Updated: Apr 13, 2020
I took myself out for a goodly 5m hike for todays allocated exercise and to brush up on my botanising.
Here's one member of a patch of Field woodrush (Luzula campestris) scattered across the green in Ayot Green, Hertfordshire..
I am fond of this little guy. I like his yellow and russet head and the long messy hairs on his leaves. I like his diminutive size. He is small and neat, where rushes are usually large and bulky.
I am not fond of how he is referred to on many blogs as a "nasty lawn weed that's impossible to get rid of". It's a great little plant that can invade my lawn any day!
Field woodrush can be an indicator of nutrient poor, moderately acidic soils (Biological records centre, n.d) and can be an additional indicator of historic acid grassland or heath
But before you exitedly start wondering if your front garden was part of some ancient park, this is a common species that can pop up in any undernourished lawn or playing field. It can also tolerate mildly alkaline soil (Biological records centre, n.d) and may pop up in nutrient poor chalk grassland.
A quick scan through google seems to reveal a disagreement between sources as to whether it is typical of highly acidic soils or prefers soils closer to neutral.
Mabbet (2009) and The Royal Horticultural Society assert that acidification of topsoil through poor management and environmental means is a more important factor than native soil pH, particularly in calcarious grassland.
(If anyone can contribute with reputable knowledge and citations, I'd be appreciative).
All that considered, please don't consider it an "absolute" indicator of acidity or history.
You need to use your knowledge of the local area to ascertain whether or not it's likely to indicate either acidity or anything of historical interest. In my area, whenever I see it I suspect acidity and antiquity and I am usually right. Not because I'm dead clever, it's just I'm a massive local/ landscape history and soil science nerd who loves figuring out what plants can tell me about former land use!
Ayot Green is a prime example of antiquity. Dotted with veteran oaks, it is a hamlet set about a triangular green; a characteristic feature in mid Hertfordshire. These tend to be of Saxon origin, probably born from piecemeal enclosure of the woods (Branch, 1970; Munby, 1977)
However Ayot Green lies immediately adjacent to the historic Brocket estate; its houses once workers cottages. The estate, which dates from at least the 1200's may once have incorporated the green. The below historic overlay map from the National Library of Scotland (2020) allows you to visualise the place as it is now and as it was in the late 1800's.
I personally think the green, with its traditional "triangle green" setup may well pre-date the estate, however the green was probably swallowed into it as meadow or wood pasture as evidenced by this photograph, collected by V. Richards on Herts Memories (2010). This shows that in the early 1900's the village was managed as meadow. Tree guards are erected around young trees, indicating livestock have access.
Similarly to many places in Hampshire's new forest, there is a distinct entrance, marked by two (now defunct) gate posts. This provides more evidence that it was enclosed for livestock. From the ornatenes of the posts I suspect it was a part of Brocket park and represented a northern entrance
If any local history buffs have any sexy sources confirming or disproving my hypothesis, do enlighten me!
The soil is underlain by the gravels, clays and sands of the Lowestoft formation For any geology fans in the audience, I've included a map and key (Edina Digimap/British Geological Society, 2020).
The Lowestoft formation produces highly acidic soils, described as "sharp and burning" by Wooldridge & Smetham (1931). On top of this they are so free draining they struggle to hold on to water or nutrients. At the same time, springs formed in the underlying clays make them prone to waterlogging.
These traits made them incredibly difficult to farm and agricultural improver Arthur Young was wonderfully vocal about it. He had the misfortune to farm these soils for nine years and his disdain for them ran through his work as an ongoing theme (Young, 1804). This provided me with much entertainment whilst I was reading his work for my MSc dissertation! I shall write a future blog about this, as my exploration of their rubbishness was fascinating stuff!
These soils were clearly something else and their presence probably explains why Brocket Park and nearby Sherrardspark wood were never lost to arable farmland.
But field woodrush doesn't like highly acidic soil does it?
Well in this part of Hertfordshire, the gravels are influenced by the underlying chalk of the Chiltern dipslope, which comes to the surface in many places, creating an interesting geological mosaic of chalk, clay and gravel. The chalk gets into the soils, creating a a buffering effect on pH that gave rise to heaths and grasslands that were......you guessed it! MODERATELY acidic!
However, arable fields were still acidic enough to require a regular dose of chalk if the pH was to be maintained at the level optimal for crop growth (around 6). Today, the control of field wood rush in lawns is best achieved by addressing pH (RHS, n.d). We can therefore predict that any soils on which it occurs has only a minimal influence from the chalk and is pretty acidic.
Where I see field wood rush in and around Welwyn Garden City, I look for encapsulated old acid grassland. Thanks to the garden city ethos of marrying town and country, the retention of field trees and open space was central to its design, which left behind an interesting relic community.
Here, I think its presence is a pretty reliable sign of both antiquity and acidity..
Branch, J.W. (1970). Hertfordshire. London, Batsford.
Biological records centre (n.d.) Field Woodrush (Luzula campestris). Available at: https://www.brc.ac.uk/plantatlas/plant/luzula-campestris
Edina Digimap/British Geological Society, (2020) Geology Digimap. Available at: http://digimap.edina.ac.uk
Herts Memories (2010). Ayot St Peter - Ayot Green. Images of Ayot Green. Available at: https://www.hertsmemories.org.uk/content/herts-history/towns-and-villages/ayot-st-peter/ayot_st_peter_-_ayot_green
National Library of Scotland (2020) Overlay maps. https://maps.nls.uk/geo/explore/#zoom=4&lat=55.78537&lon=-3.16449&layers=1&b=1
Mabbett, T (2009). Field woodrush The grass lookalike weed. Available at: https://archive.lib.msu.edu/tic/bigga/gki/article/2009nov25.pdf
Munby, L. M. (1977). The Hertfordshire Landscape. Hodder & Stoughton Ltd.
Royal Horticultural Society (n.d). Woodrush in Lawns. Available at: https://www.rhs.org.uk/advice/profile?pid=481t
Wooldridge, S. W., & Smetham, D. J. (1931). The Glacial Drifts of Essex and Hertfordshire, and Their Bearing Upon the Agricultural and Historical Geography of the Region. The Geographical Journal, 78 (3), 243-265.
Young, A (1804). General view of the Agriculture of Hertfordshire, drawn up for the consideration of the board of agriculture and international improvement. London: G & W Nicol.