Ripe Vegies/Fruits emit a hormone that either stunts or aids other fruits/vegies nearby to start to form. Possibly not enough ripe ones to aid the others along; or that that one tomato is releasing a 'stunt' hormone to prevent the others from ripening. Also proper fertilizing (not regular fert, but fert especially for tomatoes) will help.
100% correct. Scotts makes a good "late-season" commercial fertilizer that I use but you have to have a wholesale connection to get it.
Every fertilizer has a three-number code on the front indicating the amount of nitrogen (N), phosphorus (P) and potassium (K) in that order. Plant growth, and to some extent fruit development needs high N, where ripening needs almost no N and a higher P and K. These are only three of the nutrients plants need but they are widely considered to be the primary three.
Also, many plant, including tomatoes, will change their hormonal balance due to stress - colder weather, no rain etc and accelerate the ripening process to ensure the production of seeds. I always cut back on the amount of water my tomatoes get three weeks before the first expected freeze.
You also need to know if the strain (variety) has a
determinant or an indeterminate growth habit.
If canning and I want them all to ripen at once, I select a determinant variety to get enough to ripen at one time. For table varieties, I prefer an indeterminate variety so that we get a few tomatoes at a time all summer long.
