If you grow them outdoors then sow the seeds from March – May in a good quality seed compost and cover lightly (appx 2 – 3 mm) with vermiculite or compost. Not all canned tomatoes from Italy are San Marzano, and, to make things more confusing, San Marzano tomatoes grow outside of Italy, too. Tomatoes like Roma or San Marzano are very easy & satisfying to grow indoors at home. I have put two in a pot ( 20 liter capacity). San Marzano is an indeterminate type paste tomato, so the techniques are pretty much the same as for any long-season tomato. Tomato plants are transplanted as shown in the picture below. Italy's secret to full-flavored tomato sauces has reached beyond its borders; you can buy seeds or seedlings and grow this marvel in your own garden, wherever you are. And a growing light, example below. Find help & information on Solanum lycopersicum 'San Marzano' tomato 'San Marzano' from the RHS The San Marzano tomato is a type of plum tomato, and it's longer and thinner than the typical plum tomato you might see sold fresh in grocery stores or buy canned. Depending on where you live in the world start sowing your tomato seeds late winter if you are planting in a greenhouse or early spring if you are growing them outdoors. And in my experience it does grow too big! Tomato plants needs lots of nutrients in the growing phase and during fruiting phase. It's a complete thug and will take over the greenhouse if you let it - but it does give lots of good tomatoes which I find are excellent for roasting! This is my third year growing San Marzano and the seed packet says it's a semi-determinate - may require support and sideshoots removing if it grows too big. 2 Items you will need. San Marzano. I grow my tomatoes in compost’able cardboard pots. San Marzano tomatoes have become the darling of the gourmet world. … Growing San Marzanos from seed takes a bit more effort but is worth doing as you can get more plants for your money. If you want to start growing tomatoes indoors you will need. Either soil & a plant pot or a hydroponic system – 2 example units are shown below. Growing San marzano tomatoes. They also have fewer seeds than typical plum tomatoes. Grow San Marzano Tomatoes From Seed. The ideal potting mix for growing tomatoes in pots are a mixture of cocopeat and compost, if one wants to grow them organically. 2 Ways to grow the San Marzano Tomato at home You can either grow a San Marzano Tomato indoors or outdoors. How to start growing tomatoes indoors.