Poa to perennial

The second article by Martin Ward, MD of Symbio on the new science of how soil biology can help greenkeepers transition their swards from annual meadow grass (Poa annua) to the perennial fine grasses, the fescues and bents to improve green surfaces performance and reduce costs.


Effecting a stress free change to perennial grasses


poa annua, fescue, bents, fine grasses,

Stressed annual meadow grass (Poa annua)

This sounds too good to be true, nevertheless it is possible to convert playing surfaces from predominantly annual meadow grass (Poa annua) to predominantly fine grasses without going through a period of deterioration in putting performance – the solution starts with the microbial life in the rootzone.

Natural plant species progression has evolved so that almost all sterile bare ground is colonised first by annual seeding grasses like Poa annua and tap rooted weeds and then progresses through early perennial grasses to fine grasses such as fescue and agrostis(bents). If left uncut it would eventually become forest.


Sports turf management versus nature.


Why is it that natural selection will invariably start with Poa annua and progress to perennial grasses while in sports turf management we often start by sowing perennial grasses (fescues and bents) and progress to Poa annua? 

poa annua, fescue, bents, fine grasses,

Seeding Poa annua among fine fescues

The answer is that modern sports turf soil is specified and managed in such a way that it becomes almost sterile just like the soils designed to be colonised by Poa annua.

Most perennial grasses release about 50% of the energy they produce above ground and about 50% underground as root production and by leaking proteins and carbohydrates as root exudates. This energy feeds the underground food chain of bacteria, fungi, protozoa, nematodes, arthropods and worms, this chain is known as the soil food web. 

While Poa annua is programmed to live in ‘poor bacterial’ dominant rootzones, fescue and bent grasses need a balanced ratio of soil bacteria and fungi in their soil food web to survive.




There is a very important group of fungi that live inside the roots of the grass. These fungi are called mycorrhizae, which means fungus root. Mycorrhizal fungi act as an extension to the root system of perennial grasses extending their hyphae into the soil. They produce enzymes that make phosphate and other nutrients available and then transfer the nutrients, trace elements and water in available form to the grass plant extending the effective root area many times. 

poa annua, fescue, bents, fine grasses, mycorrhiza

Mycorrhizae around grass root

This activity goes on all the time in unfertilised grasses which explains why you never have to feed the rough on a golf course and it is nearly always made up of a higher percentage perennial grasses. 

Unfortunately non-‘traditional and natural’ greenkeeping practices that have come in since the 1960s, now usually include the use of

1) inorganic fertilisers, (which are mineral salts),

2) fungicides, and

3) copious irrigation,

4) coupled with lack of aeration,

and have severely reduced the fungal populations in the thatch layer and rootzone. 

When fungi die thatch starts to build up, thatch holds more water, reduces oxygen availability, promotes disease and a vicious cycle of fertiliser, water, fungicide begins, creating the ‘poor bacterial’ dominant rootzone favoured by Poa annua. 

Naturally occurring thatch degradation by fungi and bacteria is extremely important for growing perennial grass. When thatch degrades it produces humus, humic and fulvic acids, which apart from being essential plant foods ensure a slightly acidic pH around the root system, which is what fungi need to survive, even within a wider alkaline environment of chalk downland or shell based links.


The solution.



Until you get the correct soil biology for fine grass, over-seeding and any physical or chemical remedy for Poa annua control will be continuing and costly. Get the right soil biology and Poa annua will convert by itself to perennial Poa and eventually fescue or bent depending upon over-seeding, indigenous grass species and your greenkeeping management practices. 

80% fescue 20% bent grasses

Beneficial fungal and mycorrhizal populations may be quickly built in the sward and rootzone by using low salt index or organic fertilisers, and applying the fungal biostimulants. Fungi may also be introduced to breakdown excessive thatch levels. 

When the soil biology that supports perennial grasses has been created you often find that the old seedbed springs back to life and colonisation by fescue or bent grasses occurs. You will also start to see markedly better results from over-seeding and the conversion to fine turf will begin.


Martin Ward, who gives this second article explaining the subject to non-experts above, is Symbio’s MD and has led his company to provide advice to a wide number of golf clubs over the last 23 years. He is very happy for greenkeepers or Chairmen of Green to ask his advice about specific issues concerning their own courses.

Do be in touch directly: martinward@symbio.co.uk     + 44 (0) 1428 685762  

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