Now, the organisation is supporting the use of 1080 to control the introduced animal pests that it says are wreaking havoc on the country's unique biodiversity.
"In the 1980s this country was on the point of losing its pōhutukawa trees, our unique, native New Zealand Christmas tree, and one of the major causes of this impending environmental disaster was the possum. Project Crimson was created to protect and restore (them)," she said.
"Sadly, pōhutukawa and rātā are irresistible to possums. It's estimated that New Zealand's possum population consumes around 20,000 tonnes of foliage a night from our forests. (Source: Predator Free NZ Trust, Landcare Research). That's equal to about 454 fully-laden logging trucks every single night.
"Possums browse on newly expanding flower and vegetative buds, causing rapid canopy dieback. Severe defoliation over just two years can cause the death of large old pōhutukawa and rātā, and has resulted in the loss of these species from large areas of New Zealand's native forest.
"In one part of the Ruahine Forest possums took less than 10 years to reduce the proportion of rātā and kamahi in the forest canopy from 74 per cent to eight per cent."
Project Crimson had extended its advocacy to cover all New Zealand native tree species through its Trees That Count and TREEmendous initiatives, but its initial focus on pōhutukawa and rātā provided a 30-year model for how to support native forests as a whole. Project Crimson trustee (and celebrated entomologist) Ruud Kleinpaste agreed.
"In the early days of Project Crimson, the closest thing we had to a silver bullet was 1080, and it was the biggest single factor in the effort to halt the decline in our pōhutukawa trees, as well as our equally spectacular red-flowering rātā trees," he said.
"Conservation of pōhutukawa and rātā is not just about protecting the trees. It also concerns all the other associated species, such as the birds that pollinate the trees and the invertebrates that recycle the nutrients.
"Introduced mammals are the biggest risk to our indigenous flora and fauna. Poison is a blunt tool, and while I look forward to New Zealand finding other methods, it's currently the best tool we have to control pests in large landscape areas.
"Without 1080, I doubt whether we would still be enjoying the annual display that lights up our coastline and is such a prominent and loved feature of a typical New Zealand summer.
"Prior to a 1990 possum eradication programme using 1080, Rangitoto Island's pōhutukawa forest was under attack and dying. Rangitoto is now a blaze of healthy pōhutukawa, flowering throughout the summer.
Rātā and fuchsia were also flourishing in the Ōtira valley (Arthur's Pass) after 30 years of 1080 drops. Ten kilometres away, in the Arahura Valley, where 1080 was not used, rātā skeletons were abundant.
Ms Fitzpatrick said it was only protecting the native forest that enabled the continued proliferation of tūī, kererū, korimako/bellbirds and other species.
"It's the native trees that provide the habitat for our native bird taonga, and that's where the real value lies in the use of 1080," she said.
"That was the choice we made nearly 30 years ago when we were staring down the barrel of losing our pōhutukawa and rātā, and I'm sure it's the choice most of us would support now."