The project is being rolled out next year, said director of sustainability Chris Harrop, who insisted the service did not aim to replace garden designers.
"We want to help our members turn design into a buildable project," he said. "Landscapers are good at installing products and at visualising what an idea actually looks like.
"But putting that creativity on paper and calculating quantities may not be one of their strong cards. We are not taking creativity away - this is about buildability."
Harrop also said Marshalls was expanding its geographical horizons in a joint venture with its Belgium arm, Marshalls NV. It will look at ranges for Benelux countries, as "a key part of our strategy going forward", he said.
His company was expanding its Fairstone range by sourcing stone from China as well as India, he said. This raised complex sustainability issues.
"It's hard for one company to change the culture, habits and industry norms in a country as big as China, especially where 90 per cent of the products are for the internal market.
"But issues of sustainability can be solved not by money, but will and perseverance. Having a properly-accredited supply chain offers more volume and sales thanks to demand from ethically-minded consumers."
Marshalls has also recently launched a new coated-concrete product from its Active Shield range. It claims that the surface will not stain if you spill oil or wine on it.
See interview, page 17.