Marshall told Horticulture Week that feedback showed customers had grown disillusioned with Tesco-owned Dobbies, which Midlothian Capital bought for £217 million in summer 2016. Chairman Andrew Bracey appointed Marshall as chief executive this spring.
He wants to target AB demographic customers and said demographics had slipped to C1 and 2's under Tesco. Customers said ranges lacked inspiration and were unexceptional and they reminisced about the days when Dobbies offered knowledgeable gardening service.
Dobbies will go 25% good, 50% better, 25% best, away from 5% best and 70% good.
Work will start in January, beginning at the stores which are easiest to get planning permission for.
Dobbies also has separate money for acquisitions and is currently looking at buying two south east centres.
IT will have new systems allowing better communication between Dobbies' 35 centres. There will be an online stock ordering system, business information tools, new till software and hardware and integrated systems. Online with Ocado will start in March 2018.
The board approved the moves two weeks ago and managers met at Edinburgh and Milton Keynes to hear the plans. Regional managers have detailed them to every member of staff, in information-sharing steps which Marshall says are unprecedented for a retailer.
Marcus Eyles, the new head of horticulture, is charged with doubling plant sales in the next three years. Plantaria managers are now in charge of stock control, deciding which plants aren't good enough to sell. Money will be spent opening up planterias. British-grown plants are a focus. Stihl battery tools will be introduced.
The pink geranium Dobbies logo will go.
Marshall said "shops looked dreadful" but he has already started to change that with new autumn and Christmas ranges. He said Dobbies had missed millions in autumn by going into Christmas in July.
He said the store "architecture was more like a DIY" and he will bring plant and gardening back to the fore.
Marshall said because many of his new staff used to work for him at Wyevale, they knew what he wanted so changes could happen quickly.
Restaurants will have food to go and local, fresh and homemade food. Bakeries will go into farm shops. There will be more butchers and greengrocers.
Concession income is planned to double to £12m.
Health and safety comes under former store manager Ross Anderson.
Training and e-learning is under Pippa Hawkins.