Bracken Health and Safety Information

Ptaquiloside,a carcinogenic chemical is found in both the bracken fern and its spores. It has been shown that the spores can cause cancer in mice and bracken has been linked to bladder and intestinal cancer in cattle and horses as well as a number of diseases in other farm animals.  It has also linked to human gastric cancer where people, particularly children, eat dairy products where bracken has formed a significant part of the cows diet. In some cultures bracken has been used as a food for humans being eaten  fresh, or preserved, in making  bread,  brewing beer, and the starch from rhizomes used  to make  flour and  confectionary.  It has been implicated in human bladder esophageal and stomach cancers.

 In health and safety terms while bracken may be a hazard to humans there does not appear to be any firm evidence, yet, that it presents a significant risk to humans. However, it is better to take reasonable precautions. Physical contact with bracken during harvesting, heaping and turning should be minimised, particularly in late August - October when it may be sporing.    However, the Forestry Commission has, due to conservation restrictions, cut and composted bracken in September and later in the year when it is lignified and drying out.   An advantage of a September cut is that there is low or negligible Ptaquiloside present. 

One of the factors that reduce the risk of ingesting the spores is that bracken only spores at intervals of about ten years.  The spores are found in a thin strip on the curled-over edge of the underside of   the fronds but do not usually extend to the extreme tip of the leaflet. 

Gloves and a facemask should be worn when handling the plant. The use of gloves to protect the hands is a sensible precaution at any time of year as pulling up bracken stems by hand can result in cuts.

Bracken may also harbour sheep ticks, which may, carry Lime Disease, so it is sensible to check exposed areas of skin after working with bracken

Bracken spread and control

Bracken (Pteridium aquilinum) is a native British fern growing, also found across the world, which grows in both acid and neutral soils in open situations and woodlands. Bracken can reach over 1.5m (5ft) in height it is the only fern that has side branches. In late summer, bracken fronds turn first a golden colour and then brown dying   back to ground level in the autumn and over-winter in this state.  New growth develops from the base in spring.

Bracken spreads by both underground stems rhizomes and spores that are carried by the wind. Bracken has high potassium content.

 It used to be cut in the autumn to be used as animal bedding, in tanning, soap and glass making, as a fertiliser (bracken ash), and as a mulch or compost.

It is also cut to restrict spread and cutting while green can be very effective in will eventually eradicate the bracken.  This is also provides a supply of bracken that can be utilised to make compost.

Composting Bracken

As mentioned above bracken was traditionally used as mulch. The brown autumn and winter fronds can be rotted down in a plastic sack in the same way as autumn leaves are allowed to decompose over two years to make leaf mould.

However, one of the advantages of composting bracken over using it as a mulch   is that it improves the water retention by increasing the proportion of particles of less  than 6 mm in length  (known as ‘fines’).

 A higher proportion of fines areobtained if the bracken is cut while green rather whenit isolder and has started to turn in the autumn. In addition to the time of year the size of the fibres in the bracken, also depend on how it is cut.  On a commercial scale using forage harvester, double chopping produces more finely divided material than single chopping. Similarly, at the home composting scale shredding before adding to the compost bin produces smaller material than cutting using Secateurs. 

Cold Composting Bracken

Recycle Now list bracken as one of the greens that can be used in home composting. Fronds can be composted as bracken spores (which might be present) seldom seem to germinate and grow in the compost heap or following composting but small sections of the roots can regenerate, and therefore should not be used when cold composting.

 The young green bracken fronds can be composted on their own or added to an existing mixed  cold compost bin or heap and will decompose slowly, enriching the nutrient content of the compost. It is not necessary to shred these young plants but doing so does speed the composting process. Bracken stems being woody are not suitable for composting where a quick turn round is required unless they are first shredded or chopped. If planning to cold compost bracken the brown winter bracken is relatively easy to harvest and   is free from ptaquiloside it is best composted separately as if making leaf mould. 

Hot Composting Bracken

I would recommend that bracken is hot composted with a target temperature of 60C for several weeks as the heat destroys the allelopathic chemicals, produced by bracken,  that restrict the growth of other plants. (Not a feature welcomed in compost) and also breaks down the carcinogenic ptaquiloside.  At lower temperatures, it may take about 5 months to achieve this result.   The addition of cow or horse manure makes an effective activator and if sufficient bracken is cut to warrant a separate heap or bin the manure   can be mixed of ratio of 4:1.to help achieve the required temperature.

The Forestry Commission have composted bracken on a larger scale (using ten-metre long bays).  I include details here for the benefit of those who have a paddock or wooded area being invaded by bracken.  Water was added to the bracken to give minimum moisture content of 70% fresh weight. Up to 40 cu metres of bracken was composted in bays filled to a height of 1.5-2 m. The material was   turned to prevent compaction and to maintain a working temperature in the region of 55-60ºC.

 During composting the pH of the bracken increased from acid (pH 5.5-5.8) to neutral (pH 6.5-7.0). If acidic compost is preferred the researchers showed that the addition fertilizers such ammonium sulphate prevented the rise in pH. Allowing the bracken compost to mature also resulted in a degree of reacidification.

Bracken has also been successfully composted in windrows using manure to give the 4:1 ratio used above.  The initial moisture content should be 70% windrows should be turned regularly, when the temperature of the material reaches 60-70C, to aerate the material facilitate the composting process.

An alternative bracken compost mix uses shredded bracken, farmyard manure and bark

As an additional safety precaution it is recommended that the compost should stored in a to maturation bin until the year following harvest to ensure that any carcinogens present in the bracken are broken down. It might be advisable to consider allowing compost made by cold composting to mature for a longer period and it is suggested that the maturation stage is prolonged for at least a full year after the composting process has completed.

Composting Bracken Further Information

Further reading

(Should we be frightened of bracken? A review of the evidence https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1756650/pdf/v052p00812.pdf)

Photographs of the plant in various stages, including sporing http://wildflowerfinder.org.uk/Flowers/B/Bracken/Bracken.htm).

http://www.forestry.gov.uk/pdf/fcin3.pdf/$file/fcin3.pdf

http://www.allotment-garden.org/gardening

Commercial system at http://www.gowercommons.org.uk/compost/