The Horticultural Trades and Garden Centre Associations are to share premises at Theale, Reading, from February 1, 2013.
Both associations say they are keen to develop closer working links and are "looking forward to sharing premises again." The GCA was originally formed within the HTA in 1966, and became independent of the association in 1979.
HTA director general Carol Paris said: "HTA and GCA have been discussing this move for some time. It is important that both organisations retain their individuality yet have the opportunity to work more closely together on issues affecting the industry. It will be much easier to do this when we are sharing offices."
Peter Burks, GCA Chairman, said he shared Carol's enthusiasm for the organisations to collaborate more whilst serving the needs of their individual members.
"Both myself and Carol are committed to the various parts of our industry working together to make it stronger, more vibrant and prosperous," he added. "There is no benefit in duplicating effort and working from one office will enable us to more readily determine and address the unique needs of our members."