The higher the temperature, the more easily sugar dissolves in water, and so existing sugar crystals will dissolve. At lower temperature, they will precipitate.

I found a site where you can read about the different factors that affect the crystal growth. I recommend you to visit this site on the link below and read it. There are also amazing pictures that you will enjoy very much.

crystal growth

Here it says that evaporation affects the common crystals most strongly. Temperature also affects the growth of crystals because "the higher the temperature, the warmer the crystal solution will be, and the faster its molecules will move. This movement allows them to evaporate more quickly, leaving particles behind to form into crystals. This means that a warm solution or a warm room will allow crystals to form more quickly than a cold room."