It has been the first commandment for contestants competing on The Block: No help from outside designers.

Every design and styling decision has to be made by the contestants, and it was a rule that got Sara into trouble in the early weeks of the competition, when she sought help from a wallpaper designer in the creation of her room.

So, given every team is expected to adhere to this stringent rule, it might strike the viewer as odd, that come terrace week, almost every team is consulting a landscape designer in the production of their outdoor space.

But according to the show’s executive producer Julian Cress, there’s a marked difference between hiring an interior designer and hiring a landscape designer, and for that very reason, contestants are encouraged to employ a landscaper during terrace week.

“A landscape designer is very much like a builder, in my view, someone whose skillset is way beyond just design,” he explains.

“To execute a successful terrace is a building project, and it’s beyond the ability of our contestants to execute alone. This is why they’re allowed to bring in a landscape designer to help.”

Cress says the role of a landscape designer transcends that of an interior designer.

Related: View the five Gatwick apartments for sale

“It’s far more technical than just choosing plants. A landscape designer has to consider things like drainage, so it’s a much more complicated process than just design.

“Elyse and Josh put a pool [in their backyard] last year, and there’s no way any of our contestants could build a swimming pool. In fact, they’re not allowed to. Only a registered pool builder can do that.”

Cress added that he wasn’t concerned about the contestants circumventing the rulebook by hiring a landscape designer who could dabble in some interior design.

“Never in my experience or travels have I met a landscape designer who is any good at interior design. I certainly wouldn’t let them choose a sofa for my living room,” he says.

“We don’t help any contestant make any choices regarding the [tradespeople] they work with, it’s up to them to find the best one they can. There’s lots of competition to secure the services of someone like Dave Franklin, because he keeps winning the award for best landscaper in the country.”

With room reveals only days away, Cress reiterates the message of the week – that the competition for grandest terrace is coming down to a battle of budgets.

“With this project, some of the contestants have closed terraces some have open terraces, some have full size garden areas and others don’t,” Cress explains.

”The challenge of setting up these spaces in a competition was particularly difficult. Usually terrace week becomes a competition between who has managed their budget better. When you get to the pointy end, you see who has run out of money, and its obvious then when they present their space.”