Hi Julia,

Lysimachia nummularia can actually be grown as a bog plant near ponds, and if it's close enough to the water the stems will float out onto the water and grow roots into the water, so keeping it in a tray of water is an excellent idea to keep it healthy while you're gone.

Have a great vacation,
Skybird

I have creeping jenny mixed in with Mazus on the waterfall part of a koi pond. As soon as it grows big enough for the water to splash it it goes crazy. Its been there for 3 yrs and just loves the water