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‘A growing machine’: Scotland looks to vertical farming to boost tree stocks

Hydroponics unit can produce saplings six times faster than it takes to grow them naturally outdoors.

It is a long way from the romance of a sun-dappled Highland glen. Picture instead a white cube equipped with the computer-controlled automation you would sooner expect to see in an Amazon or Ikea warehouse.

Scotland’s state forestry agency believes this prefabricated structure, erected at an agricultural research centre near Dundee, could play a significant part in its quest to help combat climate heating by greatly expanding the country’s forest cover.

Forestry and Land Scotland (FLS) wants to plant tens of millions of new trees in the coming years – conifers such as Norway and sitka spruce, douglas fir and Scots pine, and broadleaf varieties such as oak, alder and birch.

This white cube, held up by steel ribs and girders, can help it do so at a remarkable speed and efficiency, producing saplings six times faster than it takes to grow them naturally outdoors. In the open, it would take about 18 months to bring a tree seedling up to 40-50mm in height; in these units, that growing time is about 90 days.

“Essentially, this isn’t a building. It’s a machine; it’s a growing machine,” said Georgia Lea, a communications manager for Intelligent Growth Solutions (IGS), the Edinburgh-based firm that has designed the system.

The “vertical farm” uses hydroponics, where plants are grown indoors in very tightly controlled conditions. The type of light, temperature, humidity and nutrition can be tailored for each plant, far more so than in a greenhouse or polytunnel. “It’s better than a summer’s day. It’s totally an optimal environment,” Lea said.

In the IGS unit at the James Hutton Institute, an agricultural sciences research centre at Invergowrie, technicians use iPads to control stacks of tightly packed shelves held in a cluster of automated towers standing 9 metres tall. Robots deliver trays of seedlings to the shelves. On the underside of each shelf, rows of LED lights shine on the chillis, birch, alder, strawberries and basil on the shelf below, tuned to provide the exact spectrum of light each crop needs.

Plastic drainpipes feed in water that carries fertiliser, with doses controlled by computer. The water is harvested from Tayside’s copious rainfall, cleaned and reused in a closed-loop system. The building is entered through a pressurised airlock designed to protect its microclimate.

This particular unit covers 42 square metres and can hold eight towers, each carrying 52 trays of seedlings. In theory, that can allow FLS to grow 3m seedlings at a time, at a significantly faster pace and using a fraction of the area needed for conventional growing.

FLS, previously known as the Forestry Commission, believes Scotland would be the first country in the world where the state forester uses hydroponics for its tree stocks. It hopes the Scottish government will soon agree to approve the purchase of one of these multimillion-pound units.

After running three batches designed to prove the concept worked for trees, tweaking the “recipe” of light and nutrition to suit each species, FLS is on its sixth trial run. Many thousands of spruce, pine and broadleaves from earlier trials are now “hardening off” for years at its open-air nursery at Newton near Elgins, before being taken to the plantations carpeting parts of the Highlands.

“We came along, looked at the system and were blown away by it. It has real potential,” said Kenny Hay, FLS’s tree seed resource manager.

Until it began working with FLS, IGS had been growing pak choi, carrots, seed potatoes and herbs, alongside edible nasturtiums, marigolds and strawberry runners, as samples to show to potential buyers of its systems.

The tree trials threw up one problem: earlier batches grew too fast, leaving saplings too soft to withstand the wind once they were planted out at Newton. FLS and IGS have slowed things down, to ensure the saplings are stronger just above their roots. “We’re doing everything and anything to see what this system does,” Hay said.

These experiments have a much greater success rate than normal methods, he said. Traditionally, seeds would be scattered by machine across a nursery bed, known as broadcast sowing. Up to 50% of those seeds may fail to produce saplings. In these optimised towers, the survival rate is about 95%.

Hay predicts that if FLS buys and runs its own growing tower, it could produce up to 60% of the 24m new trees the agency needs each year – chiefly commercially planted conifers to meet the UK’s timber needs, of which 80% is currently imported.

In the Cairngorm mountains to the north of Invergowrie, conservation-minded landowners such as the National Trust for Scotland at Mar Lodge, or Anders Povlsen at Glenfeshie, are allowing their forests to regenerate slowly using naturally fallen seeds, a strategy that fits far more closely with the ethics of rewilding.

FLS feels a greater sense of urgency. The UK’s central and devolved governments have set a challenging target of planting 30,000 hectares (74,131 acres) of new forestry every year by 2025, to help meet their net zero ambitions.

The latest official data shows the UK is some way off meeting that target. Planting rates fell sharply 20 years ago, and the UK failed to restock the mature forests that had been felled.

With that in mind, Hay is delighted by the potential of vertical farming. “These are great-looking trees. I have no issues whatsoever that we can make these trees work,” he said.


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