Thatch

Welcome to the Thatch course.

Please study all the information below, understanding every element of Thatch. When you have finished studying, take the test.

Lesson Notes

Thatch - Study all thatch associated issues and causes

When - Understand when and where thatch occurs

Control - Study how to control thatch in turf

WHAT

The latter half of the 20th century saw a huge improvement in people’s living standards. This included better wages and an increase in disposable income as well as a reduction in working hours with the standard 40-hour week becoming the norm. Although competitive sport had been played for many years prior to these times, spare cash and spare time allowed many more people to indulge in their favourite sports either as a competitor or spectator. Many of these main sports were taking place on natural turf surfaces such as golf, football, cricket, rugby and tennis to name but a few.

Increased salaries, TV rights and advertising bought more and more money into these games. This in turn filtered down to offer bigger budgets to groundsman and green keepers who, with many technological advancements were now able to provide ever better playing surfaces. However, this in turn created ever increasing pressures to provide immaculate surfaces and the demands and expectations from players, spectators and sports turf managers continued to grow.

Regardless as to the sporting discipline, there are a myriad of maintenance regimes and techniques involved in keeping sports turf surfaces to a high standard and to discuss any of them in detail is far too big for this session. The purpose of this report is to concentrate on an issue that requires large budgetary and labour resources to keep in check and that is Thatch! Thatch accumulation is without doubt one of the most common and challenging turf related problems experienced by today’s sports turf managers.

For the purpose of this session, golf greens will be the main focus. Whilst all sports turf surfaces are susceptible to thatch accumulation, golf greens for many reasons (mainly a combination of unbalanced maintenance regimes and age) are the best exhibitors of thatch.


What is Thatch

In general thatch can be defined as the brilliant James B Beard remarked as “a tightly intermingled layer of partially decomposed dead or dying stems, roots and shoots that form between the zone of green vegetation and the growing medium – soil surface.” Thatch is also occasionally referred to as fibre. This organic horizon can build up into a spongy layer consisting of carbon-based compounds such as lignin, Cellulose and Hemicellulose, all of which are present in different levels in different grass species and all of which have different rates of decomposition. Lignin is vital in water transportation and is therefore naturally hydrophobic (if it’s going to move water about the plant then it has, to be waterproof). It is worth pointing out at this stage that there are two types of thatch.

image: https://extension.umn.edu/lawncare/how-control-thatch-your-lawn

Fibrous Thatch

Resembling Coconut Matting which is tough wiry and brown in colour which is high in lignin and generally found in root zones dominated by the slow growing species such as fescue, brown top bent and smooth stalked meadow grass and is generally found in the high sand-links environment.

Spongy Thatch

This type of thatch tends to be more of a yellow brown colour and softer than the fibrous type, with black streaks that identify anaerobic bacterial activity a precursor to black layer (a whole new subject for another session). Probably smelling stagnant, this thatch layer develops under waterlogged conditions where fine textured soil makes up the majority of the root zone and Poa annua is the dominant species. It is worth pointing out that this type of thatch can be found in coarse textured root zones too, however they are likely to have been overwatered overfed and still Poa Annua dominated.

Whilst slightly different in appearance and physical characteristics of both of these layers have an impact on the playability of the turf surface and can bring a plethora of other issues.

What are the issues and disadvantages relating to thatch

It should be pointed out at this stage that any negative issues resulting from or relating to the thatch – fibre layer are wholly dependent, on the thickness and depth. Enough scientific data exists to support the statement that “a limited amount of thatch is desirable” for several reasons including recycling of nutrients, protecting the soil surface and protecting the crown of the plant. There seems to be a general, consensus that a 5-10 mm layer of thatch can be beneficial but anything over 10 mm starts to become an issue.

Surface water retention

During periods of prolonged wet weather, compressed fibre acts like a sponge, holding water close to the surface. This in turn creates spongy - soft playing surfaces especially evident on golf or bowling greens causing slow ball roll. This also leads to foot printing not to mention inaccurate heights of cut on mowing machines due to cutting cylinders sinking into the soft surface therefore bench setting of mower is not reflected on the green this can cause scalping and moss and disease ingress. These waterlogged conditions also create anaerobic conditions where oxygen requiring, thatch munching bacteria stop working and although anaerobic bacteria feed on thatch, it is at a much slower rate so the thatch decomposition in waterlogged conditions is glacially slow.

