Wish I had read this earlier. This morning I hauled, too many to count, pitchers of rain water to potted plants having to mix a tablespoon of MG in each gallon. for this wonderful time saving idea.

This is a good idea!
I will use it for potted plants.
For plants in the ground, I use a siphon that attaches to the water tap.
It came from Lee Valley tools.
The siphon is placed into a concentrated solution in a pail near the tap.
As the water passes the siphon , it sucks up the fertilizer.