Carpenters, botanists, etc: Do I need a special varnish for a plant box?

[mercanucaribe]

I want to put some plants in a wine box, but don't want the wood to decay from the moisture or chemicals in the soil. What varnish should I use to ensure that the wood stays sealed, but that won't break down and poison the plants?

 

[zerocool1]

I'd just fit a pot in the box....

 

[mercanucaribe]

I don't want pots in the box. I want dirt in the box, and lots of plants and moss growing!

 

[myusername]

Thompson's water seal.

 

[damonpip]

Exterior Polyurethane

 

[shilala]

You'll have to sleeve and seal the weep holes, caulk all the seams, and go through sheer hell to keep them from rotting out.
Use liners or build a box to fit around a pot.
What you're trying to do isn't done because it doesn't work.
I use hayrack planters lined with cocoa fiber. They kick ass.

 

[mercanucaribe]

I'm not worried about sealing all the seams and holes, because the soil has to drain anyway. I'll be drilling drain holes in the bottom.

Would shellac be okay?

 

[shilala]

Originally posted by: mercanucaribe
I'm not worried about sealing all the seams and holes, because the soil has to drain anyway. I'll be drilling drain holes in the bottom.

Would shellac be okay?

Shellac takes up water. A high grade marine varnish would be your only hope. Line the box with plastic, too.
You have to seal the seams because everywhere the water goes through will stay wet at all times because of the soil's moisture content.
The drill holes will need to be varnished/sealed, too.

 

[mercanucaribe]

What a pain in the ass! Okay I'll figure out how to line the box with plastic and epoxy and use marine varnish.

 

[shilala]

Originally posted by: mercanucaribe
What a pain in the ass! Okay I'll figure out how to line the box with plastic and epoxy and use marine varnish.

...and when you're done with all that the box will still rot out. That's why it's not done.

 

[mercanucaribe]

I got this stuff.. Thompson's WaterSeal, for wood, concrete, terra cotta, in a spray can. It says it prevents water damage and "allows wood to grey naturally". The Thompson's brand stuff made especially for wood doesn't say anything about greying. Should I be worried about that?

 

[mercanucaribe]

Or does wood grey because of UV?