Illegible labels are a heartbreak, that's for sure. On top of the
excellent observations that have already been made, I'll add a few of my
own.

Pencil is good, but only if you swap out the labels every few
years or so. Plus, it smears.

The "Sakura" Ident-I-Pen is like Sharpie, except the Sakura is
archival-quality. Side-by-side, Ident-I-Pen lasts much longer than
Sharpie. Both should be available at good art supply stores, or on the
web. Sakura costs a little more, but I have one pen that's going on 4
years old that still writes. They write on glass, metal, plastic, etc.

For label printing, there are two types of thermal printing
(ignoring ink jet, laser, etc. for now)- direct, and thermal transfer.
Direct will fade over time. Thermal transfer uses a special kind of
printer in conjunction with wax or polymer ribbons. Thermal transfer
printers come up constantly on eBay- I prefer Datamax. I own four of 'em.
I don't think they make plant tags specifically, but EIM Inc. makes all
kinds of label solutions for wet and hot environments, as well as to
resist chemical exposure. They're at www.eiminc.com.

Last suggestion: The most valuable plants- particularly those that
will leave the greenhouse where sweaty little hands will undoubtedly
remove your tags, probably to the wrong plant- should have another label
made each time you repot them. It should be placed all the way at the
bottom of the pot during repotting, where the sun don't shine. :-)

The address in the header doesn't work. Send no email there.

-AJHicks
Chandler, AZ