A Northland lesbian couple have been targeted by arson and had anti-gay slurs graffitied on their property, hurting their business and making them consider leaving the small town they have called home for seven years.

Juliet Leigh and Lindsay Curnow, in their mid-60s, said their sexuality had never been an issue for people at Mangawhai Heads, a seaside town about an hour's drive north of Auckland.

But police are now investigating after the pair suffered two attacks in a week, including a fire in a packing shed next to their house a week ago, the Sunday Star-Times reported.

The couple had been out to dinner, and the building exploded not long after they returned about 8pm.

The shed housed an office and equipment for their floral business, Blooming Bulbs, and the fire caused about $100,000 worth of damage, not including lost business.

"It was deliberately lit. It's a real nasty, nasty crime," Northland fire safety officer Craig Bain told the newspaper.

A week earlier, they found seven abusive messages written using a black permanent marker scrawled on their house, shed and cars.

Police believed the graffiti and arson were linked.

"I want to understand. We'd like to know it's not a local, and so would the community," Ms Curnow said.

On their business website, the couple said the Blooming Bulbs online store would not open this year as it had been the target of a "sickening arson attack".