A Profile on the Grass and Weeds that cause Hay Fever

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Summer isn’t over yet!

That’s right. The weather may be up and down but there are still two more months of pollinated air swirling through our late summer breeze. Trees release pollen in March to early May, grasses release their pollen from late May to early August, whilst weeds and certain shrubs release their pollen in late summer.

Seeing as 95% of hay fever sufferers are allergic to grass pollen we thought we’d familiarise ourselves with the grasses and weeds that cause so much sniffling and sneezing during our mid-summer barbeques!

 Which grasses are the main culprits?

Although it does depend on what country you live in, and which season of the year we are in, perennial rye and timothy grass are the main culprits for those that live in Britain.

Perrenial Rye (Lolium perenne)
Perrenial Rye (Lolium perenne)

Perennial Rye is a grass from the family Poaceae. It is native to Europe, Asia and northern Africa, but is widely cultivated and naturalised around the world.

Perennial Rye-grass is a harsh coarse grass, with green stems and narrow, blade-like leaves.

It grows in clumps and can be found on roadside verges, rough pastures and waste grounds, and is often used around homes, schools, and parks. It prefers full sun but will tolerate partial shade. It was once the most commonly sown grass in leys (fields used for grazing livestock) and is now often used for reseeding grasslands.

It flowers from May through summer and can vary from being an annual to very persistent year after year.

Did you know?

Selected seed mixes are used extensively for sports pitches, especially winter sports, in temperate climates, because of its wear resistance and its ability to regenerate.

Timothy-grass (Phleum pretense)
Timothy-grass (Phleum pretense)

Timothy Grass is an abundant perennial grass native to most of Europe except for the Mediterranean region. Since its introduction to the USA in the early 18th century it has been one of the most common grasses in New York too. It is also known simply as timothy, or as meadow cat’s-tail or common cat’s tail.

The grass has flat leaves and grows two to four feet tall. The leaves are hairless, rolled rather than folded, and the lower sheaths turn dark brown. The distinctive flowerhead is up to 6 inches long and purple in colour.

Timothy is one of the most prevalent grasses in the world, and grows most effectively in cool, humid climates. It is most commonly used as feeds for horses and grass for lawns.

The flower of Timothy grass starts to grow in June, while the flower pollinates towards September. The wind carries the pollens away from the flowers and it continues to linger on the environment until late summer. This is when the most allergies are triggered. More pollen is carried into the air during hot and windy days, which is why most allergic reactions occur during late summer and autumn.

Did you know?

Timothy Grass was first called “hurd grass”, named after its first description by American settler John Hurd. But a farmer named Timothy Hanson began to promote cultivation of it as hay in the 1720s, and the grass has been known by its present name since then.

Mugwort (Artemisia vulgaris)
Mugwort (Artemisia vulgaris)

Mugwort is a hardy perennial plant that is native to Europe and Asia but now is also present as a weed in North America (especially the eastern states). Mugwort is part of the Asteraceae family that also includes: daisies, sunflowers, dandelions, and ragweed.

It can grow up to 6ft high, is reddish-brown in color, and prefers full or partial sun in moist to dry soils. Mugwort can be found growing wild along streams, on rocky soil, and in rough terrain.

Mugwort pollen is a very allergenic weed pollen and common cause of hay fever. The pollen generally travels less than 2,000 meters, and the highest concentration of mugwort pollen is generally found between 9 and 11 am.

Did you know?

Mugwort has been used for decades by various cultures for medicinal purposes such as treating vomiting, irregular menstrual cycles, anxiety, epilepsy, stomach ulcers, malaria and cancer.

Sheep Sorrel (Rumex acetosella)


Sheep Sorrel and its subspecies are common perennial weeds, also known as red sorrel, sour weed, and field sorrel.  The plant is native to Eurasia and the British Isles,‪ but it has been introduced to most of the rest of the northern hemisphere.

Sorrel has a slender and reddish upright stem that is branched at the top, reaching a height of 18 inches. The green arrow-shaped leaves are small, slightly longer than 1 inch, and smooth with a pair of horizontal lobes at the base. Both the ridged stems and female flowers are a deep red.

It is commonly found on acidic, sandy soils in heaths and grassland, or disturbed areas such as abandoned mining sites.

Sheep Sorrel blooms during March to November, and pollination occurs from May through September, depending on the latitude. The pollen can travel great distances, and is considered a moderate allergen. One study determined that a single Sheep Sorrel flower can produce up to 65,000 pollen grains, with a single plant producing over 4 million grains!

