Jujubes

We planted a Jujube (Ziziphus jujuba) about 5 years ago.  It looked like a twig when it was planted and I'd have to say its growth has been disappointing. It's still not much more than 30cm high!  Jujube bushes are supposed to grow to 5 to 12 metres but I can't see that ours will ever reach anything like that height despite it being in a sunny aspect with plenty of water (they're supposed to be drought hardy and not need much water) and fertilised regularly (they're supposed to not need much fertiliser!).  So it's a puzzle to me.  Perhaps it's just a one-off plant that refuses to grow very much.  In any case it has finally produced some fruit and the results are quite tasty, better straight off the bush, in my opinion, than dried ones.