Frozen trees help extend planting season

Forestry and Land Scotland (FLS) is trialling frozen tree planting across Highland Perthshire and the Angus Glens as part of exploring ways to extend its planting season.

The young trees are frozen and stored at FLS’ Newton Nursery before being transported to the planting site. Here they are left to thaw under controlled conditions before being planted.  

Freezing young trees increases dormancy time - so they don’t use any nutrient reserves for growth – and allows them to be planted after the recognised winter planting season of October to March. Additionally, the low temperature makes the plants less susceptible to mould, disease or pest damage.  

While using frozen trees is not common practice in Scotland, it is a technique deployed in Canada where FLS Stewardship Forester Paige Klinkman originally hails from

Paige said:

“Freezing the trees puts them into dormancy as they would be in winter ensuring they last longer. The cells of a frozen tree have enough locked-in nutrient reserves to survive once planted, even in warmer weather.

“Planting trees when they are dormant, typically in the colder months, allows trees to focus energy on developing root systems rather than producing leaves and shoots.

“The frozen plants also don’t have the same issues with mould or plant shock which is when the roots are damaged during transportation and distribution across sites.”

The frozen trees are planted in the same way as any other bare root or cell grown tree, with the thawing out process the only additional step. A slow thaw is needed and temperatures are kept low (around 5 degrees Celsius) using silvicultural tarps.

The trials using a mixture of noble fir, Scots pine, Sitka spruce and mix broadleaves have highlighted the benefits that the use of frozen trees in can bring to FLS forestry practices. 

Paige explained:

“This method means we have fresh trees later in the season which is hard to get if not frozen. Being planted at the start of summer provided the conditions that allowed the trees to establish themselves more quickly ad become hardier.

“Other benefits were that the young trees had limited exposure to deer damage with a wider variety of grazing options available to deer in the warmer conditions.”

As climate change throws new challenges at forests including rising temperatures, prolonged drought, increased pests, along with the need to grow more timber and faster, innovation is key to helping ensure security of future timber supply for Scotland’s thriving £1-billion forestry industry and sustain forestry’s contribution to the wider economy. 

Trialling methods such as frozen seedling stock is part of FLS’ endeavour to plant more trees, so that forests and woodlands contribute significantly to tackling the climate emergency and continue to support jobs, businesses and livelihoods in Scotland’s rural communities. 

Notes to editors

1. Forestry and Land Scotland (FLS) manages forests and land owned by Scottish Ministers in a way that supports and enables economically sustainable forestry; conserves and enhances the environment; delivers benefits for people and nature; and supports Scottish Ministers in their stewardship of Scotland's national forests and land.
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3. Media enquiries to Neil Ratley, Media Manager, Forestry and Land Scotland Media Office 07748 872785 or neil.ratley@forestryandland.gov.scot