For this quest objective you need to have a specific number of your plants at a "happy" temperature. A happy temperature is the ideal temperature for a plant to achieve a temperature bonus bud. You can see what each strain’s ideal temperature is from the icon on the strain information pop-up. (And they will have a green smiling icon appear above their pot in the greenhouse when you adjust the temperature to their favored range)

In the 1st greenhouse the AC unit controls the temperature for all the pots in that room, in the 2nd greenhouse each row of 3 has its own AC control unit. Some strains like it hot and some strains prefer it cool, so be sure to check out a strain’s information before you plant your buds!