How to Grow and Care for San Marzano Tomatoes
San Marzano is a variety of plum tomatoes, with thinner, elongated, and more pointed, meaty fruits than Roma tomatoes.
San Marzano's taste is stronger, sweeter, and less acidic, considered by many people to be bittersweet. San Marzanos are indeterminate, heirloom tomatoes.
Updated: December 3, 2022.
Intro To San Marzano Tomatoes
San Marzano tomatoes have thick meat and fewer seeds than many other tomato varieties and are used for canning (whole, chopped, strained), pasta, and pizza sauces, but also for salads, sandwiches, and many other meals and dishes.
San Marzano tomatoes are a very popular tomato variety grown all over the world. However, only San Marzano tomatoes grown in the Campania near Naples, Italy, have the right to be labeled as DOP (Denominazione d'Origine Protetta, Protected Designation of Origin) San Marzano tomatoes.
But that doesn't prevent home gardeners from growing this excellent tomato variety.
Are San Marzano Tomatoes Heirloom Tomatoes?
Yes, San Marzanos are heirloom tomatoes, and as such, they are an open-pollinated variety that breeds true from generation to generation, making seed saving possible for any home gardener - keeping the seeds from the best plants, local San Marzano plants tend to adapt to local conditions from generation to generation and evolve as high yield, resilient plants.
In order to keep genetic diversity, it is important to exchange seeds with other local gardeners and obtain seeds and plants from distant growers, from garden centers, or buy seeds online. Some "fresh blood" is required from time to time, not only when growing San Marzanos or just tomatoes, but all plants and animals in general.
Are San Marzano Tomatoes Determinate Or Indeterminate Tomatoes?
Unlike many other canning tomato varieties, San Marzano tomatoes are indeterminate tomatoes and very vigorous plants that produce a large number of fruits, thus requiring strong, sturdy, and tall cages or stakes.
Many plants bear fruits until frost, making these tomatoes especially suitable for growing in warmer climates. In colder climates, growing San Marzano tomatoes in pots and containers and moving them indoors when winter arrives can prolong the harvesting season even beyond the first frosts.
San Marzano Tomato Yield Per Plant?
San Marzano tomatoes are usually 2-3 inches long and weigh 3-4 ounces. They are ready for harvest 75-90 days after transplanting the plants to their permanent location after the danger of frost is gone.
On average, a single San Marzano tomato plant, with good support, regular watering, and nutrients rich soil, can bear 8-10 pounds (3.5-4.5 kg), sometimes up to 12 pounds (5.5 kg) of tomatoes.
Although originally grown as canning tomatoes, San Marzanos are indeterminate tomatoes that take a little bit longer to ripen fully - typical canned tomatoes are determinate tomatoes that are ready for harvest in 60-75 days. 
How to Sow and Transplant San Marzanos
Sowing seeds and growing young plants indoors, and transplanting them outside when the danger of frost is gone has many benefits when growing tomatoes, especially indeterminate varieties like this one.
Regardless if grown in a warmer or colder climate, San Marzanos should be sown early indoors and grown in a larger flower pot (for example, 25 cm (10 inches) in diameter) - this way, when the danger of frost is gone, you are transplanting the plants that are at least 50 cm (20 inches) tall, with the root ball still not filling entire flower pot.
In warmer areas, feel free to sow the seeds in smaller pots and transplant them to permanent locations when the plants are much smaller, for example, 10-12 inches (25-30 cm).
San Marzanos are sown in a good potting, well-aerated soil, rich in organic matter, that drains well - put the soil in the pot, press and compact the soil gently, and place a few (3-5) seeds on top of the soil, add a few millimeters of new soil, pack the soil gently again and water very gently.
To prepare the soil in the garden, add aged manure, compost/humus, worm castings, and some balanced NPK fertilizer like 10-10-10 or 15-15-15.
Tomatoes like nitrogen, and with nitrogen in abundance, they will grow fast and huge but prone to diseases and pests, with a limited number of flowers.
Many gardeners limit nitrogen when tomatoes start to flower, but indeterminate varieties require a balanced amount of nutrients since they grow for a long time - hence adding organic compost/humus, worm castings, or similar fertilizers, in the long run, feeds the plants with a constant flow of nutrients and improve the soil quality.
When planted on a permanent location, feed fast-growing tomatoes monthly with 15-20g (half an ounce) per plant of NPK 10-10-10 - this also depends on the plant size, number of fruits, soil type, soil condition, etc.
Also, adding periodically (every 2-3 months) a little bit of organic compost or worm casting feeds the plants without creating spikes of nutrients in the soil - and yes, half an ounce of balanced NPK fertilizer hardly can be regarded as a "spike of nutrients."
Soil Type For San Marzano Tomatoes
San Marzano tomatoes are originally grown around the Italian town of San Marzano, in vulcanic soil, giving these tomatoes a very nice taste and fragrance.
However, San Marzanos grown on various soil types also have great taste and aroma.
When choosing the soil, keep in mind that sandy soils have good drainage, but they don't keep nutrients well, while heavy soils have bad drainage.
The soil can be improved by adding aged manure and humus/compost, and other organic matter on a regular basis.
Decomposing organic matter also makes soil slightly acidic - the ideal pH for tomatoes is around 6.0 - 6.7, so feel free to test it every few years on several positions and depths in your garden.
In order to avoid root damage, many gardeners put stakes before they transplant tomatoes or position and fix tomato cages right after transplanting plants.
Growing San Marzano Tomatoes in Flower Pots and Containers
Growing tomatoes in flower pots and containers have many benefits, especially when growing indeterminate varieties in a colder climate.
