Good question, I would like to know myself. Also would like to know if a stressed tomaot plant looses all of its buds and recovers, will new buds form? Or is it a 1 shot deal?

I hope the experts chime in, but here are my random thoughts. It's probably a combination of factors, which may be variety related. I used to think that being a bit pot-bound before planting out would stress the seedlings into thinking growth was done and so forming blossoms for reproduction. And it probably does, for some varieties. But then, there's my itty bitty Micro-Tom, only about two inches high, on it's third set of leaves and has never been close to pot-bound. I see there is one blossom bud starting to form. I also see blossoms form on Stupice seedlings sooner than on later varieties started at the same time. So earliness of DTM also seems to be a trigger. So it's possible that with early cool season varieties, the first blossoms come automatically after about the third set of leaves? Or maybe they do that with all tomatoes?

It would be interesting for someone in a tropical zone, to compare the flowering time of identical seeds started in the ground, as opposed to those started in pots and allowed to get a little pot-bound.

Good question, now I will have to keep track of all my varieties and count the leaf sets at first blossom!

I think I remember reading somewhere that once the plant has a certain number of leaves, it produces too much sugar via photosynthesis so it knows it's time to put the extra energy into reproducing.

Without doing some background research I don't know what specific molecular events have to happen such that a plant switches from the early phase of initial vegetative growth, stems and roots and foliage, to the sexual stage of blossom formation and fruit set.

Perhaps someone will come along and knows that already or wants to do the Goolging that might be required.

Carolyn

Catman hit on the factor, number of leaves (nodes) produced. Number of leaves varies by variety. Expressions of hormones (auxin, GA and to some degree cytokinins) are what starts the process. The hormone levels build as more root tips and growing points are produced. I think I have this part right - growing points produce auxins which stimulate root tips and root tips produce GA which stimulates growing points. As more are formed the plant has more hormones.

There are environmental factors which effect flowering. Some varieties can be inhibited by daylength (24hr cycles from lamps). Also certain applications of growth regulators (hormones) can alter flower development.

mulio, re this:
Some varieties can be inhibited by daylength (24hr cycles from lamps)

Does this translate into slower blossoming for geographical areas that have long summer daylight periods, like Alaska and really northern areas?

If it did it would be the exception.

These daylength mentions were exceptions noted in the CRC Handbook of Flowering. It did not state the varieties but rather the observation that in glasshouses certain lines with nearby lamps or outside lamps were inhibited.

It may be the case that if some genetic material from wild species native to equatoral regions were introduced to make a line (for say disease resistance genes) there may have been some daylength sensitivity carry over into the germplasm.

(L. cheesmanii, L. chilense, L. hirsutum, outcrossing selections of L. pimpinellifolium, S. juglandifolium, S. lycopersicoides, S. ochranthum, and S. sitiens are all short day species)

Yea...what catman said is right or close to right, I believe. I think once a tomato plant has a certain # of leaf sets/branches, it will then grow the ones with the blossons on them. Ever notice that first bud set is right in the middle of a V to two new branches (sometimes 3 or 4)? If there's a way to differentiate those branches to the others below it, or maybe take a count of several plants to see how many branches they get before the first blosson set appears, I imagine that would be the most accurate method that I can think of regarding when a tomato plant will blossom.

Isn't is the same as when the temperature gets hot enough, the clothes comes off and you are ready to mate ? sorry, couldn't resist ;-).

lol...funny