My tomatoes are splitting HELP

The problem of cracking is exacerbated by hot weather and uneven
moisture, but Jacob Mittleider gave me pictures of research he
conducted in recent years which taught him that boron deficiency also
played a part. In addition to making sure you are doing what is
possible to give the plants some relief from the hot sun (mid-day 50%
shade), and watering every day, i would give them a shot of boron -
about 1/2 teaspoon per foot of row.