First of all, Bobert, absolutely do not 'impound' the stuff and set yourself up as an authority cum jail garden. That would be very bad for the relationship between you two. You are both adults and need to respect one another as equals.

Next, ask yourself why the P-vine is forgetting stuff. Does she have too many things to do? Does she have to move on to job no. 2 before she can finish job no. 1?

With small tools, is it a visibility issue? Can you spray paint the handles so they don't disappear when set down, etc? Can you supply a handy system for keeping track of everything and getting it organized? Some kind of cart?

Saints forfend, is she getting forgetful because her health is weakening? Do you need to talk to the doctor about this? Think it over.
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Sorcha, Bobert lives in West Virginia. The problem isn't watering stuff. The problem is hacking back the jungle that thrives in the warm, wet climate.