Start With the Soil, Not the Sapling

Most tree planting failures I come across have nothing to do with the tree. A healthy two-year-old bare-root oak from a decent nursery is a forgiving thing. What undoes it, more often than not, is the ground it is asked to grow in. Soil does three jobs at once: it anchors roots, it holds water, and it holds nutrients. How well it manages each of those depends on the mix of particles beneath your feet — and that mix can vary enormously between one end of a garden and the other, let alone from one county to the next.

Before you spend money on trees, spend half an hour understanding your soil. It is the cheapest piece of gardening you will ever do, and it will save you far more than it costs in dead saplings and wasted weekends.

The Three Main Ingredients

Almost every British soil is a blend of three mineral particles, plus varying amounts of organic matter.

• Sand — large, gritty particles with big gaps between them. Water and nutrients drain straight through. Sandy soils warm up early in spring and are lovely to dig, but they dry out fast and leach nutrients quickly.
• Silt — finer, smoother particles, often laid down by rivers. Fertile and moisture-retentive, but prone to capping and compaction if you walk on it when wet.
• Clay — tiny flat particles that stick together. Clay holds water and nutrients beautifully, but drains slowly, swells and shrinks through the year, and is cold and heavy to work in winter.

Loam — the gardener's ideal — is roughly a balance of all three, held together in a crumb structure by organic matter. True loam is rarer than the gardening books imply.

Testing Your Soil at Home

You do not need a laboratory. Three simple tests will tell you most of what matters.

• The jar test. Half-fill a clean jar with soil, top it up with water, add a pinch of washing soda, shake hard and leave it for 24 to 48 hours. Sand settles first, then silt, then clay on top. The proportions give you your soil type; organic matter floats.
• The ribbon test. Take a walnut-sized lump of moist soil and squeeze it out between your thumb and forefinger. If it forms a ribbon longer than 5cm before breaking, you have a great deal of clay. Around 2–3cm is loam. If it simply crumbles, you are on sand.
• The drainage test. Dig a hole roughly 30cm deep and wide, fill it with water, let it drain, then fill it again and time it. Under ten minutes is fast-draining, several hours is slow, and still full the next morning is a genuine problem.

It is also worth knowing your pH. Most trees cope with a range, but some are fussy — beech and yew will take chalk, while birch, rowan and sweet chestnut prefer acid ground. Cheap kits are perfectly adequate. Failing that, look at what grows wild nearby: bracken, foxgloves and sorrel suggest acid; cowslips and salad burnet suggest lime.

Matching Trees to Ground

Once you know what you are standing on, choosing becomes much easier.

• Heavy clay. Oak, ash, hornbeam, field maple, wild cherry and crab apple cope well once established. Plant slightly proud, on a low mound of garden soil, so the root collar never sits in a puddle through winter.
• Light sand. Birch, rowan, Scots pine, hawthorn and sweet chestnut are in their element. Mulch generously and be prepared to water through the first two summers.
• Wet, waterlogged ground. Alder, willow, poplar and the damp-loving oaks will manage. If water stands for weeks on end, though, most trees will rot — consider drainage or a raised planting mound before planting anything.
• Chalk and limestone. Beech, ash, yew, field maple, whitebeam and wayfaring tree thrive here. Avoid acid-lovers such as birch and sweet chestnut, which will sulk and yellow.

Working With What You Have

Improving soil is a long game, and it pays to be patient. Spread well-rotted organic matter as a mulch over a wide area rather than digging a rich pocket into the planting hole: a compost-filled hole in clay simply becomes a sump, filling with water and drowning the roots. Keep mulch 5–8cm deep and clear of the trunk.

Do not over-enrich the planting site. A tree grown soft on rich ground puts on lush top growth at the expense of strong roots and often fails to anchor properly. If your soil has been cultivated intensively for years, it may also lack the mycorrhizal fungi that help roots gather water and nutrients — a handful of soil from beneath a healthy mature tree of the same species is a simple, free way to reintroduce them.

Plant Once, Plant Well

Plant bare-root trees between November and March, when they are dormant and the soil is workable but not frozen or waterlogged. Stake larger specimens for their first few years, and guard against rabbits and deer where necessary.

Above all, plant for the soil you actually have rather than the soil you wish you had. A birch on chalk will struggle for a decade and then die; a beech on the same ground will outlive you. Get the match right, and the tree will do the rest of the work itself.