Being large, fast-growing plants, San Marzano tomatoes require large pots and containers - around 35-40 l (10-12 gallons) of growing soil is required/recommended per plant. Of course, they can be grown in smaller pots and containers, but they must be watered and fertilized more often.
Growing plants in pots enable the gardener to optimize soil according to the exact needs of the plant - use good sterilized flower soil, and add some fertilizers for tomatoes and organic matter.
Since root ball and the soil is limited, using NPK fertilizers with gradual release of nutrients is highly recommended, especially when tomatoes are grown indoors and various smells from the soil must be avoided (aged manure is relatively neutral regarding smell when compared with ordinary manure, but in a closed area people will notice it quickly!).
For example, a 16-inch (~40.6 cm) tall and 16-inch wide pot is large enough for a single San Marzano tomato plant, while 20-inch (50.8 cm) tall and 20-inch (50.8 cm) wide pot is generally large enough for 2 San Marzano plants.
Although larger pots can be found and used for planting 3 or more San Marzano plants, such pots, when filled with potting soil, can be rather heavy and thus very difficult to move around if required.
If needed, place pots with San Marzano tomatoes on the trollies with wheels, and move them indoors if there is a danger of frost during the night or when winter arrives, which can significantly prolong the harvesting season.
Before filling the pots with good potting soil, make enough drainage holes in the bottom - San Marzano tomatoes like well-aerated, slightly acidic (6.0-6.7 pH), and moist soil, but soggy soil can cause various problems.
While filling the soil, be sure to add organic compost and/or worm castings, and NPK fertilizers with the gradual release - the soil must be nutrient-rich, but it is more important that the amount of nutrients doesn't fluctuate much, which can be challenging when growing the plants in smaller pots.
Right after planting, place a tomato cage or some other form of support for the tomatoes - the roots of the plants grown in the pots tend to be very sensitive to mechanical damage.
Placing mulch around the plants can protect the soil from wind and sun, can prevent weeds from growing, and, as the mulch decomposes, it refeeds the plants slowly and keeps the soil slightly acidic.
After planting the San Marzano plants, be sure to water the pots regularly - during the summer heat, pots must be watered practically on a daily basis, or one should add a drip watering system.
Note: Drip watering systems vary from ordinary plastic bottles with slow-release valves to automatic irrigation systems controlled by WiFi and Bluetooth-enabled controllers.
Regular watering is very important since fluctuations in moister levels can cause issues with plant growth, flowering, bearing fruits, etc. - practically everything about growing healthy and strong tomato plants.
Caring for San Marzanos in pots is practically the very same as caring for San Marzanos planted in the soil patch - except for the watering and the fact that San Marzano tomatoes planted in pots can be carried indoors before first frosts. And if they continue to flower indoors, be sure to pollinate them manually.
Caring for San Marzanos
Everything said about other varieties of tomatoes applies to San Marzano tomatoes as well.
Prune side shoots when they start to grow. Also, remove anything that is ill, broken, damaged, or similar.
Water plants regularly, and during summer extreme heat, water them every day or every other day depending on the quality and depth of the soil.
Plants in pots should be watered daily during summer.
The use of a drip watering system keeps the moisture levels very constant and saves water, which can be very important over a longer period of time.
San Marzanos are rather resistant to verticillium and fusarium wilt and, being strong plants, can tolerate few bugs/pests.
In the case of a stronger attack, chemicals must be used, but be very careful during the bearing season. It is better to throw away a few ill branches/fruits and keep garden chemicals free than to use the chemicals.
Note: never plant tomatoes on the patch that previously had tomatoes planted. Also, planting a few tomato companion plants near the tomato plants can help repel pests and improve the health of tomatoes.
End of Growing Season
Like other tomatoes, San Marzanos are sensitive to frost. When there is a danger of frost, pick green tomatoes and try to ripen them indoors. Remove plants from the soil patch and use them for making compost; remove and clean stakes and cages for next season.
Add some aged manure and balanced NPK fertilizer and dig them into the soil some 20-25 cm (8-10 inches) deep and let the patch rest till late winter or early spring - when the time comes, plant other plants having crop rotation on your mind.
Tomato family: tomatoes, peppers, eggplant, potatoes - never grow them one after another. Consider sweet corn before and beans after tomatoes - such rotation can drastically lower issues with pests and diseases and help avoid using chemicals.
San Marzano tomatoes grown in pots and containers can be moved indoors and grown during the winter - just be sure to provide them with some warmth, sunlight, water, and nutrients, and don't forget to manually pollinate them if You wish your tomato plants to bear new fruits.
San Marzano Tomatoes Cuisine
San Marzano tomatoes are originally grown for canning, but they are also used for making sauces, purees, salads, and similar.
With Fish and Meat
Just a few San Marzano tomatoes added to the main meal as a salad can change the aroma and flavor of the whole meal.
Also, healthy and fully ripe San Marzano tomatoes can be rather decorative.
In Salads
San Marzano tomatoes in salads can be mixed with cucumbers, peppers, green onions, and similar veggies. Add some olive oil, vinegar, and a little bit of salt, and the great-tasting and very healthy salad is prepared in no time.
Also, feel free to mix San Marzano tomatoes with other tomatoes as well.
Long Story Short: San Marzano tomatoes are one of the varieties that should be grown in every home garden - 3-4 plants can constantly supply fresh tomatoes for a long period.
Combine them with a few yellow/red/black cherry tomatoes and perhaps with a few other interesting varieties, and you will have some 20 tomato plants bearing various fruits during the entire season - tomatoes suitable for salads, sandwiches, sauces, canning, etc.
Good luck! :)
P.S. When buying canned Sam Marzano tomatoes, be sure that they are "DOP San Marzano Tomatoes."