Oak Galls Explained: From Nature to Practical Uses
- Astrid van Essen
- Jun 5
- 4 min read
I first heard of oak galls—also called gall apples—during a natural dyeing course. They were mentioned as a rich source of tannins, applicable for both ink and mordanting fabric. At the time, I hadn’t seen one in real life. But I recently moved house and started exploring the nearby woods, and I suddenly noticed these strange little spheres on leaves and branches of an oak tree.
Once I realised what they were, I was fascinated. What looked like something diseased or odd was a miniature world of insect activity—and a powerful natural material with deep roots in herbal and craft traditions.
In this post, I’ll explain oak galls, how they form, and how they can be used for everything from natural dyes to historical ink.
What Are Oak Galls?
Oak galls are knobbly, sometimes marble-like growths on oak trees when tiny gall wasps lay their eggs in the tree’s tissues. The oak responds by growing a protective shell around the larva, creating a gall. It's a clever little ecosystem: the wasp gets a home and food source, and we get an unexpected herbal and crafting ally.
There are several types, but the most common include:
Marble galls – round and hard, often found on twigs
Oak apple galls – larger, spongier, often found on leaves
Spangle galls – flat and disc-like, usually on leaf undersides
Knopper galls – irregular, lumpy growths that distort acorns
Despite their alien look, galls don’t usually harm mature trees.
When to Look for Oak Galls
You’re most likely to spot mature oak galls from late summer into autumn, when they fall to the ground. They can appear earlier but are best picked when fully formed and dry. Not all oak trees have them yearly—it depends on local gall wasp activity and species.
Look for:
Firm, dry galls with tiny exit holes (a sign the wasp has left)
Fallen galls under English oak or sessile oak
Galls that feel solid and show no signs of mould or softness
🍂 Tip: Bring a small basket or paper bag to collect your finds—they store well if kept dry.
What’s Inside an Oak Gall?
Inside a gall is a dense core of plant tissue, sometimes called the pith. This surrounds a central chamber where the wasp larva once lived. The interior of marble galls is woody and solid. Oak apples have a lighter, spongier texture.
The whole gall—shell and pith are rich in tannins, making it incredibly useful for dyeing, ink, and traditional herbal use.
Uses for Oak Galls
1. Iron Gall Ink
Oak galls were historically used to make iron gall ink—a deep, rich black ink used for centuries in manuscripts, drawings, and legal documents.
You only need:
Crushed oak galls
Rusty iron or iron sulphate
Water and gum arabic (for binding)
It’s simple, alchemical, and surprisingly effective.
Oak Gall Ink Recipe
Traditional Iron Gall Ink for Writing & Art
👉 Access the digital version of the recipe here: Oak Gall Ink
You will need:
4–5 dried oak galls
½ tsp iron sulphate (or a few rusty nails)
½ cup (120 ml) warm water
½ tsp gum arabic (optional – helps ink flow and bind)
Glass jar with lid
Mortar & pestle or hammer (for crushing)
Fine mesh strainer or muslin cloth
Instructions:
Crush the galls using a pestle and mortar (or place in a cloth and gently hammer).
Add crushed galls to your jar and pour over warm water. Let steep for 24–48 hours.
Strain the liquid into a clean jar to remove debris.
Add iron sulphate (or drop in rusty nails). Stir gently. As the tannins react, the ink will darken to black.
Mix in gum arabic to thicken and preserve.
Store in a sealed glass jar. Shake gently before use.
Tip: Ink gets darker with time. For best results, use with a dip pen or brush.
2. Natural Dyeing & Mordanting
If you’re into plant dyeing, oak galls are one of the best natural tannin sources. You can:
Use them as a mordant to help plant dyes stick to fabric
Steep them to create earthy greys and browns
Combine with iron to shift colours towards cool charcoal tones
You’ll need to crush or grind the dried galls and soak them to release the tannins.
3. Traditional Herbal Use
Oak galls were once used in herbal remedies for their astringent and antibacterial properties. Powdered gall was used on wounds, sore gums, or inflamed skin.
Always consult a qualified herbalist before using medicinally. High tannin content means they’re potent and can irritate if overused.
Are Oak Galls Safe?
Yes, for handling and crafting. The wasp inside doesn’t sting people and is long gone when galls fall. The galls themselves are just modified plant tissue.
Trees also tolerate them well. While a heavy gall year can stress young saplings, mature trees usually carry on unaffected.
Foraging Responsibly
Like all natural foraging:
Only take what you’ll use
Leave some for wildlife and biodiversity
Don’t pick unripe galls that are still growing on the tree
Store them dry and whole until needed
Final Thoughts
Oak galls are wild things you might walk past a hundred times before noticing. But once you know what they are and what they can do, they open a door to centuries of craft, herbalism, and nature-based creativity. Whether you’re into ink, dye, or enjoy the quiet pleasure of foraging with a basket in hand, oak galls are worth getting to know.
FAQ
1. What exactly are oak galls made of? They’re made of plant tissue, formed by the oak tree in response to gall wasp activity. Inside is a central chamber where the wasp larva once grew.
2. Do all oak trees have them? No—it depends on the species and whether gall wasps are active nearby. English and sessile oaks are most commonly affected.
3. Is the inside (pith) useful? Yes! The whole gall, including the pith, is rich in tannins—ideal for ink and dye projects.
4. Can I use fallen galls? Yes, but ensure they’re dry, firm, and not mouldy. Look for tiny exit holes showing the wasp has already emerged.
5. Is it safe to use oak galls in herbal remedies? Traditionally, yes, but tannins are strong. Use only under guidance from a qualified herbalist.
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