So, this is one of 3 threads I have going on pruning (the others are on ground cherries and currant tomatoes). As I said in my original post, this is my first year pruning, and I've gotten pretty comfortable at this point with the indeterminate plants as far as recognizing suckers; I have them all pruned to the "strong Y" (double leader).

I decided to try something different with each of my 3 Maglia Rosa. One I would just leave alone. One I would prune to a double leader, and the other I would do something in-between (I think I decided 5 leaders, based on the way it was growing). But I'm kind of stumped on what's happening with the one I pruned to two leaders. I'm not sure I really understand the difference between the indeterminate and semi-determinate growth pattern, I remember finding a thread at that other tomato forum and there were a lot of technical terms that I didn't understand.

Anyway, the main stem kind of petered out into a leaf branch, but not before having 2 flower clusters in a row. I had let the last sucker grow because it looked like the main stem. If you look at the bottom of the picture, that's the main stem going out to the left, with 2 flower clusters...but it has no growing tip...it's just is a leaf branch, that just ends. As you can see the sucker on the right has grown up, has a flower cluster, and also ends in a leaf branch on the right, while it's got a sucker and a leaf branch to the left.

So is this the difference between indeterminate and semi-determinate? That the semi-determinate instead of having a growing tip, gets to a certain height and then only grows more through suckers?

I am not sure there is one accepted definition of semi determinate. It seems more like seed company sales talk to me, but maybe other people here have a better answer.

My money is on the maglia rosa that you did not prune at all. That variety does well with no pruning.

Cole_Robbie wrote: ↑Tue Jun 16, 2020 3:40 pm I am not sure there is one accepted definition of semi determinate. It seems more like seed company sales talk to me, but maybe other people here have a better answer.

So as I think I stated earlier in this thread I believe I had found a semi-determinate discussion on that other forum, but I didn't understand it at the time. Anyway, it seems like my Maglia Rosa stems go some number of nodes, if that's the right word, before they just terminate into a leaf branch. However the sucker below the termination keeps growing, and presumably it will go the same number of nodes (I guess) before terminating into a leaf branch, but then of course it will have it's own suckers.

So it would seem you can get a semi-determinate like this to "vine up" as long as you are careful not to remove that last sucker, otherwise you will terminate that stem.

Cole_Robbie wrote: ↑Tue Jun 16, 2020 3:40 pmMy money is on the maglia rosa that you did not prune at all. That variety does well with no pruning.

Right now the one that I haven't pruned doesn't have any fruit yet to speak of, while the other two do. Little different location and planter, so not a 100% reliable comparison, and of course it may change over the season.

I agree that there is no one accepted definition.

Indeterminates have repeating growth habit: three leaves, flower, three leaves, flower, etc.

Determinates are because of ’self-pruning’ gene: they typically end growing hight soon after the first inflorescence. Many have 2-3 inflorescences and one or two leaves between in the main stem. The appearence of the first inflorescence depends both on the variety and growing conditions. Cold nights at the time of the first true leave grows leads to earlier flowering (and shorter plants).

Then there are also the so-called ’suppressor of self-pruning’ genes, such as sft. They delay the appearance of the first inflorescence, and cause more leaves between them before the hight growth ends. Maybe they can also do what you describe above on the MR growth habbit. I think these are the semi determinates. These plants are taller but you can recognize them by not having the standard three leaves between inflorescences.

If you cross indeterminate and determinate, F1 will be indeterminate. But if you cross semi determinate (potentially misclassified as indeterminate) and determinate, the F1 will be determinate (i.e. a shorter plant than one of the parents - assuming the sp suppressor is a recessive gene). This happened to me with Justyna which is classified as indet by Tatiana (http://tatianastomatobase.com/wiki/Justyna). Or maybe I just had a spontanyous mutant. I also have a MR x det cross growing this year: it has more compact growth habbit than MR but is larger than the other parent (which may carry some type of dwarf gene - not the dwarf tomato project one).