Part 1: Selecting and planting trees in small spaces
At NHS Forest we get a lot of queries about planting trees in small spaces. How much space is really needed for trees to establish without damaging adjacent buildings or paved areas? Which species are best suited in a compact space? In this blog we will reveal the answers to these questions and more!
Looking for information about care and maintenance of trees in small spaces? Read part two of this blog. If you already want to register for fully funded trees for your healthcare site, visit our tree planting pages.
Big tree, little tree
Thinking about trees, we instinctively picture larger ones – and with good reason. Mature trees are often the predominant natural features in our landscapes. Some are true giants with the largest ash, beech, lime and oak trees able to exceed 40 metres / 130 feet.
At NHS Forest we advocate a principle of ‘the right tree in the right place’. We love tall trees but appreciate that many healthcare settings simply will not have the space available to accommodate larger growing species and may only be able to accommodate a small number of trees overall. When planting trees in small spaces, the choice of species matters.
Strategic planting
Planting trees in small spaces can have both positive and negative impacts. Yes, they start off small and we know it is easy to get caught up in the excitement of planting – but a little sapling will grow significantly, both upwards and outwards. Using species that may become too big for the available space is a recipe for future issues, requiring time and money to resolve that could have been better assigned elsewhere.
The solution is to plant strategically, giving careful thought to the location and the specific trees you are planting before anyone puts a spade in the ground. Consider whether there are any buildings, paved areas, overhead wires or underground services such as pipes or cables adjacent to the site. Is it likely that a mature tree would cause an obstruction? Is there any doubt about maintaining the trees in five, 10 or even 50 years’ time?
If the answer to any of these questions is ‘yes’, it may be best to exclude these areas from consideration for planting, or to seek professional advice from an arboriculturist before planting.
How much space?
Trees have the potential to cause structural damage so it’s important to consider both the potential height and the extent of the canopy as a mature tree. As a general rule it is a bad idea to plant trees any closer than a distance equivalent to the mature height of the tree from any buildings or infrastructure, and we would suggest an absolute minimum distance from buildings of 5 metres regardless of species.
Tree roots can grow far beyond the width of the canopy – up to three times the height of the tree – but are unlikely to penetrate the foundations of modern buildings. Neither are they strong enough to physically move buildings around by themselves. However, the roots of mature trees can cause subsidence and structural damage due to soil shrinkage, particularly in very dry years and for buildings constructed before 1950. They may also block drains or lift paving.
Avoid planting under existing trees. The larger canopies may cast shade and more established root systems will be at an advantage in competition for groundwater. This will restrict the growth of the younger trees.
10 trees under 10 metres
Carefully considering species is essential when planting trees in space spaces. Here is NHS Forest’s guide to some of the UK’s more diminutive native trees, all under 10 metres tall at maturity. We’ve also included a few woody shrubs such as hawthorn and dogwood that are excellent both for shelter planting and promoting biodiversity. Many of these species are available through our tree bundles.
 | Alder buckthorn (Frangula alnus) Size: 6 metres at maturity NHS Forest tree bundles: n/a | Thornless with smooth dark brown bark and narrow oval leaves, alder buckthorn is usually found on damp acidic soils and in boglands. Charcoal from this uncommon species was traditionally used to make gunpowder. |
 | Blackthorn (Prunus spinosa) Size: 6 – 7 metres at maturity NHS Forest tree bundles: Nature, Wild Food | A dense shrubby tree with toothed leaves and creamy-coloured flowers and blossoms in bloom from around March. The flowers develop into blue-black fruits called sloes which can be used to flavour gin. |
 | Crab apple (Malus sylvestris) Size: 7 – 9 metres at maturity NHS Forest tree bundles: Urban, Hedge, Wellbeing, Blossom, Wild Food | Britain’s native wild apple, this compact often gnarled tree has toothed oval leaves and sweetly scented blossoms. The fruit is often used to make jelly, or is an excellent source of food for wildlife, especially birds. |
 | Dogwood (Cornus sanguinea) Size: 10 metres at maturity NHS Forest tree bundles: Hedge, Nature | A small broadleaf shrub with oval leaves and creamy white flowers that bloom into spring before developing as small black ‘dogberries’. Dogwood is noted for autumn colour, its leaves turning crimson before they fall. |
 | Elder (Sambucus nigra) Size: 10 metres at maturity NHS Forest tree bundles: Wild Food | A mid-sized tree with grey-brown bark and feathery toothed leaves. Fragrant creamy flowers emerge from May and develop into small purple berries. Both flowers and berries are edible when cooked. |
 | Goat willow (Salix caprea) Size: 6 – 10 metres at maturity NHS Forest tree bundles: Shelterbelt, Nature | A small, scrub-forming tree with oval leaves and soft pawlike catkins, goat willow is commonly found in damp areas, woodlands and hedgerows. Salicin, the precursor to aspirin, is derived from (and named for) willow bark. |
 | Guelder rose (Viburnum opulus) Size: 4 metres at maturity NHS Forest tree bundles: n/a | Sprawling shrub at home on damp or chalky soils with broad three-lobed leaves and red berries. Common as an ornamental species, the presence of wild guelder rose can be an indicator of ancient woodland. |
 | Hazel (Corylus avellana) Size: 10 metres at maturity NHS Forest tree bundles: Grove, Urban, Hedge, Wellbeing, Blossom, Wild Food | Commonly coppiced for timber, hazel is a mid-sized tree with yellow catkins and small bud-like flowers; when pollinated it will develop oval fruits and ultimately edible hazelnuts enjoyed by humans and small mammals alike. |
 | Juniper (Juniperus communis) Size: 10 metres at maturity NHS Forest tree bundles: n/a | A long-lived conifer with small needle-like leaves, juniper trees can be used to create dense cover for wildlife. Berry-like purple-black female cones are commonly used for flavouring food and to relieve respiratory and digestive problems. |
 | Spindle (Euonymus europaeus) Size: + 6 metres at maturity NHS Forest tree bundles: Hedge | A small flowering tree with colourful autumnal leaves and vibrant pink and orange fruits. Although toxic to humans, spindle has historically been used for medicinal purposes and remains a haven for biodiversity. |
Did you know that NHS Forest has a tree bundle specifically for healthcare sites with limited space available for planting? The Urban mix is our smallest multi-species bundle with thirty smaller trees – 10 x crab apple, 10 x hazel and 10 x rowan. These trees will tolerate compact soils and thrive in built up areas, whether planted together in a group or dispersed. For more information or to request tree bundles for your site please visit our tree bundles page.
Ready to find out about care and maintenance? Read part 2 of this blog.