San Marzano Tomatoes - How to Grow and Care for San Marzanos
San Marzano is a variety of plum tomato, 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: June 6, 2022.
San Marzano tomatoes have thick meat and fewer seeds than many other tomato varieties and are used for canning (whole, chopped, strained), for pasta and pizza sauces, but also for salads, sandwiches, and for many other meals and dishes.
Being heirloom tomatoes, San Marzanos 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.
San Marzanos are also 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.
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 Marzano 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.
San Marzanos are sown in a good potting, well-aerated soil, rich in organic matter, that drains well - put the soil in the pot, pack the soil gently, 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, and soil condition, etc.
Soil type - 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 more on this topic, check the Growing Tomatoes Indoors and Outdoors in Pots and Containers article.
Caring for San Marzanos
Everything said about other varieties applies to San Marzanos.
Prune side shoots when they start to grow. Also remove anything that is ill, broken, damaged, and similar.
Water plants regularly, during summer heat every other day and during extreme heat, every day. Plants in pots should be watered on a daily basis. If possible, use a dripping system regardless if growing tomatoes in the pots or not - constant moisture helps plants grow healthy fruits without deformations of any kind.
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.
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 the use of chemicals.
San Marzano tomatoes grown in the 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 tomatoes to bear new fruits.
Long Story Short: San Marzano tomatoes are one of the varieties that should be grown in every home garden - 3-4 plants can supply constantly fresh tomatoes for 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! :)