Did you know?

Sheep sorrel can be quite tasty too, despite its fondness for the acidic. Use it’s lemony tangy leaves as a garnish, a tart flavoring agent, a salad green, or a curdling agent for cheese.

English plantain (Plantago lanceolata)
English plantain (Plantago lanceolata)

 Also known as narrowleaf plantain, ribwort plantain,‪ ribleaf, buckhorn plantain, buckhorn, and lamb’s tongue, this is a common weed of cultivated land. Native to Europe and Asia, but now grown practically anywhere in the world, the English Plantain is common in most temperate regions, and is considered a troublesome pollen weed in such diverse areas as New Zealand, Mauritania, Italy, Canada, Ecuador, Belgium, Germany, France and the USA.

This is a green weedy plant with a rosette of basal leaves and flowers on a leafless silky stem. The dark green leaves at the base of the stalk are oblong or lance-shaped with leaf axils that are often filled with long brownish cottony hairs.

Plantain is found on grasslands, roadsides, and cultivated ground. This plant prefers highly disturbed areas and is a troublesome weed; it often invades lawns and gardens.

The plant flowers from April to August. English Plantain produces more pollen than the other Plantains, and is the second most important cause of allergy, after grass pollen allergy, in those that suffer from hay fever.

Did you know?

English Plantain is used frequently in herbal remedies. A tea from the leaves is used as a highly effective cough medicine.

Kentucky Bluegrass (Poa pratensis)
Kentucky Bluegrass (Poa pratensis)

 Also known as smooth meadow-grass or common meadow-grass, this is a perennial species of grass native to Europe, Asia, North America, and northern Africa.

The Kentucky Bluegrass is a dark-green, medium-textured turf, with broad stiff-looking leaves that have a boat-shaped tip that are smooth or just slightly roughened. The name Kentucky Bluegrass derives from its flower heads, which are blue when the plant is allowed to grow to its natural height of two to three feet.

Kentucky Bluegrass is a valuable pasture plant, characteristic of well-drained fertile soil. It is also used for making lawns in parks and gardens and is common in cool moist climates.

It flowers from May to July, and is one of the most serious hayfever grasses in northern areas of the U.S, producing more pollen than any other grass. However it only makes pollen when it blooms, so if the grass is kept mowed then it wont flower.  In Bluegrass that isn’t mowed, tiny clusters of flowers rise above the grass blades. Each day, almost like clockwork, some of the flowers open and release their pollen into the air. The process happens at the same time every day until all the flowers in the spike have opened up and shed their pollen.

Did you know?

Bluegrass isn’t actually from Kentucky. It came from Europe with the first settlers to North America. They planted the grass in pastures to feed their livestock because it was nutritious, fast growing, and able to stand up to heavy grazers. Soon it spread to meadows and open woods. As communities grew, people planted bluegrass around their houses.

Fat Hen (Chenopodium album)
Fat Hen (Chenopodium album)


 This is a fast-growing weedy plant also known as lamb’s quarters, melde, goosefoot and pigweed. Its native range is obscure due to extensive cultivation,‪ but includes most of Europe, Africa, Australasia,‪ North America,‪ and Oceania.

Fat Hen tends to grow upright at first, reaching heights of 3 meters, but typically becomes recumbent after flowering (due to the weight of the foliage and seeds) unless supported by other plants. The alternate leaves are diamond in shape, with a waxy coat, and have a whitish coat on the underside.

The plant is cultivated as a grain or vegetable crop as well as animal feed in Asia‪ and Africa, whereas in Europe and North America, it is commonly regarded as a weed in places such as potato fields. It in fact is so robust and competitive a weed it causes great crop loss for many farmers. It thrives in disturbed rich mist soils and can be found in yards, roadsides, and waste places as well as farms and gardens.

The tiny green wind-pollinated flowers bloom between June and October.

Did you know?

The scientific name Chenopodium comes from Greek words ‘chen’ and ‘podion’ meaning goose and small foot. Hence the name!

If you’re heading to America this summer look out for….

The Sagebrush
The Sagebrush

Bermuda Grass (a native to African, though watch out for its seeds being sold for lawn grass in the UK too!)

Bermuda Grass
Bermuda Grass

 and Ragweed, which has started making it’s way to the UK!


Check local pollen counts before arranging outdoor activities

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