When farmers were gathering their hay for stacking they needed to ensure that it was dry, or else the stack would heat up and possibly ignite.  The main content of hay, grass, dried comparatively rapidly, but other plants with more fleshy leaves dried more slowly, so it was necessary to ensure that these were also dry.  This could be done by pulling out a sample from the drying herbage and pressing it against the cheek; if it felt cold, it was still damp; if it felt warm it was dry.

It appears that the main problem was ribwort plantain (Plantago lanceolata) which is widespread and abundant in grassy areas.  In south Shropshire this was known as fire-weed, the explanation being that if it ‘was not thoroughly dried, it can cause spontaneous combustion of hay’ [1].  The name fireweed was also widely given to rosebay willowherb (Chamerion angustifolium), not because it had anything to do with haymaking, but because it ‘seems to be fond of growing on ground that has recently had a fire on it’ [2].  Other names which relate to this characteristic include blitz-weed [3] and, in Salford in the 1950s, bombsite-weed [4].

Elsewhere, in Somerset, ribwort plantain was known as fire-grass in Yarlington and fire-leaf in Muchelney [5].  In Farm Weeds: An Aid to their Recognition, published by Shell in 1952, the name fire-grass was also given to parsley-piert (Aphanes arvensis), but is difficult to imagine this plant which rarely grows more than a few centimetres high, could form a dangerous component of hay.  Perhaps as it prefers bare ground, and is soon out competed by other species in grassland, it was observed that it, like rosebay willowherb, tended to colonise and which had been made bare as a result of fire.

Fire-leaves has been recorded in Gloucestershire as a name for hoary plantain (Plantago media) [6].  This species is infrequent in hay meadows, preferring frequently mown grassland, such as churchyards, so it is possible that there was some confusion, and ribwort plantain was intended.

Another plant which could cause hay to overheat was great burnet (Sanguisorba officinalis), known as hot-weed in Brecknock and Radnor, and ‘said to cause hay to heat up if present in large amounts’ [7].

1. R. Mabey, Flora Britannica, 1996: 322.

2. Lincoln, November 1991.

3. e-mail, July 2017.

4. Oldham, Greater Manchester, December 2015.

5. A.S. Macmillan, Popular Names of Flowers,  Fruits, etc., 1922: 106.

6. G. Grigson, The Englishman’s Flora, 1987: 334.

7. Llandrindod Wells, Powys, September 1991.

Images:   main, ribwort plantain, Woolwich Common, London Borough of Greenwich, November 2019; inset, hoary plantain, All Saints churchyard, Marlow, Buckinghamshire,  October 2019.

Edited 17 March 2023.