Water movement

The same water retention as above not only has its disadvantages in the wetter winter months but also causes problems during the Summer months when that same thatch layer becomes hard and crusty and impedes the movement of much-needed irrigation water. Quality wetting agents can help penetrate the thatch layer however this would only be treating the symptoms and not the problem.

Fungal Disease

Thatch is a perfect environment for several diseases causing fungal pathogens. Microdochium patch and Anthracnose foliar blight being the most commonly experienced. These saprophytic fungi (feed on dead and decaying matter such as thatch). Thatch holds on to moisture which fungi also need in order to successfully complete their life cycles. It is not coincidental that playing surfaces with a high thatch content are also highly susceptible to fungal disease incidence. Additionally, the organic rich habitat present in thatch is also an ideal environment for the development for the several types of fairy rings (Basidiomyces sp.)

Crown Elevation

As the thatch layer increases it elevates the crown of the plant, so it is no longer in contact with the root zone. The crown of the plant is responsible for many functions within the grass plant and its proximity to the root zone is vital. https://archive.lib.msu.edu/tic/tgtre/article/2000may1a.pdf

Nutrient availability

Thatch can act as a physical barrier that actually impedes the downward movement of applied fertilisers stopping them getting to the root zone to be broken down and made available to the plant’s roots.

Extreme temperature tolerance

Excessive thatch accumulation physically retards the downward movement of plant roots. This leads to the majority of roots being found closer to the surface which are then exposed to the extremes of heat and drying out potential in the height of Summer or the threat of ice kill or a desiccating wind in the Winter.

Pesticide movement and degradation

Most modern plant Protection Products are carbon based and require carbon munching microbes to consume the residue, left in the soil after the product has done the job it was intended for. The spongy nature of the thatch can absorb and hold on to some of these chemical residues keeping them in the Ecosystem longer than they should actually be. Many Products are also systemic in nature and need to be taken up by the roots in order to be translocated around the plant. If the thatch is interfering with these products getting to the roots, then their effectiveness is seriously compromised.

Pest incidence

Several species of insect larvae such as Leatherjacket, Chafer Grub and Cutworm utilise the thatch layer as their living ecosystem. These insects not only feed on thatch but also on living root and shoot tissue leading to visual turf damage. The deeper the thatch layer potentially sees a greater number in the pest population. This can have a secondary problem with Corvid bird species pecking and damaging in search of these grubs.

Restricted root development

The plant struggles to physically develop deep vertical roots through the fibrous nature of the thatch forcing the roots to grow sideways known as bridging roots. This causes the majority of roots to be confined to the top 20 mm of the turf profile which not only leads to an unstable turf surface but makes the plant exceptionally susceptible to Hydrophobicity and localised dry patch. Shallow roots are also highly prone to the cold desiccating winter winds and cold temperature stress

Seedling development

A deep thatch layer can adversely affect the development of seedlings that the Greenkeeper may be trying to overseed into an existing sward. The tiny new roots struggle to penetrate the fibrous layer and therefore do not come into contact with the soil-root zone which is vital.

WHEN

Thatch accumulation occurs when the rate of production of organic matter is faster than the rate of its decomposition” (Beard, 1976; Beard and Green, 1994)

Root zones of sports playing surfaces are in a constant state of flux and go through constant dynamic changes influenced mainly by the growing life cycle of the plant, which for the sake of this report is generally from March to November in the UK. Many shoots, leaves and roots die off throughout the growing season contributing to the depth of the thatch layer that accumulate up to 5 mm in depth in one growing season.

During the growing season when soil temperatures are suitable, carbon munching – thatch degrading bacteria and microbes are busy consuming this build-up of thatch. Throughout the cooler Winter months, the accumulation rate of thatch slows down considerably due to the fact that the growth rate of the grass plant has slowed into its dormancy period. However, due to colder soil temperatures the microbial activity of the thatch munching bugs also slows considerably. Therefore, Winter sees a bit of a stasis period where thatch production and degradation doesn’t really take place.

