We report on the cubic Ba1-xKxBiO3 and tetragonal Ba1.7K1.3Bi2O7 phases nucleation and stability in time under the electrochemical crystal growth conditions from a KOH melt. BaBiO3 single-crystal plates have been used as a seed to stimulate either oriented or epitaxial nucleation. In order to reach the maximum Ba substitution in the cubic phase crystals, a flux saturated with Bi2O3, has been selected to grow the x = 0.67 crystal, which reveals T-c similar to 4.5 K. Crystals of the tetragonal phase(a = 4.277 Angstrom, c = 21.885 Angstrom) up to some mm(3) in size have been grown at the same potential, when the Bi2O3 concentration in the flux was decreased to 9 x 10(-4) mol/KOH mole. New crystals of Ba0.9K0.2Bi0.9O3 belong to a cubic phase (a = 4.266 Angstrom), but are nonsuperconducting as first grown. The large crystals morphology, as well as magnetic properties, are discussed.