Current production includes DIY vegetables, herbs, bedding and ornamentals totalling 12 million plants on six nursery sites.
Turnover is £8.9m.
Glendale said the plan is at "the very early stages", adding: "We've looked at several sites, that would house a new head office, which is in-line with the aims of the business which have been outlined in previous articles."
The nursery site it has been looking at is farmland belonging to Hayloft Plants.
Parkwood Group executive director Tony Hewitt said integration of Glendale Horticulture into the overall business is the aim.
In February 2016, Glendale Horticulture centralised administration, finance, logistics and distribution operations at its nursery in Fretherne.
Glendale Horticulture includes three nurseries, Coblands, RA Meredith & Son and Mahood Brothers. The company acquired Coblands in Kent in 2006, RA Meredith & Son Nurseries in Fretherne, Gloucestershire, in July 2013 and Mahood Brothers in Lathom, Lancashire, in November 2014.