San Marzano Indeterminate Tomato

Start seeds indoors 6 to 8 weeks before your last frost date. Sow seeds about 1/4 inch deep in moist seed-starting mix and maintain soil temperature between 70 and 80 degrees Fahrenheit for reliable germination. Provide bright light as soon as seedlings emerge, either under grow lights or in a sunny window, to prevent legging.

Transplant hardened-off seedlings outdoors after your last frost date when soil temperature reaches at least 60 degrees Fahrenheit, ideally closer to 70 degrees. Space plants 18 inches apart with 36 inches between rows. Bury the stem deeper than it was growing in its container; tomatoes will develop roots along the buried stem, creating a stronger root system.

Harvest San Marzano tomatoes when they reach full color (deep red) and yield slightly to gentle hand pressure. For paste and sauce applications, you can harvest at the breaker stage when the first blush of red appears on the shoulder of the fruit, as the tomato will continue ripening off the vine and you'll encourage more flowering. Twist gently or use pruning shears to detach fruit from the vine, being careful not to damage the fragile stems. Continue harvesting throughout the season as the indeterminate vines produce new flowers and fruit until frost arrives.

Prune suckers regularly on indeterminate San Marzano plants to direct energy toward fruit production and improve air circulation. Suckers are the small shoots that grow in the crotch between the main stem and side branches; removing them focuses the plant's resources on fewer, higher-quality fruits. As vines grow tall, remove lower leaves once the plant is well-established to further improve air flow and reduce disease pressure. Maintain a single or two-stem system for maximum productivity and easier harvesting.