Aging wood with a UV sterilizer? Trying to get the right color before locking it in

I do not like white deadwood for most bonsai, the kind you get with lime sulfur treatments. I’d rather see the colors we find in nature. Now then, like all things bonsai, the question is: How to replicate decades or centuries in a short amount of time?

One approach I’d like to take is artificial UV aging of the deadwood. I’ve only done a small (thus dangerous) amount of research. The most powerful approach I can find is a 36W UVC aquarium sterilizer.

UVA and UVB spectrum light is what we deal with on planet Earth. UVC is blocked by the atmosphere. Lucky for us, because UVC is the most dangerous type. That’s why aquarium equipment would use it to kill microbes. Will it work for aging wood? I have no idea.

Here’s what I’ve found and what I plan to do:
SAFETY FIRST: As mentioned above, UVA-B-C are dangerous light sources to experiment with. Anything designed to kill microbes as they pass through a sterilization chamber will NOT be kind to your skin, your vision, or your long-term health. My uncle died of skin cancer, so I’m not kidding around with this stuff.

That said, step one of my plan is STUPID STUPID STUPID.

Aquarium UV clarifiers contain a UVC bulb, protected from water by a quartz sleeve, mounted inside of a black plastic chamber. The chamber has an inlet and outlet for water to flow through while microbes are killed.

Step 1: Cut a window in the side of the chamber and install a reflector on the opposite side of the chamber; this lets all the UVC light out of the side of the sterilization unit (as I said, STUPID, you shouldn’t do this at all)
Step 2: Mask off the live tissue of the tree using vinyl tape and heavy aluminum foil
Step 3: Mount the sterilizer lamp close to the deadwood to treat it with the UVC light
Step 4: Encase the light unit and the exposured area with cardboard and likely attach the aluminum foil to the box, the box will have a 12-volt fan mounted to it for heat, and light baffles to prevent UVC leakage

I have no idea how long this will take or how long to leave the light on each day. I’ll be watering the tree each day. Before I enter the greenhouse to do so, I’ll cut the power to the light. I’ll check on the setup each day to see how it progresses.

I’ll likely do this in my greenhouse with a “Caution UV Light” sign on the door.

Some other notes:

  • Valhala Wood Preservatives makes a product called “Lifetime Wood Treatment” which is supposed to be UV activated and ages the wood. It is supposed to be environmentally safe. The price is just at the level of being worth trying.

  • I have some bald cypress tree trunks that didn’t make it, so I’ll be experimenting on these first. They still have a nice golden look to them. I want to see if I can get the wood to silver.

  • The effect of UVC radiation on living plant tissue is unknown to me. Since only UVA and UVB make it down to the planet’s surface, it might be a bad idea to expose trees to UVC. That’s why I’ll be masking off the living parts of the tree.

  • UVA and UVB bulbs are available, but typically these are either used in tanning beds which makes them too long in length, or they are used in intense plant grow-lamps. While either light spectrum could be used to age wood, artificial light sources are not made to be intense enough to kill. I suspect that grow-lights will age wood slower than aquarium sterilizers. I’m not looking for a complete study on the three spectra and their efficacy in aging wood. If the UVC approach works, I’ll stop there.

  • Why am I cutting up an aquarium product rather than just building a cheaper alternative out of the base parts? The aquarium product is designed to keep the electrical components away from water. Anything I build is likely going to add the additional risk of electrifying me before I get the chance to develop melanoma.

EDIT: For clarification of some points


Hi @BillsBayou, interesting idea but I’m not sure how strong those UVC bulbs used in aquarium sterilisers are going to be compared to a season out in the sun of UVA and UVB. Worth an experiment, but I’d hypothesise the effects will be underwhelming on deadwood. Keep us updated. :smiley:

I agree about preferring to see the natural colour of deadwood and white deadwood not suiting most trees. A technique I use and have learned from Harry Harrington’s books/blog (although possible done elsewhere first) is to burn some newspaper and rub ash into the wood – best blotchy and not over-worked in – before applying your lime sulphur solution. It helps disguise the yellow/beige hues of the sapwood and heartwood (something I believe which would happen naturally with age) without necessarily making it overly light/white.


I like your idea for a control. From one piece of test deadwood, I’ll cut three pieces. One goes in the UVC aging box, one in the sun, and one in my garage.

The problem with a season in the sun for New Orleans is the humidity, the rain, and the termites. We suffer with Formosan termites. They eat the hardwood of live trees. Combine that with humidity and rain and things go bad in a single year.

As for comparing the amount of sun-damage from an aquarium sterilizer and a season in the sun, the sterilizer is supposed to kill organisms during the short time they’re in the sterilization chamber. I’m hoping that means it is intense enough to do some serious work on deadwood in a short amount of time.