Honey works. The bio-herd needs carbs to grow and even tho the roots give up sugar for them adding some boosts their growth rate so they can convert more organic stuff into food the plants can eat. Keeping the root zone warm helps with that too.
Molasses might work a little better but good unpasteurized honey has lots of micro-nutrients as trace elements in it too.
The bag of carbs I got from Greenleaf is just pure dextrose so nothing but sugar so I give the plants some molasses too. Organic un-sulphured blackstrap stuff.