Growers of bedding plants use a growth regulator to control height in their plants. They do this so the plants don't get leggy. Most likely the bedding plants you purchased were already in bloom at time of purchase. Sad to say that all the pinching in the world is not going to encourage them to grow taller.

Cutflower growers purchase either plugs or seeds through wholesale brokers. These plants or seeds are specifically for cutflower production.

In the past I have seen 'Rocket' snapdragon and 'State Fair' zinnia for sale at a small local nursery. And, it is also possible to find some nice sunflower seeds to grow as cuts.

Since cutflower plants are not readily available at the retail level to the general public, this year we are taking plants of some of the cutflowers we grow to the farmers markets. We hope to encourage some of our customers to grow a few in their gardens.