Timothy, the Hay Fever Culprit?

Phleum pratense and Phleum bertolonii spikelets © Karen Netto (Andrews)

The UK has one of the highest world rates of hay fever in its population, rivalled only by Sweden. The summer hay fever is sheer misery for many UK residents. Between 20 and 25% of the UK population suffer. 90-95% of these annual sufferers are allergic to grass pollen. Timothy, Phleum pratense, is generally recognised as one of the main culprits.

Know your Enemy

What does this offending grass look like?

A Case of Mistaken Identity?

Phleum pratense‘s spikelet is often confused with the inflorescence of Alopecurus pratensis, Meadow Foxtail. Hower, the latter grass is one of the first to appear in spring. If you make yourself familiar with its characteristics with a hand lens at that time, you will not be deceived later in the year when Phleum pratense‘s inflorescence appears. It also has a distinctly coarser feel to the touch. I find the first two descriptions used by Dominic Price particularly memorable:

  • A microphone-like inflorescence
  • Double-awned glume with the look of Batman’s headgear or Devil’s horns under a hand lens
  • Blunt ligule
  • Flowering June to August, sometimes persisting into September
  • Spikelets can often be found as dried relics or with chewed appearance at field edges and roadsides later in the year
  • Bulbous base with shallow roots
  • Green in in winter, with tillers in both spring and autumn.

Distinction by Chromosomes

While I was working on my MSc grass project, I found the distinction between Phleum pratense, Timothy and Phleum bertolonii, Smaller Cat’s-tail, particularly confusing. As I discovered both specimens in the same patch of grass on campus, the distinction based on length of the inflorescence seemed to be more a matter of plant variation. Some botanists prefer to describe a subspecies. Cope and Gray advise that Timothy is an extremely variable species with a large number of cultivars introduced for hay or grazing. No single characteristic is considered totally reliable for identification other than the different chromosome numbers: pratense is hexaploid, 2n = 42; bertolonii diploid, 2n = 14). Thus, true species distinction becomes impossible in fieldwork.

Sole Culprit?

It should be stated in Timothy’s defence that grass allergy sufferers may be sensitive to more than one species of grass. They can be allergic to a small number or a much larger range of grasses. The other commonly mentioned culprit is Perennial Rye Grass, Lolium perenne. We can’t be sure how much of the blame should be attributed to the Smaller Cat’s-tail. According to the MetOffice, there are 150 other grasses that cause hay fever. Research is ongoing to identify and isolate the culprits for more informed pollen count warnings.

The grass hay fever season peak is between June and July when grasses release huge amounts dry, dusty pollen to reproduce. This is peak flowering season for Timothy grass. It seems extraordinary to think that Timothy’s pollen grains of between 22-122 micrometers in diameter can cause so much misery. Some poor souls are also allergic to various trees and wind-pollinated weed pollen extending the season of suffering for many more months of the year.

Hay Fever on Increase

Allergy desensitisation treatment is based on Timothy pollen, therefore the effectiveness is somewhat hit and miss. It is expected that 30 million people will suffer with hay fever by 2030. Hay fever often starts in childhood. Sometimes it eases with age, but for many it remains an annual purgatory. Figures show that an increasing number of adults are experiencing hay fever symptoms for the first time. The rise in allergic children is particularly worrisome.

The climate emergency with its hotter, drier summers is making more of the UK population susceptible to pollen allergies. Pollen counts are on the rise for both individual days and the overall number of days exceeding past limits. Summer 2018 was the worst year on record. Pollution appears to exacerbate hay fever sufferers’ symptoms in big cities. Those who suffer with allergic rhinitis are at much greater risk of developing asthma. There are currently 18 million hay fever sufferers in the UK. Hay fever can be a contributory factor in asthma deaths. There are 5.4 million people in the UK with asthma, of whom 1.1 million are children. Hay fever also has an adverse effect on children’s education and exams as they find it difficult to concentrate and sleep in summer months.

Timothy and Farmers

Hay fever sufferers may have cause to detest Timothy Grass, but farmers appreciate it as a good animal feed. It has high nutritional content and digestibility. Grasses barely grow at all when winter temperatures fall below 5ºC. Farmers grow and store grass crops to feed their livestock in the lean winter months. They either store the mown hay dry or wet as silage. Silage forms a major part of the winter diet in the UK. Therefore, much British agricultural land is devoted to its production in spring and summer months.

