The NHS Forest sources its trees from tree nurseries, but what exactly do they do and why?
Tree nursery vs. natural?
Trees are capable of reproducing without human intervention but have been intentionally grown and planted since time immemorial. Anthropogenic planting, intentional planting by people, may be beneficial or even necessary in areas with no pre-existing tree cover or where the conditions for natural regeneration are unfavourable. It can also be used to accelerate establishment rates and to achieve particular planting outcomes. British tree nurseries collectively produce millions of trees each year that have been professionally grown to a high standard in a biosecure setting. For the most part NHS Forest tree orders are distributed straight from the nurseries to recipient healthcare sites.
Seed collections
Native trees supplied by NHS Forest are grown from indigenous seed collected all around the UK. Seed collections may come from sources or stands (groups of parent trees within a specific geographical area) or be obtained from a seed orchard (a plantation specifically designed and managed to facilitate seed harvesting).
Collections are undertaken during the late summer and autumn months, during or just before natural seedfall. Most domestically sourced seed is gathered by professional collectors and transferred to a seed house for processing and treatment; some nurseries undertake in-house seed collections for their own use.
Fruit tree grafting
Unlike native trees, productive fruit cultivars cannot be grown true to type from seed and must be grafted together using component parts from closely related species. Grafts comprise two parts: a rootstock at the base, and scion wood that will become the upper fruiting section.
Grafting is normally undertaken in early spring and the trees grown on over at least one subsequent growing season to allow the union to form between rootstock and scion wood and for the tree to reach a given size.
Production methods
Nurseries are horticultural operations that propagate and cultivate young plants for transplantation; forest tree nurseries specialise in trees and woody shrubs and collectively produce millions of trees each year to a diverse range of specifications. They are commonly differentiated by their production systems:
- Bare-root or field grown production is the more traditional nursery practice. Seed is sown directly into the ground, and the germinated trees are dug up when they have achieved a desired size. This stock is then supplied without soil or compost around the roots – hence the name.
- Containerised production refers to trees grown in trays or pots of compost. Cell grown trees are produced in small tube-like containers and supplied with root systems enclosed in plugs of compost; larger stock may be delivered in a disposable pot that should be removed prior to planting.
NHS Forest supplies both cell grown and bare-rooted trees. If you would like to read more about the rationale for selecting one or other type of stock, you can find an overview of our tree procurement strategy on the NHS Forest website.
Seed sowing
Once the seed has been treated and distributed to the nurseries it will be sown and exposed to the right environmental conditions (adequate moisture and temperature) in order to germinate into new trees. Seed sowing timings vary – some species must be planted soon after collection in the autumn, others will be sown in the spring – but all seed is batched by origin to ensure that the provenance can be traced back to source.
Seeds may be sown into containers of compost or directly into the ground in a field seedbed depending on the type of productive, and tree nurseries may utilise specialist equipment to handle seeds of differing sizes and shapes, or sow by hand.
Growing trees
Newly germinated seedlings require lots of proactive care and attention to ensure they are able to develop into viable trees. Nurseries are carefully controlled environments where routine irrigation, weed control, fertilisation, regular monitoring for pests and diseases and quality control checks can be undertaken to ensure that healthy trees are supplied for planting.
Every tree will need to spend at least one growing season (March – September) at the nursery before it is ready to be supplied. Some larger or slower growing trees may be grown on over multiple years to achieve a given size. A strong, healthy root system will maximise the chances of a tree successfully establishing when planted out. The nursery may thin out stock to remove smaller plants, or replant into larger containers or more widely spaced seedbeds to allow additional space for the roots to develop.
Lifting and grading
Once the trees are ready for planting it must be lifted. In a bare-root nursery, trees are dug up while dormant (i.e. during the winter months) and supplied without soil or compost around their roots; cell grown trees are removed from their cells leaving individual root systems enclosed in plugs of compost. Stock is then graded into single species batches of uniform size and wrapped or bagged to protect the roots and retain moisture in transit. Grading is also a final opportunity for further refinement and culling of abnormal stock.
Packaging orders
The final stage of the process sees tree orders prepared for dispatch via courier delivery networks along with any planting sundries. Smaller consignments are packed in cardboard boxes; larger orders may be sent on pallets.
Feeling inspired?
Hopefully this look at how trees are produced has left you wanting to plant on your healthcare site. Please visit the NHS Forest website to find out more and apply.