Give the substitute enough context for an unusual day
Walk through one instance of the job while you are available. For the plants, show the two pots that dry quickly and the one that usually stays damp. Explain what the temporary owner should do if a plant looks different from usual or the watering can is missing. Ask them to show you the next action once. A quick demonstration often reveals missing information that neither person thought to put in the instructions.
State exactly when responsibility returns
Set the return date for responsibility. If the traveler comes back late, decide whether the temporary owner covers one more watering. This avoids a gap on the return day when each person thinks the other has resumed the job.
Confirm what happened before resuming the job
When you get home, ask for the last action and any unresolved issue rather than repeating the whole temporary routine. “Both window pots watered Tuesday; large pot still damp” gives you a usable starting point. If your return shifts by a day, ask whether the helper can cover the extra day and wait for an answer. Being available for a defined week does not commit them to covering an open-ended extension.