How to Grow San Marzano Tomatoes

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.

Nutritional Value

One half cup of ripe San Marzano Plum tomato has approximately:

30 calories
6 g carbs
0 cholesterol
0 g fat
1.0 g fiber
1.0 g protein
220 mg sodium

Note: Obviously, the nutritional values above will vary depending upon the size of the fruit.

Roma Versus San Marzano Plum Tomatoes

San Marzano Tomato

Indeterminate habit

Few seeds and juice

Sweeter

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

San Marzano Tomato Plant Specifications

Days to Harvest: 70 to 90 days after transplanting seedlings into your garden, depending upon variety and growing conditions.

Plant height: 6 to 10 feet tall.

Light Needs: Full sunlight.

Ideal Soil pH : 6.0 – 7.0.

Plant Hardiness Zones: 5 – 10

Ideal Growing Temperatures:

Nighttime Lows: 60 – 70° F.
Daytime Highs: 70 – 85° F.

Plant Type: Annual.

Native To: Peru and other areas of South America.

Deer Resistant? No. Deer may nibble on the plant’s tender growing tips, especially if other food sources are scarce.

Botanical Name: Solanum lycopersicum

Toxicity: While the fruit is edible, the plant is mildly toxic to humans, dogs, cats, and many other animals.

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

Planting and Soil Needs

Select a planting site where your plum tomato plants will receive full sunlight. The plants grow their best in loose, rich, and well-draining soil. Mix plenty of compost into the soil. Next, mix in a general-purpose fertilizer that is high in nitrogen.

Just before planting the tomato plants in your garden, “harden off” the seedlings by bringing them outside during the daytime and for increasing hours, until you are leaving them out overnight. Use of a cold frame is recommended, but not a requirement. If frost is predicted, bring them indoors.

On planting day, pour liberal amounts of water with a soluble liquid fertilizer on the seedlings. Plant them in the garden carefully. To minimize transplant shock, avoid disturbing the roots. Normal spacing is 24” apart, in rows 30″ to 36″ apart.

Light Requirement

Grow San Marzano plum tomato plants in an area of your garden where they will receive at least eight to ten hours of bright, direct sunlight. For optimal growth and the maximum production of fruit, provide them with full sunlight from sunrise to sunset.

Fertilizer Needs

Like other types of tomato plants, San Marzano plum tomato plants are heavy feeders. So, fertilize the plants regularly. Early applications should be high in nitrogen. Importantly, as blossoming occurs, switch to fertilizers that are higher in Phosphorus and Potassium. Too much nitrogen fertilizer results in lots of lush green leaves, and little fruit. A fertilizer specifically formulated for tomatoes will help to maximize your crop.

You can also apply a liquid fertilizer. Spray the leaves of the plants. The leaves will absorb the nutrients. As a result, the leaves turn a deeper, healthier green color and more efficiently uses the sun’s rays.

Water Needs

Keep your San Marzano tomato plants well-watered. The goal is moist, but not wet soil all season long. As the season progresses, the roots go deep in search of moisture. Thus, in mid- summer deep watering is preferable over more frequent, light watering. Ideally, you want moisture to go deep to all the roots of the plant. Water directly to the roots. Keep water off the leaves if at all possible. Tomatoes are susceptible to plant disease that grows in wet, humid conditions.

Other Steps

Weeds compete with your tomato plants for nutrients and soil moisture. Thus, keep the planting area well-weeded during the entire growing season.

While plum tomato plants grow smaller than other varieties, it is still important to support the plants. If you use tomato cages, then these plants can still grow much taller than the top of the cage. We recommend growing them along a fence or loosely tied to a tall stake. Use jute strips of cloth, a soft rope to tie the plants to the fence or stake. More on staking tomatoes.

Mulch around the plant to retain soil moisture, and to keep the weeds down.

Also see:

Plant Problems

Soil Temperatures

Ideal Soil pH

Tip: Find a place along the back of the house for just one tomato plant. This one plant will be the last to succumb to frost in the fall. The warmth of the house, and a light plastic sheet or cloth tossed over it at night, will allow you to harvest fresh tomatoes after the first frost, right when prices are rising in the grocery store.

Cold and hot spells will affect fruit development and growth. Fruit set will not occur below 55 degrees or above 90 degrees Fahrenheit.

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

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.

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.

Plant Hardiness

When growing San Marzano tomatoes, it is important to note that they 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.