I have been growing San Marzano for years.
I use my saved seed each year.
Always grow them outside in pots.
I use 10 inch pots and fill them with about six inch of compost (so soil level about 3 inch from top) in the pot. I grow one plant within each pot. All pots sit side by side in a row.
I put in four poles that sit three feet above the soil level. Wrap string round all the poles every 4 inches or so.
Do pinch out.
Always get a great crop. Use them for my tomato paste and soup bases that I freeze and use throughout the year.
Will be sowing the first lot of seed in my greenhouse in small 2 inch pots later this week. One seed per pot, they germinate quickly about 7 days, ready to be planted into their final outside pots in early May and cropping from late May.
I water them a few times a week, in their outside position. Do have some that sit on soil and some that sit in trays.
Also feed them every fortnight with levington or similar tomato feed.
Living down here, they love our Sunny warm climate and last year with that long hot spell had double the normal crop.
They do stop producing in late September and for me have had no problems at all.
