Using drones to establish native plants in hard-to-reach gullies

When Chris and Sandra arrived, the farm had very little biodiversity. “There were two flax bushes at the mailbox, plus pines and pasture,” Sandra says. The rolling terrain means every paddock has gullies with waterways at the bottom which had higher concentrations of sediment from runoff. Early planting in gullies failed; grass and weeds outcompeted cheap seedlings, maintenance was hard in steep gullies, and replanting was needed. “We wanted a scalable way to establish natives without spending a small fortune, while still running a high-input dairy system through dry summers,” says Sandra.

The Campbell’s originally fenced off gullies for better farm management. These were problem spots that were hard to use, risky for stock, and increased runoff. “After fencing, we didn’t want the areas turning into long grass and gorse. We wanted to grow something useful and nice and leave something better than we found it”, says Sandra. The shift really accelerated once a trial showed drone seeding and spray management could work and be repeated across the farm.

Getting started

Sandra and Chris started with conventional planting. “Firstly, we grazed the gully, fenced it, put in cheap seedlings and then kept an eye on grass and weeds, because maintenance with a knapsack in steep gullies is punishing”, Sandra says. “After three sites and multiple replants, we looked for an easier method that would be more sustainable.”

A breakthrough came via the Otago South River Care catchment group, which had innovation funding. A trial using direct-drilled native seed (Seed NZ Natives / Bryford drill) proved the concept, and they adapted it for gullies using drone seeding and repeated selective blanket spraying to suppress competition. Botanists (Red Tree Consultants) helped with drone seeding technique and fast-establishing species in the early phase. As drone services became locally available, costs dropped from thousands per visit to a few hundred per gully, making the system practical year-to-year.

Sandra and Chris moved away from traditional planting with spot maintenance toward a repeatable recipe: graze → Roundup → seed → plant → broadcast selective spray about three times per year to keep competition down while natives establish.

"We learned that missing a spray can undo progress, and that broad spraying over a tolerant species mix is far easier than spot spraying,” says Sandra. "We also stopped using plant protectors because broad spraying reduces grass pressure, protectors add major labour cost, and we haven’t had much browsing damage from rabbits; and as sites mature, we stop broad spraying and add taller tree species like ribbonwood where needed to provide shade and structure.”

Challenges along the way

Some gullies still contain problem tree weeds such as pines, broom, and blackberry, which require manual work with a knapsack or extra funding to manage. The spray-tolerant recipe also limits which species can be used in the early stages, with more sensitive plants such as ribbonwood, toetoe, and kōwhai often needing to be added later for height and structure. Even with visible results, getting others to try the approach has been harder than expected.

What’s next

"We’ll keep rolling through our annual gully programme, adding another gully each year, connecting up plantings, and tackling weedy gullies differently - potentially using EcoFund support for knapsack work,” says Sandra.

"We also want to add more tall tree species to increase shade and long-term structure, deal with lingering issues like willows in older wet areas and refine our carbon/offset mapping as plantings expand and Douglas fir blocks are replanted and begin counting in our farm’s offset position.”