In a previous article I detailed the 3 guiding principles for greenkeepers hoping to set their greens up for high performance consistently, before setting out some practical measures that can be adopted to ensure success.

We finished up by briefly touching on Public Enemy Number 1 when it comes to poor bowling surfaces…Thatch. So today, I’d like to detail some practical methods for reducing thatch quickly.

However, before we do that I’d like to clear up some of the misunderstanding that exists in the bowling world about thatch, by taking a moment to explain what we are dealing with here.

What is Thatch?

Thatch is the layer of dead and decaying organic matter such as old grass plant shoots, roots and leaves left behind by individual grass plants as they grow and develop. 

If you go to a wild meadow or un-managed field of grass and take a sample of turf, you will find at most a thin layer of fairly loose thatchy material. This will easily allow water and air through into the soil and the overall picture will be one of a healthy living eco-system.

There will be a dense sward of grass and other plants. In this setting, the only sources of added nutrition apart from that readily available from the soil are the nutrients released by soil organisms such as earthworms and billions of soil microbes acting on the thatch layer (natural decomposition), animal droppings and nitrogen fixed from the air by plants such as clover. 

The thatch layer is actually a key component in the make up of a high performance bowling green. However, in contrast to the situation described in above, as greenkeepers we are producing an essentially unnatural environment.

We are trying to encourage very dense populations of just one or two plant species and attempting to exclude all others. In addition to this the finer grasses that we are trying to encourage, and the bent (Agrostis) grasses in particular, tend to produce thatch very quickly. This combined with a history of intensive management, including sustained and routine use of chemical pesticides and fertilisers makes the majority of bowling greens heavy producers of thatch. 

As we saw in July’s column when we discussed the Circle of Decline, this results in an increased reliance on fertilisers and chemicals to sustain any kind of growth as the excessive thatch results in anaerobic conditions, a sharp decline in soil microbe populations, which leads to reduced efficacy of the very fertilisers and pesticides we rely upon. Dense thatch usually appears alongside compaction in the soil.

Unfortunately the thatch that builds up on bowling greens does not break down either rapidly or readily in the conditions we produce. Firstly the thatch builds up very quickly, so that it is not unusual to find 50 to 75mm of thick, dense thatch on a poorly performing bowling green. Secondly, this dense thatch does not break down readily by natural means, due mainly to the relatively low populations of soil microbes, low soil pH and the generally inert and lifeless nature of these soils.  

If we are to have any chance of success we must start the process of green recovery by taking charge of thatch reduction ourselves. 

In the green renovation phase we are mainly concerned with the physical and quick reduction of the existing thatch layer, A process that will create vastly improved soil conditions and will encourage the increase of soil microbial activity. 

Thatch Removal Methods
There are various methods used to reduce thatch quickly, some old and immediately recognisable and some not so familiar but very effective methods, which have been introduced in more recent times.
The majority of this type of work is best performed at the end of the bowling season in the autumn while the there is still growth and some heat in the soil to aid recovery.

Depending on the severity of the work required there are two basic methods we can use and these are some variation on scarifying and the old favourite, hollow tining (coring). 

Hollow Tining.
Hollow tining (coring) equipment has improved dramatically over the last 20 years or so and is now a fairly efficient method of removing dense thatch. However, it should be noted that even with the latest, vertical entry machines and  jumbo tines at close spacing, this method will remove at best about 5-6% of the green surface area. 

The best aspect of hollow tining as part of a program is in its ability to puncture a hole right through the entire depth of the thatch layer allowing a connection with the underlying soil. Something that even the most severe scarification fails to do in many cases. 

However, as a method of reducing thatch quickly, hollow tining should usually be combined with heavy duty scarification or slotting as it is sometimes referred to. This is a very severe operation and not the usual type of scarification seen around the greens throughout the year. 

Slotting or Heavy Duty Scarification
In the last 20 years or so we have seen the gradual introduction of machinery capable of very deep scarification and as a result very high levels of thatch removal.
The machinery typified by the Graden GS04, although other brands are now available, can easily remove 15% of the green surface, without the loss of any significant amount of soil. 

This method should be regarded as part of a renovation program and will probably not be carried out for more than 3 years in a row without a rest.

However, using this method combined with hollow tining as described above we can now predictably remove over 20% of the green surface during an intensive renovation program. 

Depending on the severity of the thatch problem a variation of this program is likely to yield the best results for most greens in renovation phase i.e. those that have signs of being in the Circle of Decline and which are performing poorly.
The program must be carried out in the autumn, when there is still sufficient heat and the likelihood of sufficient moisture to aid recovery before the onset of winter. 

The program will probably have to be repeated on at least one further occasion in subsequent years. However, the overall effect is much greater than the immediate 20% reduction in thatch. Due to the huge volume of air introduced to the green surface during this process, the microbial activity in the green can be expected to increase dramatically and therefore that natural recycling of organic material into valuable humus will be increased as a result. 

An autumn program like this can lay the groundwork and give impetus to a sustained recovery program for even very poor greens, allowing them to start to recover their natural vigour. 

As part of a planned transition to the Performance Bowling Greens Programme, this approach will start the recovery many thatchy, compacted and poor performing greens need.

Such a programme can be the catalyst for breaking the dependency on chemical pesticides, excessive fertiliser applications and start the recovery from common disorders like Localised Dry Patch and frequent fungal disease outbreaks.