growing bacteria on a petri dish
1 The ideal temperature for growing bacteria is between 70 and 98 degrees F (20-37 degrees C). 2  If necessary, you can place the petri dishes in a cooler location, but the bacteria will grow a lot more slowly.3  Leave the bacteria to develop for 4-6 days, as this will give the cultures enough time to grow. If necessary, you can place the petri dishes in a cooler location, but the bacteria will grow a lot more slowly. 2  Leave the bacteria to develop for 4-6 days, as this will give the cultures enough time to grow. 3  Once the bacteria begins to grow, you may notice a smell coming from the dishes.