WHERE

In short, excessive thatch build up occurs in an environment that is out of balance, where accumulation is quicker than decomposition. It is not a coincidence that less intensively managed sports turf areas such as golf fairways or lower level football and rugby pitches and cricket outfields develop far fewer levels of thatch. The soil ecology in these areas has found its equilibrium where the micro flora and fauna are working efficiently. These areas are not subjected to the same levels of mechanical and compaction stresses or chemical, nutritional and water inputs as more intensively managed areas such as golf greens.

Modern day greenkeepers are under constant pressure to ensure the best putting surfaces possible and can sometimes be a little overzealous with the maintenance regimes carried out. Many of these maintenance procedures are well intended, however, when carried out without proper testing parameters such as Clegg hammer, nutrient testing and moisture meters then the balance can be tipped, and the decomposition rate can’t keep up with the accumulation rate. Another reason for the tipped balance can be where inexperienced staff are allowed to make these important maintenance decisions or volunteers at bowling greens for instance where well-intended help can lead to problems.

WHY

Excessive Nitrogen

Stimulates rapid shoot growth which leads to thatch accumulation. High rates encourage shallow roots which increases lignin content within the thatch layer. Too much N can upset the Carbon/Nitrogen ratio which will have an effect on the decomposition rate. Plants will only use what they need. Soil nutrient testing will allow for the correct decisions to be made regarding fertiliser applications. However, Nitrogen does not feature in standard soil analysis; this is due to the many climatic, chemical and biological factors that influence the amount of N in a soil at any given time. Soil Nitrogen levels can fluctuate rapidly, and a tissue analysis of the plant is the only real way to monitor N requirements.

Excessive Phosphorus

Stimulates rooting at the area where the roots come into, contact with the nutrient. This creates an abundance of roots within the thatch layer.

Over watering

Stimulates rapid shoot and root growth within the upper horizon adding to the thatch issue. Excessive irrigation maintains a high moisture content at the expense of Oxygen once again decreasing decomposition rates. Frequent light irrigation programmes should be replaced with infrequent longer cycles that allow water to properly move down into the rootzone

Compaction and Aeration

Compacted root zones due to lack of Aeration or the use of fine sand materials during construction or subsequent topdressing operations lead to oxygen poor waterlogged conditions. This as previously mentioned is not an environment that thatch consuming microbes can thrive.

Excessive use of Chemicals

Many plant protection Products (not so much today) are or certainly were toxic to beneficial soil microbes. Over-use of these chemicals had very damaging effects on the soil environment and its ability to degrade thatch. Certain species of Fungi are responsible for the decomposition of the tougher components of thatch such as Lignin and cellulose. Fungicides applied to control surface forming diseases also have an effect on these beneficial Fungi. Historic over use of highly toxic wormicides were also associated with rapid thatch build up.

Organic Top Dressing

Sand containing high rates of organic matter will add to the thatch accumulation rate. Many of these organic components in some topdressings are often composed of compounds such as lignin and cellulose.

Fine Textured Sands

Topdressing with fine materials will impede drainage by blocking up macro pore spaces. This in turn creates a moisture rich low oxygen environment which limits the action of composting microbes. Fine particles also impede root development resulting in a greater accumulation of roots closer to the surface and an increase in thatch accumulation.

Lack of drainage

The Root zone used during construction and the subsequent topdressing materials and maintenance techniques may all be ideal. However, without any proper subsurface drainage installation at the time of construction a green will always struggle. Without the ability to get rid of excess water the root zone during times of high precipitation will gradually become waterlogged and go into an anaerobic state once again limiting the action of aerobic microorganisms required for thatch degradation.

Grass species

Certain species and newer turfgrass varieties with increased vigour and density produce more organic residues that form the thatch layer. Low growing, prostrate species such as creeping bent form more thatch than upright species. However, thatch produced by upright species such as some of the fine fescues have very high lignin content which is exceptionally slow to decompose. However, many of these species have a slow growth rate and therefore develop a correspondingly low rate of thatch accumulation.

