You would make sure all plants in both groups were the same distance from the window, got the same amount of water, were at the same temperature, had the same soil and pot size, etc.
(You; would make; sure all plants in both groups were the same distance from the window, got the same amount of water, were at the same temperature, had the same soil and pot size, etc.) (all plants in both groups; were; the same distance from the window) (all plants in both groups; got; the same amount of water)
You all plants in both groups all plants in both groups
would make were got
sure all plants in both groups were the same distance from the window, got the same amount of water, were at the same temperature, had the same soil and pot size, etc.
the same distance from the window
the same amount of water