Shortlisted were Crowders, Johnsons of Whixley, who have said they have not won, and a consortium of Hillier with Wyevale Nurseries and Oakover. Hillier and Wyevale say they have not heard anything.
The Cabinet Office, Department of Transport and HS2 are due to announce the award the £5.8m tree and shrub contract for the £50bn scheme this autumn.
Construction work on the first phase of the rail link is set to begin in 2017 and work is expected to be completed in 2033.
Growers say HS2 requires more than one million native trees and shrubs for phase one in 2017. Among the one million plants there are only 340 trees taller than the required 3m but 80,000 plants higher than 1m.
HS2 said: "We expect to make an announcement about the plant materials contract reasonably soon."