The following eight steps provide a practical overview of preparing and operating a pumpkin kiln safely and responsibly.
Participants who wish to repurpose an existing Halloween pumpkin may skip directly to Step 3, provided the pumpkin is structurally sound and suitable for use.
Before proceeding, please review the Safety & Responsibility page. Fire, heat, and smoke require careful attention to local regulations, weather conditions, and appropriate protective measures.
These steps are intended as general guidance. Always adapt practice to your local context and conditions.
Step 1 - Choose the Right Pumpkin
A regular pumpkin used for Halloween decorations can be suitable for a pumpkiln, provided it is structurally sound and large enough for your intended use.
When selecting a pumpkin, consider the following:
Consider size. A larger pumpkin provides more kiln space, allowing for greater wood capacity and a process that is generally easier to manage and maintain over a longer period.
Match the pumpkin to your biomass. If you already have a certain type or size of wood in mind, ensure the internal cavity of the pumpkin can accommodate it comfortably.
Check structural integrity. The pumpkin should be firm, without soft spots, deep cracks, or signs of decay.
Stable base. Choose a pumpkin that sits securely and evenly on the ground.
Participants who already have a carved Halloween pumpkin may use it, provided it remains stable and suitable for safe operation.
Selecting the right pumpkin at the beginning will make the following steps more manageable and reduce unnecessary adjustments later in the process.
Remove the internal contents of the pumpkin as you would for a traditional Halloween lantern. Clear out seeds and soft flesh to create a stable internal cavity.
The pumpkin may be carved in a familiar decorative style. However, when preparing it for use as a pumpkiln, consider the following:
Keep cut-outs moderate in size. Openings for eyes and mouth should be small enough to prevent biomass and later biochar from falling out.
Provide a sufficient top opening. The pumpkin requires at least a fist-sized opening at the top to allow vapours and gases to exit during the process.
Maintain structural stability. Avoid removing excessive material that could weaken the pumpkin walls.
There are many tutorials and videos available on how to carve a Halloween pumpkin. These can be followed for general technique, with the additional considerations above.
Use caution when working with sharp knives or carving tools. Cut away from your body, work on a stable surface, and ensure good lighting.
Proper preparation at this stage supports both safety and effective kiln operation in later steps.
Before using the pumpkin as a kiln, ensure it is properly prepared for airflow and combustion.
Dry the Interior
The inside of the pumpkin should be sufficiently dry. Excess moisture can make ignition more difficult and affect the process.
Drying can be supported by:
Wiping the interior with kitchen towels
Placing newspaper inside for several hours
Using old textiles to absorb moisture
The interior does not need to be completely dry, but it should not be sopping wet or dripping.
Improve Ventilation
To ensure sufficient venting and oxygen supply, small holes (approx. 1 cm / 0.4 inches in diameter) can be drilled into the underside of the pumpkin (see photo).
These bottom openings improve airflow during operation, support a more stable and consistent burn, and provide a controlled discharge path for quenching water at the end of the process.
Use caution when drilling or creating ventilation holes. Work on a stable surface and use appropriate tools.
Before operating the pumpkiln, ensure it is placed on a stable, fireproof base.
The surface beneath the pumpkin must be resistant to heat, sparks, and embers. Suitable options include metal trays, fireproof tiles, stone slabs, or other non-combustible materials.
Support and Ventilation
If your pumpkin has ventilation holes in the underside, it must be placed on a metal screen, grill, or mesh during operation. This keeps the holes unobstructed and allows air to circulate from below.
Because hot sparks, embers, or ash may fall through these holes, the setup must include an additional fireproof layer beneath the screen.
Recommended Setup (Enhanced Safety)
For added safety, the screen can be placed over a fireproof metal dish or pan that collects falling sparks.
The metal dish may be partially filled with water to further reduce the risk of ignition from embers.
This setup offers an additional practical benefit:
At the end of the process, the dish can also be used to collect quenching water. This helps prevent uncontrolled runoff. The collected water, enriched with dissolved minerals and fine char particles, can later be used as a fertiliser.
Select clean, dry biomass for the pumpkiln. Dry kindling wood is generally well-suited because it ignites reliably and allows for stable combustion.
