I have grown roses from seed for about 3 years, basically they are chance seedlings I find scattered around the yard from my various rose plants. I have had some for 3 years, and most are only 12 inches or less and none have ever flowered! I have at least 10 seedlings, all have been doing horrible. The strangest part is I left 2 to grow wild, and they are a little bigger than my potted seedlings, and even the wild ones never got flowers.
I have mine in a large pot with miracle grow potting soil and extra perlite for drainage. Under a tree they do better but grow terribly slow, in more sun the leaves seem to bake and almost no growth, no matter what I do they are hardly growing and I am flowerless. They are a single stem growing straight up. They usually sprout around March-April, and growth continues to about early November, so plenty of time to get big and get first flowers, but 3 years, something is wrong!