If there are obvious patches of grass that differ in colour, texture or height to surrounding fine turf, then you probably have coarse grass in your lawn. Identifying the type of coarse grass you have isn't essential, but it might help you decide if you want to keep or remove it and, if you chose to remove it, how best to do so. The descriptions and images below will help you identify three of the most common coarse grasses:  

Annual meadow grass (Poa annua) is a very common, native coarse grass. Its leaves grow out horizontally from a central point, reaching a spread of about 20cm (8in). They are usually light green, but there are also forms with dark purple leaves. Branching flower spikes that form a roughly triangular outline have pale green flowers at the tips. These can appear at any time of year. Its seed is oval, light brown and about 2mm long.  

Depending on growing conditions, it can be annual, ephemeral (completing its life cycle in less than one year), or occasionally perennial. It has shallow, fibrous roots and can reach a height of 30cm (12in), but is generally much shorter in regularly mown lawns.
 

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

rhizomes

Many coarse grasses, such as the three above, are native to the UK and are great plants for wildlife, particularly butterflies. Coarse grasses are great additions to wildflower meadows, adding height with their swishing seedheads. Even when allowed to grow in a regularly mown domestic lawn, coarse grasses help increase its biodiversity: 

• Caterpillars of gatekeeper butterflies feed on annual meadow grass and couch grass. 
• Caterpillars of speckled wood butterflies enjoy couch grass and Yorkshire fog.  
• Caterpillars of the small skipper butterfly and wall brown butterfly also feed on Yorkshire fog.  
• Garden birds feed on the seeds of coarse grasses. Annual meadow grass is particularly valuable as a source of winter food for finches. 

© Shutterstock

A gatekeeper butterfly

© Shutterstock

A small skipper butterfly

Here are our answers to your most common questions about dealing with coarse grasses in lawns:    

How invasive are coarse grasses?  

Coarse grasses use a few methods to increase their spread. Annual meadow grass quickly colonises bare patches of fertile soil by seed. Its success in lawns is due to its ability to flower and seed, below the height of mower blades, year-round. Wind, water, animals or human activity can spread the seed.  

Some coarse grasses, such as Yorkshire fog, also spread by runners (rooting stems) that grow outwards from the main clump. If these grow over bare soil, or into an area where fine grass species are weak or sparse, they will send down roots, increasing the size of the clump.  

Unlike the others, couch grass spreads primarily by rhizomes (underground stems) and can regenerate from small sections of rhizome. It is less likely to spread by seed. See our page on couch grass for more details.  

Do I need to get rid of coarse grasses in lawns?    

No – allowing course grasses to grow in your lawn is a great way to boost the biodiversity of your garden. As they look green and can be walked on, played on and mown along with traditional lawn species, there is no need to remove them from your sward. They are particularly attractive, and more beneficial to wildlife, if allowed to grow tall and set seed, so there is no need to remove them from wildflower meadows or species-rich lawns either. 

You will only need to get rid of course grasses if you want an immaculate, less biodiverse, fine lawn.

Coarse grasses add interest to meadows and species-rich lawns 

What is the easiest way to kill coarse grasses?    

If you have coarse grasses growing in your lawn and they cannot be tolerated, there are methods of controlling them:  

• Improve the health of your lawn – coarse grasses are less able to establish in dense, healthy lawns. Follow a programme of lawn maintenance in spring/summer and autumn to boost the vigour of your lawn. If patches of your lawn are struggling, overseed with a mix to suit the growing conditions.  
• Mow regularly – this will prevent some of the taller coarse grasses flowering and setting seed. Fine grasses are better adapted to tolerate regular cutting, whereas it will weaken coarse grasses. Use a collection box to remove the clippings, which may include coarse grass seed.  
• Avoid frequent watering – watering little and often during dry spells benefits coarse grasses, like annual meadow grass, that have shallow root systems. As lawn grasses are generally drought tolerant, there is no need to water an established lawn; even if it becomes brown during hot, dry weather, it will usually recover following a decent amount of rain. 
• Fork out plants – insert a hand fork under the main clump or rooted sections of stem and lift out the roots. This is a good, easy option for quick results on small areas of lawn. September is a good month to remove coarse grasses by hand, as it will reduce the population before winter (a season when they can thrive) and you can re-seed patches of bare soil straight away.    

Should I use weedkiller?   

No – selective lawn weedkillers are not effective on coarse grasses and non-selective weedkillers will kill all grass species, including those you wish to grow. As non-chemical control methods are effective, even if time-consuming on large lawns, there is no need to use a weedkiller.  

For more information, see our page on Weeds: non-chemical controls.