Do not leave the biomass inside the pumpkin for extended periods before ignition. Biomass can absorb moisture from the pumpkin walls or ambient air, which may make ignition more difficult and increase smoke formation.
Ideally, fill the pumpkin only when you are ready to begin the process and ignite the biomass within the next few minutes.
Arrange for Ventilation
When filling the pumpkin:
Keep the biomass loosely arranged.
Allow space between pieces to support airflow.
If the material is packed too tightly, oxygen supply and heat transfer will be restricted. This may lead to incomplete conversion and increased smoke.
Proper spacing supports a more stable and cleaner process.
Fire Starter
Waxed wood wool is recommended as a fire starter. The wax coating makes it hydrophobic, improving ignition reliability.
Place the waxed wood wool at the bottom of the kiln before adding the main biomass.
Alternative Biomass
Participants may also experiment with other dry, clean biomass, such as:
Walnut shells
Wood chips
Chopped straws
Lighter biomass and smaller particles may ignite more quickly but will typically burn for a shorter duration. Adjust expectations and monitoring accordingly.
Before ignition, pause and check conditions once again.
Ensure that:
The pumpkiln is positioned on a stable, fireproof base
Ventilation holes and top opening are unobstructed
Weather conditions are suitable (no strong wind)
Water or other extinguishing means are readily available
Safety should always determine whether ignition proceeds.
Lighting the Pumpkiln
Ignition can be carried out using a long match or an extended lighter, inserted carefully through one of the carved cut-outs.
Light the fire starter (e.g., waxed wood wool) at the bottom of the kiln. Avoid placing hands directly above the top opening during ignition.
Once lit, allow the fire to establish gradually. Do not add additional biomass at this stage unless necessary.
Once ignition is established, remain present and attentive throughout the process.
The pumpkiln should never be left unattended. Observe flame behaviour, smoke levels, and airflow regularly.
As the biomass begins to convert, additional dry material may be added through the top opening if needed.
Maintain a Stable Burn
Add small amounts at a time and avoid overfilling. Keep the biomass loosely arranged to maintain airflow and prevent excessive smoke.
If smoke increases or the flame becomes unstable, check that:
The material is dry
The biomass is not packed too tightly
Ventilation holes remain unobstructed
A steady, controlled burn is preferable to a large or erratic flame.
Heat Use
The heat produced may be used in a controlled and safe manner, for example:
Roasting marshmallows
Baking bread on a stick
Preparing a simple s’more
Food preparation should remain secondary to safe kiln operation.
When the biomass has largely converted and visible flames decrease, carefully begin quenching the process by adding water through the top opening.
Pour slowly and in controlled amounts. Stand back and avoid leaning over the kiln. Steam will form immediately when water contacts hot material and can rise quickly.
If the pumpkin has bottom ventilation holes, hot water may drain from the underside during quenching. Ensure the pumpkiln is positioned on a fireproof surface and, ideally, over a metal dish or tray to collect runoff and prevent uncontrolled flow.
If the pumpkin does not have bottom holes, water will most likely exit through the carved facial openings (typically the mouth). Be prepared for this runoff and ensure that the surrounding surface can safely handle hot water, especially at the beginning of quenching.
Continue adding water gradually until all active combustion has stopped.
Once the biochar has fully cooled and dried (if necessary), it can be prepared for use.
Biochar
Biochar may be used as a soil improver in gardens or mixed in small quantities into potting soil. It can also support composting processes by improving aeration and helping retain nutrients.
Before application, biochar should be appropriately prepared (e.g., combined with compost or nutrients) according to best practice.
Quenching Water
The water used for quenching may contain dissolved minerals and fine char particles. It can be reused as a fertilising input.
Be aware that the water will typically be alkaline. Use cautiously and dilute if necessary, particularly for pH-sensitive plants.
The Used Pumpkin (Pumpkiln)
If the pumpkin remains structurally intact, it may be reused for another burn. Once no longer usable, the pumpkin remnants can be composted or disposed of as green (kitchen) waste in accordance with local regulations.
The used pumpkin should not be fed to animals.