My husband bought this roma tomato plant from our local nursery. I'm not sure how well it's been cared for though. Many of the tomatoes are black on the bottom. I googled this and saw it could be blossom end rot. How do we address this and get this plant/tomatoes healthy?

Yes, it's blossom end "rot". Actually a deficiency of Calcium, usually from too frequent watering. Give it some all-purpose fertilizer, maybe some Calcium (from garden lime) and don't keep it too wet. The bad ones won't get better, but new ones should be.

Adding calcium likely will not make a difference - getting it out of that pot and into soil where there is ample access to nutrients will. There is generally enough calcium in garden soil, it is sometimes unavailable to the plant due to cultural issues.

Prepare your planting spot, strip the yellowing leaves and fruit, plant it deep, keep it moist but not wet.

Roma is a direct descendant of San Marzano, meaning you are likely to lose part of the production to BER no matter what you do. The curse of San Marzano is an extremely high genetic predisposition to BER the further growing conditions are removed from those of the Sarno Valley, where San Marzano tomatoes originated. There is literally nothing you can do about it.

If you can keep losses below 10% (potted plants suffer from it in worse measure than those planted in the ground) you are doing great. If your losses are higher consider switched a different cultivar next year.

In addition to the BER, your plant looks as if it has a disease. If it were me, I would chuck the plant and get a healthy one.

gardenfish said:In addition to the BER, your plant looks as if it has a disease. If it were me, I would chuck the plant and get a healthy one.

It's not diseased, merely overwatered: mine looked exactly like that when I was moving and tried growing tomatos in containers.
"Oh, the poor dears must be thirsty in this heat" so I watered them once or twice a day and they looked much worse than this one. And I went nuts thinking they had some rare disease.
Learn from my mistakes before going nuts yourselves.

The yellowing looks like it could be a nutritional deficiency. The pot is rather small for the size of plant and I agree it would be better planted or, if it can't be, then transplanted to a bigger pot. I had problems with blossom end rot when I tried growing tomatoes in containers, my understanding was that it related to fluctuating moisture levels and that fitted the history at the time.

Sue, you may be right about the nutritional deficiency. Mine had this early on in the season when we had so much rain. The fertilizer was getting washed out of the pots faster than I could replace it or the plants could take it up.
As far as watering pots, all it takes is to insert a finger around 2" inches into the soil to see if it needs watering or not. Of course, gardeners have no control over the rainfall. The best we can do is make sure the pots we use have excellent drainage. And lack of certain nutrients can lead to weakened plants, making them susceptible to BER and diseases. For the record, I've never had BER, and I've been growing tomatoes in pots for 21 years.

In potted plants nutrient deficiencies are always (always) the result of excessive watering. Sadly sometimes this cannot be avoided as some plants (Hydrangea, Celosia etc) need to be watered very often when container-grown.

A well drained container will not just avoid root rot, but will unfortunately also leach out nutrients at a very high pace: it just cannot be avoided. That's why overwatered plants (or plants requiring lots and lots of water like potted Hydrangeas in hot weather) always look like they have an impossible collection of symptoms that look like nutrient deficiencies.

To avoid this we need to supply a ton of extra nutrients in readily available form, meaning liquid fertilizers applied through drenching or foliar sprays. Again here not all fertilizer were created equal, but you already know that.

Well, duh! And You know I say this fondly, ElPollo. I have the highest respect for your expert knowledge.
You sure opened my eyes about TMV.