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San Marzano vs Roma

Both are red plum tomatoes bred for cooking, and both turn up in every seed rack, but they are not the same tool. San Marzano is the celebrated Italian sauce plum; Roma is the compact, dependable garden workhorse. The difference shows up in the pot.

San MarzanoPaste
San Marzanoopen-pollinated · 85 days · LateCompared with Roma, San Marzano is described as stronger, sweeter and less acidic, with thicker flesh and fewer seeds, which is why it is the benchmark sauce and canning tomato. Attributed description, not a measured claim.
RomaPaste
Romaopen-pollinated · 75 days · MidDescribed in catalogs as mild and sometimes tangy and meaty, valued more for firm, low-moisture flesh than for bold taste. This is the recurring catalog and grower description, not a measured claim.

Both are paste tomatoes

Each carries dense, low-moisture, meaty flesh with few seeds, which is what makes a paste tomato cook down into thick sauce without watering it out.

Flavor and flesh

San Marzano is described as stronger, sweeter, and less acidic than Roma, with thicker walls and fewer seeds, which is why it is the benchmark for sauce and canning.

Roma is milder and a touch tangy, valued more for firm, reliable, low-moisture flesh than for bold taste.

In the garden

This is the big practical split. San Marzano is a tall indeterminate vine that needs staking and bears over a long season. Roma is a compact determinate bush that ripens a concentrated crop, handy for a single batch of sauce, and carries VF disease resistance. Both can be prone to blossom-end rot in dry or uneven watering.

Common questions

Which makes better sauce?
San Marzano is the classic for rich, sweet sauce. Roma is easier to grow and gives a concentrated determinate crop, good when you want to can a batch at once.
Can I save seed from either?
Yes. Both are open-pollinated and come true from saved seed, unlike hybrids.

Sources