Club decisions

This should not be underestimated in the process of thatch accumulation. Management or club officials that overrule the greenkeepers decision on vital maintenance must take responsibility for a reduction in sports turf quality. Changes made to the maintenance calendar in favour of not disappointing members or for fear of losing a lucrative visiting society is often an issue experienced by many Greenkeepers. Short term financial benefits are overshadowed by a postponed maintenance operation. Club management will invariably offer an alternate date which will always be in late Autumn which is far from ideal.

pH

Extremes in soil acidity or alkalinity have an effect on the functionality of soil bacteria and microbes. pH testing is a regular feature of normal soil nutrient tests and a good way of checking that maintenance regimes such as fertiliser usage or irrigation water or top dressing is not altering the pH dramatically enough to create any issues.

Grass clippings

Prolonged clipping return to surfaces can be considered to adding to Thatch however this is minimal due to a low amount of Lignin component being in leaf tissue

HOW

Whilst it may appear obvious, but not allowing thatch to build up in the first place is key. Assessing current levels and the current maintenance regimes that are in place will help to make informed decisions as to the level of control that needs to be adopted. Testing procedures such as the following will help to quantify parameters.

  • Assess nutrient levels via soil testing this will stop over application of fertiliser.

  • Make sure spreading equipment is properly calibrated to avoid over application.

  • Regular use of a soil moisture meter will allow for better timed irrigation cycles

  • Ensure irrigation system is working correctly to avoid overwatering

  • Get irrigation water periodically tested to test quality

  • Periodically get topdressing tested

If thatch has become a recognised problem that is starting to create some of the issues mentioned above, then increased mechanical management will have to be adopted. Aeration in one form or another and applications of a suitable-compatible top dressing applied over the growing season is crucial to efficient thatch management.

The amount of fibre removed by Hollow Tining is more important than the amount of times this process is carried out, so the size of tine and pattern are very important factors to address (see Table 1.) This can also be said of topdressing with the advent of new spinner type top dressers and the current vogue of little and often can be that over the season nowhere near enough dressing has been applied and the thatch remains compressed and undiluted. This little and often approach magnified by greenkeepers often led by committee members not wanting to disappoint the golfers or not wanting to dull cutting units. However, dumping large amounts of sand on golf greens in one go also creates its own problems. A general guide seems to be two Hollow Tining operations carried out in the season one in Spring and one in late summer. Each operation requires 40 tonnes of dressing based on the average 1 Ha of greens to fill in the holes. Regular light dressing to be carried out throughout the season makes up at least another 40 Tonnes therefore a minimum of 120 Tonnes is desirable.

Table 1. Varying types of tines and spacings and the % of surface area impacted

To ensure optimum recovery, growth potential should be at least 50%>. Use Amenity Weather to perfectly time thatch removal operations and optimise healthy recovery.

Combining topdressing with one form of aeration or another is crucial for mixing the sand into the fibre layer and thus diluting it. Simply applying sand to the surface and allowing the grass to grow up through it will lead to root break in future years. Alternating the depths and types of Aeration operations is also prudent. Tining at the same depth can actually lead to a pan forming further down in the profile. Varying depths de-compacts the profile and facilitate good drainage and Gaseous exchange.

Finding the right time to aerate is always challenging especially with a packed sporting calendar. However, Hollowtining in late Summer / early Autumn is ideal due to good soil temps and the advent of more moisture and low levels of stress. This combines to ensure a swift recovery time as quick as 10 days. Waiting until October as traditionally carried out when the so-called golfing season is coming to an end is fraught with issues. It may be too damp to get the sand into holes. Smothering the grass with sand at that time of year increases the likelihood of fungal disease attack. Slow growth means that holes will probably be seen right through the Winter into the following Spring which in turn means a bumpy putting surface.

Hollow tining

Easily recognised as the most efficient and successful form of thatch removal and sand exchange. This mechanical machine utilises cylindrical hollow metal tubes – tines that punch holes into the surface and pluck out a core of that comprises thatch and root zone. Modern machines allow for a wide range of different sized tines as well as being able to alter tine pattern and spacing as well as hole depth. Cores can also be broken-smashed up before collection; this helps to separate sand and thatch allowing for expensive substrate to be reused to fill in the holes.

