Lawyers say police are testing the courts in their unprecedented drug bust that gardening equipment suppliers are complicit in cannabis cultivation - while botanists say indoor lighting used by cannabis cultivators has few other uses.

Police yesterday raided indoor gardening stores, including Switched On Gardener branches in Auckland and Tauranga and GreenDay Hydroponics in Mt Maunganui, swooping on 35 businesses and at least 100 homes throughout New Zealand.

Police said the businesses were a "cornerstone of the illicit cannabis cultivation industry".

Switched On Gardener's website has a banner featuring leaves with thin, green leaflets and includes a "herb's guide" to setting up a basic growroom.

Auckland barrister Andrew Speed said police would have to show the gardening shops knew that their equipment would be used to grow "illegimate herbs".

This was especially because such outfits had never been prosecuted before, Mr Speed said.

"These businesses have been operating for years and police may have thought they'd at least have a go and test it in the courts," Mr Speed said.

"These may be very difficult charges to prove."

Barrister Steve Bonnar said the charges would likely come under the Misuse of Drugs Act and hinge on proving that suppliers knew their equipment would be used to grow cannabis or that they were being reckless.

"The battle lines will be drawn on what the knowledge was," Mr Bonnar said.

The Misuse of Drugs Act section 12a states it is an offence to supply equipment knowing it "is to be used" to cultivate prohibited plants.

The offence carries a maximum penalty of seven years in jail.

Police Deputy Commissioner Rob Pope yesterday said that undercover police had had sellers give them advice on how to grow cannabis.

"Our undercover officers purchased equipment, were given advice on how to grow cannabis, and even purchased cannabis clones and other drugs over the counter from these offenders," Mr Pope said.

New Zealand Botanical Society secretary and Auckland museum botany curator Ewen Cameron said hydroponics equipment was commonly used to grow tomatoes and other produce, but indoor lighting was rarely used by gardeners.

"You would need a high return to make it worthwhile. Natural light is obviously much cheaper," Mr Cameron said.

As far as he was aware a home gardener would have no use for such lighting systems, he said.

Southern Belle Orchard owner Frans De Jong, who uses hydroponics to grow tomatoes and capsicum, said New Zealand had such strong light there would be little sense for fruit or vegetable growers to use artificial light.

"To use artificial lighting for fruit is not really economic," Mr De Jong said.

"The energy cost and of course the investment costs is not worth it."

* Misuse of Drugs Act Section 12A:

Every person commits an offence against this Act who supplies, produces, or manufactures -

(a) any equipment or material that is capable of being used in, or for, the commission of an offence against section 6(1)(b) or section 9; or

(b) any precursor substance-

knowing that the equipment, material, or substance is to be used in, or for, the commission of an offence against those provisions.

* Section 9: Cultivation of prohibited plants