A good label for outdoor use can be made from soft, pure aluminium
strip, sold by roofing merchants as flashing for aluminium roofing.
I obtain it in strips about 2" wide, pre-primed with a grey paint which
makes it reasonably unobtrusive in the garden. I cut it to the
required size with scissors (it's very soft), place it on a yielding
surface, such as cardboard, and write on it, firmly, with a ballpoint
pen. This embosses the lettering into the aluminium.
Being soft and flexible, it can be wrapped around a plant stem and
will open out as the plant grows, or can be stuck, carefully, into
the ground, or can be wired on with aluminium wire. It will also
accept adhesive labels from the Brother P-Touch labelmaker, another
excellent aid for gardeners. Ideal for repetitive printing of long
plant names, and the labels seem very durable, and will stick to pots
or labels or even plant surfaces.
I presume north americans do use aluminium roofing, so can obtain the
flashing. If not, thin copper sheet should also work, but might cost
Rotorua, New Zealand