You can't measure C1 in-circuit because it's in parallel with a resistor and that screws up the meter's capacitance reading.
Whenever you measure resistance or continuity or capacitance, then at least one of the leads or terminals to which you are pressing the meter probes must have nothing else connected to it other than the specific item being tested (or multiple items being tested together as a unit). Freeing up the lead in question is difficult for items such as capacitors on a circuit board but is easy for things such as portions of a household branch circuit downstream you are checking for shorts.
Do you get coverage you can count on? From the bag of fertilizer? From your lawn sprinklers?