Join the Oak Apple Harvest

Marble Oak Gall
Knopper oak gall - photo by Matt Larsen-Daw

Knopper oak gall – photo by Matt Larsen-Daw

We need your help to make history! We are calling for people across the UK to harvest oak galls to create the ink that will be used to write the final Tree Charter, harking back to the ink that was used for documents such as the Magna Carta and the Charter of the Forest.

Oak apples are a familiar site across the UK – intriguing woody spheres nestled among the leaves of oak trees. Despite their appearance and this colloquial name they are not actually fruits, but growths that have built up around the eggs of certain kind of gall wasps. They have long been surrounded by folklore and tradition, and in the past even inspired an annual national holiday on 29th May. The round ‘oak apple’ galls are in fact just one of a range of different galls that result from different wasps and appear on different species of oak. Some, such as the knopper oak gall, distort acorns into strange alien shapes – and in doing so prevent that acorn from becoming a viable seed.

Despite not being fruits, oak galls have been a useful harvest for people throughout history. From the 5th to the 20th Century – oak galls were crushed to create  ink that was used to pen some of the most important documents in the nation’s history. Although in recent years it has been replaced by chemically produced inks that can be made in bulk in a variety of colours, this traditional method of making ink from a byproduct of a natural process is still revisited by artists today.

Artwork by Jo Lathwood

Artwork by Jo Lathwood

The ink for the Tree Charter will be made by artist Jo Lathwood. The information and images below are taken from Jo Lathwood’s leaflet ‘Oak Gall Ink: A short history and recipe’ which can be found and purchased on her website.

There are over 200 types of oak galls in the UK. Oak galls are formed when parasitic wasps lay larvae onto an oak tree. The gall, which is the wasp’s cocoon, is not produced by the wasp, but provided by the host, in this case an oak tree. Therefore the elements of the gall are similar to that of the tree, not the wasp. They have been used throughout history as materials for dye, ink and even medicine. When the wasp is fully formed, it burrows its way out of the gall. That is why oak galls  often have small holes in them.


There are many different recipes for making oak gall ink, but most use very similar ingredients and a similar technique. Jo’s process is time-consuming, and involves boiling the galls, adding salt and bicarbonate, and leaving the mixture for a week (for the full recipe, visit Jo’s website).

The final Tree Charter will be written in this special Oak Gall Ink, and you can play a part in creating this piece of history. Harvest oak galls over the coming weeks and send them in to the Woodland Trust before 31st August 2017.


A quick guide to taking part in the Oak Gall Harvest

  1. Check the oak trees you pass for oak galls (handy guide below).
  2. Before picking the galls check that there is an exit hole, otherwise the wasp larva will still be inside. If you can’t see one, come back to that tree after a week or so to check again.
  3. Pick the galls carefully to avoid damaging the tree. If it is an acorn gall it is fine to remove the whole acorn.
  4. Put the galls in a jiffy bag or strong envelope and send it to: The Tree Charter Team, The Woodland Trust, Kempton Way, Grantham, Lincolnshire NG31 6LL
  5. Please include a note with your name, email and details of where the oak galls were found. Please ensure you send them in before the end of August 2017.

A guide to oak galls by Jo Lathwood

If you have any questions please email

Trees are vital sources of food and habitat for a huge range of wildlife.

Help ensure we have thriving habitats for diverse species in the future.
Show your support for woods and trees: Sign the Tree Charter today




Cover photo: Marble oak galls from Turkey Oak in a Hampton, London. Photo: Matt Larsen-Daw

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