He said another GCA centre is due to change hands imminently, with three centres altogether likely to be sold this autumn, including one to Blue Diamond.
Grosvenor also remains a GCA members after being bought by Blue Diamond in 2012.
Armitage said 2015 prospects depend on the weather and "if goes to plan" he hopes gardening sales will take centre stage, and if we will "fall back on other elements".
He said at his own centres we are "guarding against fluctuations" by developing catering but at his Birchencliffe centre a new outdoor covered area has weatherproofed plant sales.
Armitage said early bedding plugs suffered this year but sees growth in planted containers and instant colour continuing in 2015.