We addressed this and other common tomato problems in a recent issue of the All-Seasons Garden Guide. Here’s the suggestion:
--Blossom End Rot is often caused by fluctuating soil moisture, such as a dry period followed by lots of rain, and is evidence of calcium deficiency in the fruit. Too much nitrogen, high salt levels in the soil, or root damage can also contribute.
--Symptoms: A dark or water-soaked area on the first few fruits’ blossom end (opposite the stem) that eventually enlarges, turns brown or black, and becomes sunken and flat; leathery skin on fruit. Note: Fruit does not rot unless secondary organisms invade. Tomatoes grow slowly and may ripen prematurely.
--To avoid: Prepare deep, well-drained soil. In low-calcium soil, apply lime. Avoid severe hardening off. Plant in warm soil. Water uniformly and regularly; provide mulch. Cultivate shallowly. Avoid overfertilizing; use nitrogen forms that do not contain ammonia, which inhibits calcium uptake.
--To control: Remove affected fruit.
--As for staking later in the growth cycle—sure. Just try to avoid piercing the plant’s roots. Put the stakes (or whatever) at the edge of the pot. Or, if available, tie the branches of the plant to something nearby, such as the railing of a deck.
--Regarding the whitish color, It’s hard to tell at this distance, but it may not be a problem. Perhaps there is the long-shot possibility that the you have a white tomato variety....that the plant tag was inadvertently changed before you bought it.
Good luck! And remember that every growing season is an experiment...