing condition before any such work. Otherwise the grass will take longer to recover from the work. We had applied the autumn fertiliser about 4 weeks before we did this deep scarifying and the grass was in quite good order.
  • I did a normal scarification a fortnight before the deep scarifying. I don't think that was a good idea - too much surface disturbance in too short a time.
  • Debris and sand/rootzone material
    2. Debris and sand/rootzone material
    Before doing the deep scarifying, you should cut the grass or you will find clearing up the debris afterwards very hard work. Also you will not get an even effect from the drag mat as you drag the disturbed soil back into the turf.
  • We experimented with increasing the depth of cut with the R600 until we found that the turf between the grooves was becoming too unstable – this was at a depth of about 25mm. The nature of the top layer of the green in terms of thatch, moisture content and root matrix obviously plays a role in how deep you can work. You have to be careful about the forward speed of the machine as well – we worked at gearbox setting 4. At 5, the cut was too ragged. In the end the depth of cut we achieved was a bit under 25mm.

And Now, The Actual Deep Scarifying

  • Friday October 8th was dry. Switched dew off surface. Deep scarified the green (3000m2) in about 6 hours – see Pic 1. We would probably do better next time – you gain in confidence as you use machinery like this. Large amounts of debris were pulled up and a great deal of sand/rootzone as well. Do we really need to lift all that sand and pay to have it hauled away? See Pic 2.

That’s It! Now For The Resultant Debris

  • Rumbling the debris with the drag mat
    3. Rumbling the debris with the drag mat
    Saturday was debris removal day. Let debris dry off for an hour in the sun (lucky us). I thought about this mix of sand and thatch and decided to shake out the sand with the drag mat. Amazing!! – but probably no surprise to old hands at green keeping. Rumbling the debris with the drag mat shook the sand out of the mix and rolled up the fluffy thatch debris into sausages – see Pic 3. Truly, all that was left was what we needed to remove – with very little green grass content. And the total quantity of debris to collect was reduced to below 50% and weighed practically nothing at all – see Pic 4. Try doing that with ½” hollow tining cores.
  • Gathering the fluffy thatch debris. We tried various processes – rakes, snow shovels, blowers, but I feel that in the end rakes and snow shovels were perhaps the best. The problem with blowing the debris into heaps was the tendency to blow up the sand, especially fines, as well as the thatch, leaving a heavier layer of sand in patches on the green. It’s as well to remember to work in the direction of the grooves when using tools that are likely to catch the edge of the grooves – e.g. rakes, drag mats. Next year I’ll try to get hold of wide rakes, but they’ll have to be quite light or the arms of the club members will not survive.
  • Having removed the bulk of the debris, we dragged the green again to drag the loose sand into the turf. For a final clean we took out an old Ransome 24 and adjusted the height of cut to avoid picking up sand and then mowed off the remaining debris. And very good it looked too. This had the additional benefit of smoothing down the surface prior to top dressing.
  • Over the next few days we overseeded and top dressed the green. To work from side to side of the green – about 85 yards – we had to load our top dresser with ¼ tonne per pass. Despite the grooves making the ground feel softer, there does not seem to have been significant rutting by the sand spreader’s tyres. We dragged in the top dressing along the line of the scarifying grooves. I then took out the old Wheelhorse tractor, hitched the drag mat to it and did two complete passes of the green at 45 degrees to the grooves.

Follow-on Treatment

  • I think in the spring we’ll micro tine the green again – it all helps to remove thatch and improve air penetration. Being small cores, rumbling them with the drag mat is partially successful in dispersing the sand content before collection.
  • Next autumn, I’ll try to hire a deep scarifier with wider set blades – say 40-50mm – and cut down to the base of the 40mm thatch layer, working at 45 degrees to the direction of this autumn’s work.

Additional Remarks

  • As we rumbled all the sand out of the debris from this work, I wonder whether we need to top dress? Next year I might be tempted to spread grass seed and drag the lot into the surface of the green. After all, apart from a heavier dressing, what is extra top dressing going to provide in addition to the sand/soil rumbled out of the debris? And it would save us a great deal of cash and work.
  • Debris with the sand rumbled out of it
    4. Debris with the sand rumbled out of it
    The concept of the top dressing penetrating the grooves in the soft ground after so much machinery and foot traffic (had effectively closed up the grooves) is a bit of an illusion, at least in the short term. The winter rains may wash it into the grooves – time will tell. But the theory is that better air and water penetration will help the natural decay of the thatch layer and promote root growth. Mind you or ground was quite soft after much rain, although we were very lucky to grab the few dry days to actually get the work done. If the ground was drier, this closing up of the grooves might not be quite so pronounced.
  • One thing that I will probably try next spring is to break up the hollow tining cores using the normal scarifier with its blades set to just touch the soil/thatch surface. This might kill two birds with one stone – reduce the volume and weight of core debris to be collected and give a light surface scarify.
  • One part of the green overhung by a tree has very weak root growth and the machine did pull up the turf in a few places – see Pic 5. Anyone any ideas (short of felling the tree) for alleviating this problem?

More On Debris Collection

  • Turf damage where the root growth was weak
    5. Turf damage where the root growth was weak
    I don’t apologise for going on about this – making this as easy as possible is a key part of completing the work satisfactorily without reducing our members to hopeless physical wrecks who can’t even summon the energy for a pint afterwards!
  • The effectiveness of all of the stages in deep scarifying probably varies a great deal depending on the weather and moisture content of the ground. Deep scarifying in wet ground will work and may not be very affected one way or the other in ground with a very high sand content.
  • The problem comes with removing the debris. I was so impressed by the effectiveness of rumbling the debris with the drag mat in the reduction in volume and weight of the material to be removed, that I would be extremely reluctant to do the job again if there was not a high probability of good weather to dry the debris. Not only does this make the task of removing what needs to be removed much quicker and lighter, you have less to dispose of and if using a skip, one about a third the size will do - saving cash.
  • Further, if you drag the disturbed sand/soil back into the green, you will certainly be able to reduce your top dressing, or even better, do without it altogether, making for a huge saving in cash and effort. Using bagged and dried top dressing for our green costs £800 and takes about 12 man hours to apply - and we have a top dressing machine. Using barrows and shovels hardly bears thinking about over such a large area.
  • I am not suggesting that you can do without top dressing indefinitely but you may be able to go for a year or two without and use the cash for other things - like regular overseeding to improve the grass species mix.

Caveat

All of the above are the observations of an amateur – we buy in professional advice on a regular basis.

I hope this will help anyone else who is contemplating using one of these deep scarifier/linear aerator machines for the first time, although you will obviously have to interpret the above in the context of your own ground conditions. It would be very useful if those who have used these machines before could share their experiences as well. Also any other comments would be most welcome.

Brian Murdoch

Scottish National Croquet Centre
Meadows Croquet Club
Edinburgh
www.meadowscroquet.org.uk


Author: Brian Murdoch
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Updated 28.i.16
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