Last year I planted a Lemonade, a Lemon, a Tangelo and a Lime. The Lemonade and Lemon are doing very well, the Tangelo and Lime seem to have stagnated. Both of them look healthy enough, they just don't seem to have progressed, no flower or fruit. They were in pots for a few years, could this be the problem? Is there anything I can do to get them going?