Timothy and Climate Change

Timothy favours a temperate climate for optimum growth. It has shallow roots and is already noted for being intolerant of trampling. Pollen counts reduce in persistent hot weather. It should also be noted that Timothy may not tolerate the extreme heat of climate change. Digestibility decreases as temperatures increase. The quality yields previously gained and sought from Timothy Grass may drop. Farmers may have to seek alternative grasses and crops for fodder.

Pet Food with Clue to Future?

Timothy Grass is also sold in pet shops for food and bedding material for the small pets. Alfalfa from legumes is available as an alternative feed. It is much richer and denser than Timothy hay. For example, it contains higher levels of protein and calcium. It is suitable for young rabbits, but not for adult rabbits.

The pet shop might therefore suggest an alternative crop for animal fodder under climate change conditions. Alfalfa, Lucerne or Medicago sativa, has been used as an animal fodder since ancient times in warmer climates.

In the meantime, we have to hope that researchers will come up with more answers for hay fever sufferers. Living in a pollen trap under the Mendip Hills, our family solution was always to hop in the car of a summer evening and head for sea air at Brean or Weston-Super-Mare. Unfortunately, that isn’t a feasible option for many city dwelling hay fever sufferers.

References and Further Reading

Ali, Runa Dr (ed.) (2020): UK hay fever warning: nothing to sneeze at. Ultimate Guide to Hay Fever. King Edward VII’s Hospital. Last accessed 20 July 2020.

AllergyUK (?): Allergy Prevalence: Useful fact and figures. Last accessed 20 July 2020

AllergyUK (2020): Statistics. Last accessed 20 July 2020.

Averis, Ben (2013): Plants and Habitats. Forestry Commission Scotland.

Cope, Tom & Gray, Alan (2009): Grasses of the British Isles. B.S.B.I Handbook No. 13. Botanical Society of the British Isles.

Eggen, Bernd (2016): Will climate change make the effects of pollen worse. Public Health Matters Blog. Gov.uk. 4 May 2016. Last accessed 20 July 2020.

Fitzpatrick, Úna & Weekes, Lynda & Wright, Mark (2016): Ireland’s Biodiversity Identification Guide to Ireland’s Grasses. 2nd Edition. National Biodiversity Data Centre. Waterford. Ireland.

Grant, Bonnie L. (2018): Timothy Grass Care: Information about Timothy Grass Growing. Gardening Know How. 4 April 2018. Last accessed 21 July 2020

Hall, Nicholas (2017): Hay fever fever. New Scientist. 30 August 2017. Last accessed 21 July 2017.

Harris, Stephen A. (2014): Grasses. Reaktion Books.

Hubbard, C. E. (1984): Grasses. A guide to their Structure, Identification, Uses and Distribution in the British Isles. Third Edition. New Edition revised by J. C. E. Hubbard. Penguin. London.

MetOffice (?): How does the weather affect hay fever? Last accessed 22 July 2020.

MetOffice (?): Pollen research to offer hope to hay fever sufferers. Last accessed 22 July 2020.

Pawankar, Ruby et al. (2011): Overview of the path-mechanisms of allergic rhinitis. Asia Pacific Allergy. 11 October 2011: 1(3): pp. 157-167

Poland, John & Clement, Eric (2009): The Vegetative Key to the British Flora. Botanical Society of the British Isles.

PollenLibrary.com (2020): Common Timothy (Phleum). Last accessed 22 July 2020.

Price, Dominic (2017): A Field Guide to Grasses, Sedges and Rushes. The Species Recovery Trust. Version 8.

Rose, Francis (1989): Colour Identification Guide to the Grasses, Sedges, Rushes and Ferns of the British Isles and north-western Europe. Penguin. Viking. London

Small Pet Select (2019): Timothy Hay vs. Alfalfa Hay for Rabbits: Which is Best? Dorothy H. Blog. 20 February 2020. Last accessed 22 July 2020.

Stace, Clive (2010): New Flora of the British Isles. Third Edition. pp.1035 & 1037

Woodland Trust (?): Timothy grass. Phleum pratense. Last accessed 21 July 2020.

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