Aren't there different varieties? I have the varied pink shades that reseed themselves and they get over 2 feet tall, and then some.

Mine six feet. Not the usual; and they do not achieve it in one year.

There are two general categories : tall and not. The former gets butterfiles. The latter is known not to get butterfiles; my experience as well.

Does feeding well a "not tall" category pentas increase it's height size dramatically?

Food does not alter the genetics.

A little off topic, but I bought a red one from Lowe's death rack last year hoping it was a tall one. I have it in a pot, and one side of it died, but the other side is going strong. If it was upright, it would be about 2 feet tall, and it's still growing in a 1 gallon pot. I saw a monarch going crazy on it the other day, so I'm letting it go to seed, because someone told me that the dwarf red hybrids will revert to the tall ones when grown from seed. He also said that sometimes, if you take cuttings of the dwarf red, they'll also grow tall, so I'm doing that too.

As to how tall mine are, the purple one is in a 3-gallon pot and only got about 18 inches tall, but then, I didn't fertilize it like I should have, just gave it 14-14-14 timed release pellets.

All of it was on topic.

View the root+medium ball of the 1gal plant, to see whether it could benefit from 3gal.

For how long has the second-mentioned plant been in 3gal?

Mine do not and never have produced seeds. In ground for years. Could it be that your information source was assuming that the broadly true information applied to Pentas?

Lukas Nursery (Oviedo) routinely gets Pentas of the tall kind. Today I asked whether they ship: No.

Irma, if you hit a dead end in your further attempts to get Pentas, then ask me to get some from Lukas and ship them to you. Better than cuttings of mine, because mine are not reliable rooters, and the successful ones do not always become vigorous plants.

What colors does Lucas carry, Four? The most common are the red ones. They are excellent, but so are the others. It's looks good to space the red with the pink and the white and...I have had different pentas for many years and none of them have ever produced seeds. They are very easy to grow from cuttings, however.

Edna told me that the tall ones there are labeled "Ruby". I did not look at any, but will remember to do so.

Clipped from a random photo of it on the Web :

Yes. They are the ones we call "red." They are the most common tall varieties that nurseries get. They are excellent for butterflies and good for hummingbirds and other pollinators.

This leads me to a question, why is it that most pentas don't put out seeds, but still produce a good amount of nectar which is designed by plants to lure pollinators so that their pollen can be transferred to other plants in order to produce seeds?

A native plant would perform according to Nature's design. Very many commercial plants are varieties that have been bred, many though several iterations, for certain characteristics, and sometimes intentionally to be sterile.