I've been giving some thought to this transplant vs seed question this year in conjunction with my direct seeding experiment and working in a
greenhouse that sells organic tomato starts.
Just with the variety Sweet Cherriette alone I have quite a few observations. I saw it in the Adaptive Seeds Catalogue and it was a must have for a direct seeding experiment. A 35 days to maturity from transplant current tomato bred by Tim Peters. I was like "wow!" And ordered the large size seed packet.
So I took the seed and put in a 4 foot long strip in the March seeded experiment. I also started starts inside one of which I planted outside on the last day of April and the rest in Early May. The may 15th frost I encountered equalized the heights on these for the most part.
Of the March planted direct seeded seedlings one is about to flower it's first blossom- it may be the first direct seeded seedling to do so.
However the transplanted and frosted seedlings all resprouted. Some of these are doing great and are now flowering profusely.
Then I had the packet in my pocket at work and since the seed was organically grown I offered a bit to my boss. So I ended up seeding a community flat with ~50 seeds. When it came time to transplant them my boss only wanted 6 so I ended up taking 41 seedlings home.
We were fertilizing at work with a couple of high P fertilizers and at home I was using Alaska 5-1-1 and natures choice organic miracle grow 10-3-6. We ran into some environmental problems at work with the weather and some of our tomatoes got some yellowing. Also in my
greenhouse at home it got really hot. The fan on the greenhouse kept tripping the reset on a ground fault interrupted outlet and the tomatoes left in there just loved the heat!
Anyway the 6 plants I left at work stayed tiny. Those I took home and transplanted into slightly larger pots grew better. However I transplanted two into gallon pots and one of these two hit the jackpot of perfect tomato growing conditions. It got to about a foot high and a foot wide while it's former flat mates stayed much smaller. I reckon if I had the skill and time the entire flat could have done the same. I also transplanted it outside into it's final home a five gallon pot and it didn't seem to suffer.
So with this one variety I've seen a range of errors and potentials with transplanting vs. Direct seeding. I've also learned especially with small seeded varieties and species that it takes a lot more seed to direct seed then to transplant. Germination rate is well over 90% for starting indoors with sweet Cherriette this year but way less in the several patches I direct seeded.
Transplants with this variety are also currently winning the race for size and early productivity vs direct seeded individuals. Despite having been severely frost damaged!
However It's also starting to look like a variety that will indeed work for direct seeding without season extension in my climate though.
I would also say in general that tough cold tolerant short season varieties are performing better than expected after being forced to resprout from the base after frost. When direct seeding having an appropriately tough variety may indeed matter!