Newspan provided the structure, with Geo Hodges the building contractor. The building is 1,600sq m, including a 380sq m learning zone.
Managing director David Little said the learning zone is a "classroom in the country" for 100 school children. The centre has an existing nature reserve and the classroom will provide an area to study ecology and other areas of education.
Little said he had now recovered from an aggravated burglary at his home (HW 26 March) but had installed more security measures at home and work.
HTA security advisor Jeremy Davies said: "While violent crime is rare, it is on the increase because criminals are more desperate. They are searching for easier targets such as garden centres. Poplars has contacted the HTA for security advice. I have subsequently visited Poplars and reviewed its existing security measures and advised on new cash-handling methods.
"I would advise all garden centre and nursery owners to review their own methods of cash-handling and security measures for protecting stock from customer theft and preventing burglaries."