Two dozen landscapers and gardeners gained the newly minted level 2 diploma in work-based horticulture from City & Guilds.
"Staff based in Essex showed a high level of skill and knowledge in commercial landscaping environments," said business manager Mark Wells.
"Having workplace tests was fundamental to the success of this scheme, enabling them to be tested in a familiar environment."
Pinnacle PSG worked with training provider On-site Training UK. Assessor Nigel White said candidates had good plant knowledge and sound work technique.
The firm wants more staff to pass the qualifications over the next year and is putting one of its managers through an NVQ level 4.
Pinnacle PSG employs more than 1,700 people from 32 offices nationwide and turned over in excess of £40m last year.