Could be a number of factors... do you have them in the same conditions as before?

I don’t grow tiger lilies, but I do grow other types of lilies.... I find them a bit picky about their conditions lol. I find they like loose sandy non-alkaline soil, even moisture (moist in the summer, and not too wet in the spring or winter so they don’t rot), lots of sunlight, plenty of fertilizer, and not to be planted too deep, but deep enough so they are protected from the cold.

Yes, same conditions, I just dug them up, separated them, respected and replanted. Can’t say for sure about the depth.

Do you think if they were too deep that would restrict their height?

Too deep could have negative impacts. Tiger lilies are really good at pulling themselves down to a desired depth but can't dig themselves out if too deep. Plant a bit shallower in late fall and let them do their thing.

You don't have the bright red lily beetle in your area yet, do you? That would also result in smaller and smaller plants every year. You'd see the damage (& the beetles) though.

I don't think I have the bright red beetle, ugh. I have heard people call just about any lily with spots 'tiger lily'. The ones I have remind me of the ones that we had when I was a kid. Bright orange with lots of spots. I just measured, the tallest is 16 inches, with most of them being 12/14 in, with quite a few 6/8 inches. I remember the ones one the farm being taller....perhaps I was just shorter....lol

Tigers actually have recurved petals. Mine are about 16-18" high. They haven't increased at all but i think it's because they're in a spot that might not get enough sun for them.

Marciaz3 are you saying these are not tiger lilies? It would not be the first time a plant was sold under the wrong name. lol

They look like an Asiatic lily to me.

These are my Tigers (taken last August):

Yours look like Martagons to me, I have some lovely yellow ones, citronelle lillium, 3' and some very deep red ones 2', just like those.

My Martagons are much smaller - the flowers, that is:

Thank you for the name clarification, my question is in regard to their growth. I several other varieties of Asiatics which have done well, multiplied and continue to grow tall. the only difference is these orange ones were dug up and replanted. As Smivies suggested I probably planted too deep.

So, I think I will try to dig up and replant. thank you.