Start With Your Space, Not the Tree

Most disappointing garden trees are bought on impulse. A handsome specimen in a nursery pot, a sunny Saturday, and suddenly a plant that wants ten metres is sitting in a border that can only give it three. Before you open a catalogue, spend twenty minutes with a tape measure. Note the width of the border, the distance to the nearest wall or fence, and how close the boundary with next door actually runs. Then take a metre off each measurement to allow for maintenance access and future growth. What is left is your realistic planting footprint, and it shapes every decision that follows.

It also helps to ask what you want the tree to do. A single specimen for blossom and autumn colour is a different brief from a slim screen along a fence line, or a small tree underplanted with shade-loving perennials. Decide the job first and the shortlist becomes far shorter.

Mature Height and Spread Matter More Than Young Looks

Nursery labels are notoriously optimistic about size, so look for the ultimate height and spread rather than the height after ten years. In a small British garden, anything that will finish under eight metres is workable; under six metres is comfortable. Remember that spread is usually the figure that causes trouble, because it determines how much light your borders and windows lose.

• Very small (3–4m): Magnolia stellata, Acer palmatum cultivars, Corylus avellana 'Contorta' and most dwarf crab apples such as Malus 'Evereste'.
• Compact (4–6m): Amelanchier lamarckii, Sorbus aria 'Lutescens', Prunus 'Amanogawa' and Pyrus calleryana 'Chanticleer'.
• Moderate (6–8m): Acer campestre 'Elsrijk', Betula utilis var. jacquemontii and Crataegus monogyna.
• Avoid in small plots: Leyland cypress, Eucalyptus, poplar, willow and any large-leaved lime or oak. All are thirsty, fast-growing and difficult to keep in proportion.

Also check whether the tree is grafted onto a rootstock. For ornamental cherries and crab apples, a semi-dwarfing rootstock such as 'Colt' will hold the tree at roughly two-thirds of its normal size, which is often the difference between a tree that suits the space and one that swallows it.

Roots, Foundations and Boundaries

The old idea that roots mirror the canopy is a myth. Most fine feeding roots sit in the top 600mm of soil and spread well beyond the branch tips, which is why the tree's water demand matters more than its width.

On shrinkable clay soils, thirsty species can cause subsidence as they dry the ground beneath foundations. As a rule of thumb, plant trees that will exceed eight metres at least five metres from a house, and keep anything vigorous well clear of drains, patios and boundary walls. Where space is genuinely tight, a linear root barrier installed to at least 600mm depth, angled slightly away from the structure, gives useful protection. If you are planting near a building on clay, it is worth taking professional advice — the guidance in British Standard BS 5837 on trees and construction is the reference most arboriculturists work to.

Soil, Drainage and Aspect

Before buying, dig a spade-depth hole and squeeze a handful of soil. If it moulds into a smooth ribbon, you have clay; if it feels gritty and falls apart, it is sandy; chalk is pale, stony and alkaline; a dark, crumbly loam is the prize. Most garden trees cope with loam and clay, but chalk limits you to lime-tolerant species such as Sorbus, Crataegus and Acer campestre. Acid-loving trees like Amelanchier and most magnolias will sulk on chalk unless you plant them in a generous pocket of ericaceous compost.

To test drainage, fill the hole with water and see how long it takes to disappear. If it is still there after an hour, choose a damp-tolerant species or improve the ground with grit and organic matter before planting. Aspect matters too: a south-facing wall is warm and dry, while an east-facing border catches cold morning sun that can damage early blossom.

Light Levels and Shelter

Watch your proposed spot through a sunny day. Six hours or more of direct light suits flowering cherries, crab apples and maples. Three to four hours will still satisfy Amelanchier, hawthorn and most Sorbus. Deep shade under an existing canopy narrows the field to Acer campestre, Ilex aquifolium and shade-tolerant hollies and hornbeams.

Frost pockets at the bottom of a slope are worth avoiding for anything that flowers before May, as are exposed, windswept corners where young trees rock and roots struggle to establish. A little shelter from a fence or hedge makes an enormous difference in the first three years.

Planting and the First Two Years

Bare-root trees, planted between November and March, establish far better than pot-grown ones and cost considerably less. Dig a square planting pit roughly three times the width of the root ball but no deeper than the roots sit naturally — planting too deep is the single most common cause of failure. Backfill with the excavated soil, firm gently, and water thoroughly.

Stake only if the site is windy, using a short stake that allows the trunk to flex. Mulch 75mm deep over the rooting area, keeping it clear of the trunk, and water generously once a week through the first two dry summers. After that, most well-chosen garden trees need little more than a light formative prune and an annual glance at the ties.