Good Morning Mr. Rawles,
This is not necessarily directed toward the propagation and extending of tomato harvests, but geared more toward making your tomatoes better. I have found that amending the soil (pouring a quarter to a half a cup in the hole before planting) of powdered milk has a profound effect on the growth of tomatoes.
The tomatoes will grow a little shorter, significantly more stout, and have a darker green color. They even produced about the same number of flowers and tomatoes. I am sad to say that I could not do a taste test between the fruit of the two groups (non milk and milk) because a hailstorm came by and flattened the thinner non-milk tomatoes.
Better to have a hardy crop than broken stems! – Jim S.