How to Grow San Marzano Tomatoes

Roma Plum Tomato Plants

About San Marzano Tomatoes Variety

While Roma tomatoes, may be the King of plum-type tomatoes, the San Marzano variety deserves a spot in your home vegetable garden. Some gardeners and even some chefs, will tell you it’s the better of the two. We think you should be the judge. Therefore, we challenge you to do three things. First, read this guide on “How to Grow San Marzano Tomatoes”. Second, armed with this knowledge, buy a packet of both these varieties and grow them side by side in your garden. Finally, take the taste test. Use both of these varieties fresh and in recipes. Then, you can determine which is better.

The sweet-tasting San Marzano tomato is less acidic than other varieties. Low acid content just may tip the scales in favor of growing this great tomato variety.

Give San Marzano a try this gardening season. You will be glad you did!


San Marzano Tomato Description

Indeterminate vines produce plum tomatoes that are slightly more pointed than Roma.

San Marzano tomatoes have a thick flesh, and few seeds. The fruit is bitter sweet, and is less acidic than other plum type tomatoes.

Growing Tip: Indoor starts need at least 12 hours of full sun light. Provide grow lights as needed.

San Marzano Plum Tomato History and Origin

According to folklore, San Marzano seeds were brought to the New World in 1770 as a gift from the Viceroy of Peru to the King of Naples.

It was commercially introduced to the United States in 1926. 

Roma Versus San Marzano Plum Tomatoes

San Marzano Tomato

Indeterminate habit

Few seeds and juice


Stronger taste

Thicker flesh

Thinner, less pointed

Far superior for commercial canning in metal cans

Less carbs

Zero Fats

Roma Tomato

Determinate habit

Considered easier to grow

Few seeds and juice

More fiber

More acidic

Low in fat

Less susceptible to blossom end rot

How to Start San Marzano Tomato Seeds

Tomato plants are usually started indoors. Planting plum tomato seeds is an exciting time. It is one of the very first gardening projects of the year. After a long winter, you are itching to get your hands back into some “dirt”.

Begin starting San Marzano tomato seeds indoors in small containers, eight to ten weeks before the last frost date for your area. Sow tomato seeds about 1/8″ inch deep, using seed starting soil. Seeds will sprout in 10-14 days, depending upon soil temperature. Sprouting tomato seeds is quicker and more productive when using a heated germination mat.

As soon as the seedlings emerge, they need full sunlight to grow sturdy. Lack of sunlight causes the plants to grow “leggy”. Use grow lights to supplement the amount of available sunlight.

Tip: To help your plants grow sturdy, place a small fan on low nearby. Or, lightly brush the tops of the plants with your hands a couple of times each day.


How to Grow San Marzano Plum Tomato Plants

Learn all about growing San Marzon plum tomatoes:

  • How to Grow Tomatoes – From planting seeds to harvesting fruit, we’ve gotcha covered.
  • Staking Tomato Plants – Large plants and huge tomatoes require a sturdy tomato cage or staking to help avoid plant disease and keep fruit off the ground. 
  • Pruning Tomatoes – In fact, pruning helps avoid plant disease.
  • Plant Problems and Disease – Above all, remember the old saying “an ounce of prevention is worth a pound of cure.”

Tomato Cages and Staking Plants

San Marzon tomatoes are an indeterminate variety and require either staking or caging for optimum plant health and maximum fruit production.

Maximize your crop, and minimize disease and insect damage, by staking or caging tomato plants. As a matter of fact, all plum tomato plants benefit from caging or staking the plants. They will reward you with more tomatoes. The fruit will be cleaner, as they will not be sitting on the soil. More on staking tomatoes.

Insects and Pests

Tomato plants can experience insect problems with tomato hornworms, cutworms, and a few other garden pests. Also, if not staked or caged, snails and slugs will munch on the ripening fruit.

Birds will occasionally peck holes in red fruit.

Did you Know? Tomato plants emit a mild toxin that discourages many small insects from bothering them. This toxin can also cause skin itching and irritation.

About Tomato Hornworms

More on Tomato Plant Problems

Tip: Borage plants can be used as companion plants, to deter Tomato hornworms

Did you Know? Tomato plants (not the fruit) are used to make an organic insect repellent. See Tomato “Juice” Spray

Plant Disease

Several plant problems can arise, usually in the mid-summer heat and humidity. Blights and fungus infections can occur in high humidity. Early treatment with fungicides is effective. Spacing plants too close cuts down air circulation and promotes disease.

Blossom end rot can also affect the fruit. This is a round, brown, indented spot on the bottom of the tomato. It is caused by either uneven watering or a lack of calcium in the soil. Importantly, San Marzano tomatoes are more susceptible to blossom end rot than other varieties. More on Blossom End Rot.

Garden Tip: Do not water at night if possible in hot and humid weather if possible. Moisture and humidity combined with high temperatures promote plant diseases. If possible, water at the roots. 

More on Tomato plant disease

Plant Hardiness

Tomatoes like it hot! They will die if exposed to frost. Make sure to plant them after the last frost.

Tip#1: Cover your young seedling if frost is predicted. A simple and easy cover for small seedlings is to buy large or extra large plastic disposable cups. Place them over the seedling at dusk, and remove them in the morning. It is usually little or no wind on nights with frost, so they are not easily tipped over.

Tip#2: If you get a light frost overnight and you did not cover up your plants. Go out early before the sun rises, and spray your plants with the garden hose. This melts the ice off the plants and may save them.

Harvesting and Storing Tomatoes

Days to Maturity: 80 days from setting plants out in the garden.

Harvest plum tomatoes when they are fully red. You can pick them a few days before peak ripeness.  Then, they will store a little longer.

Importantly, do not pull the fruit off the vine. This can cause tears. Gently, twist the tomato off of the vine.

Garden Tip: Do not keep tomatoes in the refrigerator. They last longer and stay fresh longer if left in a bowl.

Garden Tomato Recipes

May we suggest:

When making large amounts of juice or sauce, you will need a tomato strainer and sauce maker, to easily remove seeds and skin.  See Tomato Strainers.

Related Articles

On the Light Side: See Tomato Trivia

Tomato Mania – In-depth information and advice from Garden Hobbies

Problems with Tomatoes – To begin with, an ounce of prevention is worth a pound of cure

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