This beer was a tribute to my friend L., who supplied both the lemon verbena (from a huge plant she has in a pot) and the wild ginger (from a bed in her garden that needed thinning).
She’s also the inspiration for my occasional use of gentian in homebrewing, due to her enthusiasm for the soft drink Moxie, which includes gentian. I don’t know whether gentian has any anti-microbial properties, but this beer did not go off. That might actually be due to the lemon verbena, a medicinal plant which “contains a substance that might kill mites and bacteria.”
I found out subsequently that Asarum species such as wild ginger might be toxic in higher doses, so I’d really recommend using the similar tasting but unrelated ginger root that you buy in a supermarket, Zingiber officinale.
I added the wild ginger 20 minutes before the end of the boil and the lemon verbena right at the end, letting it steep in the hot wort for ten minutes before cooling. The gentian root goes in at the beginning of the boil, and yes, one teaspoon is plenty bitter!