While neither party would comment, Horticulture Week believes a deal could be struck by the end of the year.
Roundstone, which hosts GroSouth on 12 November, is based in Chichester, West Sussex and began growing plants commercially in 1985. The Kahn family are owners and Peter Cook, who recently left the HTA board, runs the business.
The grower produces bedding for B&Q among others from 29ha of glass, with 150m plants a year being grown.
Warwickshire-based The Newey Group, which includes Young Plants, is run by HTA seasonal plants group chairman Alex Newey.