I went in summer (end of July) so the flowers were blooming. The English audio guide was useful.
Note: remember to exchange your booking with a voucher on the day of the trip from the 2nd floor sightseeing counter (It says "CHUO BUS" at the front and "Chuo bus regular sightseeing bus counter" at the side). Easiest way to find it is when you approach the Sapporo station building from the OUTSIDE and from the bus station side, there's a big-ish staircase that you can see near the taxi stand. Just go up there and through the glass door.