Top Dressing

Example of a modern topdressing machine fitted to one of several utility vehicles available to Greenkeepers-Groundsmen. These machines allow for efficient and accurate sand applications. With many different settings available to alter application quantities.

Scarifying

This process relies on vertical blades that enter the soil profile to provide a linear Aeration technique, dragging out thatch and organic matter. Topdressing is beneficial afterwards as is overseeding. Depth settings can be altered although caution is recommended as Scarifying can be quite aggressive and injure roots substantially if over used. Scarification does not remove half as much Thatch as hollow tining and should be considered as a complimentary maintenance procedure alongside hollowtining.

Graden

This machine is relatively new within the industry (10-15 years) and should probably be regarded as a heavy-duty scarifying machine that also has the ability to inject dry kiln sand directly into the grooves left by the linear blades. There is also an overseeding attachment, so it appears to be all things to all men especially as different thickness blades can be selected. It is loved by many due to minimal surface disruption and a definite firming of the surface allowing return to play rapidly. Many saw this as replacement for the disruptive Hollowtining machines however it is worth pointing out that this machine is very labour intensive to use and still does not quite compete with traditional hollowtining methods as illustrated by the ISTRC Displacement Chart (follow website) extreme caution should also be followed when using this machine on shallow rooting Poa annua greens.

Verti-cutting

Whilst much may regard Verti-cutting as a form of thatch removal, technically it is more about grain control and moss removal. A very shallow version of scarification with thinner blades at closer settings this machine is only designed to scratch the turf surface rather than entering the thatch layer. Designed to speed up the surface and remove lateral growth. There is a case that verti-cutting enables higher oxygen ingress into the root-zone therefore facilitating the Aerobic microbes and their thatch munching mission.

Koro

This machine really is only utilised when the thatch layer has got to a thickness point of no return, where no level of hollowtining or scarification will restore a balanced root zone. This machine has been utilised by higher league football clubs for a while now and is used to remove the pitch at the end of the season before spreading a new root zone and overseeding. Cricket groundsmen may utilise this machine every few seasons when wickets start to get a little soft and the bowlers start to complain. However, it is also starting to be employed by Golf clubs more and more when they have the occasional problematic green. The machine strips off the vegetation and thatch layer to a predetermined depth leaving a naked root zone that can be slightly loosened up and top dressed, not too much however as altering the contours of the green may change the playing characteristics of that particular green. Then the green can be seeded or turfed.

Biological

There are companies on the market that offer biological products that are sprayed to the turf surface that contains Fungi that feed specifically on thatch

SUMMARY

Thatch occurrence is a sign of an ecosystem being out of balance e.g. accumulation is occurring at a faster rate than the soil microbes, ability to break it down. Finding the correct balance for your particular site is crucial when deciding what form of maintenance regime to follow. Regular monitoring with a soil profiler is wise as is regular soil testing and frequent use of a Clegg hammer and moisture meter. This is especially important as different turf surfaces within the same site may differ significantly for example it is quite common for a few greens to exhibit different thatch levels compared to the rest on the same golf course.

Effective thatch control must include a sound maintenance programme which fits both the type of surface being prepared and the level on which it is being maintained. A good turf management program includes preventative practices that reduce thatch accumulation and curative practices used to remove the excess.

  • Do everything possible to make the soil-root zone environment conducive for thatch degrading micro-organisms to flourish e.g. adequate aeration, avoid overuse of the irrigation system, monitor pH and avoid the overuse of Plant Protection Products.

  • Avoid indiscriminate use of fertilisers in regard to frequency, timing and rates.

  • Twice yearly hollow tining to control normal thatch formation. Ensure this is done at suitable times of the year when recovery will be swift. Set the dates in the club calendar in stone.

  • Topdress with appropriate dressing to dilute thatch layering. Use sand that has the closest particle analysis to the root zone on that particular turf surface.

  • Use vertical mowers (scarification) in addition to hollow tining when necessary.


Thatch management should not be an occasional practice and should be the backbone of most annual maintenance plans. Relying on sound cultural practices which encourage organic matter degradation rather than thatch accumulation. This will contribute to healthier playing surfaces which increases playability and reduces maintenance costs.