Horse Mushroom UK

Big Bonus – The Horse Mushroom

Right now there are quite a few Agaricus (mushroom) species. I have already seen many species in varying urban habitats. I was especially lucky when I stumbled across these beauties literally round the corner from my house on a large grassy verge.

Horse Mushrooms in grassThe most welcome Horse Mushroom (Agaricus arvensis) is a great tasty mushroom that grows in most types of grassland, mainly permanent pasture land, but to reiterate, in this case it was a small grassy front lawn/verge.

They’re often found growing in large rings and this was no exception, even though it was only a partial ring. Still plenty to go around though.

The word ‘Horse’ used in the English name doesn’t reflect on where they can be found, such as fields with horses in (which is a common misconception) but is in reference to their large size. The largest in this group was 15cm across, the size of a small plate. 20cm is the maximum size on average and even at these dimensions, they are still relatively fresh and ready for the pan. If you find what appears to be a Horse Mushroom, but has a 30cm diametre cap, then you’ve probably found a Macro Mushroom (Agaricus urinascens), very similar indeed to our Horse Mushroom but slightly more scalier on the cap. That’s another story for another time.

People often avoid the Horse Mushroom because of the yellow (pale ochre) colouring that appears on the cap as it ages. Some are unsure that they could be dealing with the rather unwelcome ‘Yellow Stainer’, an extremely common look alike that could cause nasty gastro upsets (read all the about the Yellow Stainer in this post). In fact, some Agariucus xanthodermus were quite happily growing on a grassy verge nearby that very day!

But have no fear, the Horse Mushroom has some key characteristics that set it apart from the rest. Initially I always do the ‘Yellow Stainer’ test in which I rub the side of the cap and get the base of the stem out of the ground and snap it in half. If there’s some ‘strong’ chrome yellow colouring I simply avoid it. The Horse Mushroom has no extreme colouring like this and no colouring at all in the base of the stem flesh.

If you look around and find a very young example, the gills will be veiled by the what is to become the ‘ring’ on the stem (see picture below). A distinctive jaggedy ‘cogwheel’ pattern runs around the outer circumference of the membrane. This is always a good sign.

The young gills are white at first and turn pink, then eventually chocolate brown as time goes by. I found these at a good time and I didn’t hesitate at all in collecting some for my tea, leaving a few to do their thing.

They eventually ended up in a lovely mushroom soup (if I don’t mind saying so myself). I hope you too have some good luck in finding these beautiful and tasty mushrooms. Enjoy.

Horse mushroom pictures

The Horse Mushroom can grow up to 20cm in diametre. Notice the ‘cogwheel’ pattern on the veil, covering the gills of the younger mushroom (bottom left).



5 – 20 cm across. Initially domed cap expanding out. Creamy white, yellowing with age. Flesh firm and thick. Slight smell of aniseed (more so when young). Veil on underside initially covers gills. Has a ‘cogwheel’ pattern.


8-10cm x 2-3cm. Same colour as cap. Often becomes hollow.


Free from stem apex. White at first, then pink, then chocolate brown with age.
Spore Print: Dark purple brown (see how to take a spore print here).


Grassy pastures, lawns and sometimes grassy verges. Often in rings. Late summer – autumn. Common.


Edible and excellent. Good mushroomy flavour.

The Genus AGARICUS (Wood Mushrooms/Mushrooms): Characteristics to look out for:

• Many discolour yellowish, reddish or pinkish when cut or bruised.
• Those that discolour bright/chrome yellow should be avoided for consumption.
• Gills in young specimens are often pink (white in a few) – maturing darker brown.
• Make note of any smells, such as aniseed or a typical strong ‘supermarket’ mushroom smell.

7 replies
  1. Mushroom Mike
    Mushroom Mike says:

    I do the same ‘Yellow Stainer Test’ but I also smell the bottom of the stem as well. If it smells of Dettol or TCP that is another key indicator. Also watch out for Agaricus moelleri, though you shouldn’t mistake that for a Horse Mushroom.

    • J C Harris
      J C Harris says:

      Good tip about the smell. It isn’t a nice smell to get off a mushroom is it? And as you say Agaricus moelleri (Inky Mushroom) has similar yellow bruising but the cap is covered in fine grey/brown scales and it’s habitat is woodland only, so not much chance of mistaken ID. Very good point though.

  2. Kevin Breegan
    Kevin Breegan says:

    Picked a Horse mushroom yesterday and fried it in butter> Had on a barn cake with sausage and it was absolutely delicious. So I went back today to pick a basket full ready to make some lovely soup. As soon as I started cooking them, however, they went very yellow so I threw them all away. When picking the first one and also when preparing the large batch I did the rubbing test and cutting the base of the stem without any yellowing occurring. I had no adverse effects from the one I ate and enjoyed.
    Another observation was that when the batch for the soup cooled down they went back to their original colouring, but I thought better to be safe than sorry

    • J C Harris
      J C Harris says:

      Smart decision there Kevin. Was there an phenol/inky smell to them? They must be Yellow Stainers if they had that smell. Another note is that I have found Yellow Stainers and Horse Mushrooms growing close to each other!

    • Anne Young
      Anne Young says:

      The same happened to me yesterday. I was cooking some young horse mushrooms and they initially went slightly yellow. I continued and the yellow disappeared. We ate them all in an omelette. Delicious. No after effects!

  3. Dr Eric C O’Brien
    Dr Eric C O’Brien says:

    On Oct 20 at Portmarnock Golf Club , Ireland I picked areal good looking Horse Mushroom .
    Ate it that eve — fried in a pasta sauce .
    Next morning I was deadly ill – developed Acute Renal Failure .
    Am on outpatient Dialysis at present hoping to make a full recovery .
    Dr Eric C O’Brien. [age 81]


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  1. […] stark, chrome yellow staining as I scored the flesh, so they weren’t Yellow Stainers either. Horse Mushrooms […]

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