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Shade beneath a mature tree is one of the most demanding spots in any British garden. The canopy above intercepts the rain, the roots below take what is left, and the soil is often thin, dusty and threaded with hungry roots. None of that means you cannot have a lovely border — it simply means working with the tree rather than against it.

Before you buy a single plant, spend ten minutes assessing what you have. Is the shade light and dappled, as you would find under a birch or a rowan, or deep and constant, as beneath a dense beech, sycamore or horse chestnut? Does the tree lose its leaves in autumn, letting winter light and rain through, or is it evergreen and greedy all year? Which way does the border face? A north-facing strip under a mature oak is a very different proposition from an east-facing one that catches two hours of gentle morning sun.

It also helps to know your soil. Most established trees have drawn the nutrients down over decades, and where the canopy is thick, leaf litter may have made the top few centimetres slightly acidic. That suits woodland plants beautifully, so treat it as an opportunity rather than a problem.

Improving the Soil Without Hurting the Tree

The single most useful thing you can do is improve the soil — but gently. Forget double digging. Most of a mature tree's feeding roots sit in the top 20 to 30 centimetres, and slicing through them with a fork does far more harm than good, both to the tree and to the delicate fungal networks that keep it healthy.

Instead, mulch. Spread a layer of well-rotted leafmould, garden compost or a mix of both, about 5 to 8 centimetres deep, over the whole border. Worms will pull it down and improve the structure for you, holding moisture like a sponge through the driest weeks of July and August.

• Keep mulch clear of the trunk by 10 to 15 centimetres. Piling it against bark encourages rot and can attract pests.
• Never raise the soil level over the root plate. Even 5 centimetres of extra soil spread across the roots can smother them and cause dieback in the canopy above.
• Improve planting pockets, not the whole bed. If the ground is truly impoverished, enrich only the small areas where you are actually planting.

Planting Among Surface Roots

Planting under a tree calls for patience and a trowel rather than a spade. Choose a gap between the thickest roots and work the trowel in, easing smaller roots aside with your fingers rather than cutting them. If you meet a root you genuinely cannot avoid, and it is less than a couple of centimetres across, cut it cleanly with sharp secateurs instead of tearing at it. Anything thicker should be left well alone; find another spot.

Small is beautiful here. A 9-centimetre pot establishes far more readily than a two-litre one, because you are disturbing much less ground and can slot it into the space available. Autumn is the ideal time to plant, while the soil is warm and the tree is slowing down, giving roots months to settle before the dry season arrives. Firm the plant in, water it thoroughly, and keep an eye on it for the first two summers.

Plants That Earn Their Place in Dry Shade

Fortunately, some excellent plants evolved in exactly these conditions. Aim for a mixture of foliage, flowers and structure so the border carries interest from February to November.

• Ground cover: Geranium macrorrhizum, which shrugs off dry shade and gives you pink flowers in early summer; epimedium, with its delicate spring sprays; lamium; and tellima for its evergreen ruff of leaves.
• Structure and winter interest: hellebores, sarcococca with its sweetly scented winter flowers, skimmia, and the low-growing Euonymus fortunei for reliable evergreen colour.
• Ferns and grasses: Dryopteris, Polystichum and the tufted Deschampsia cespitosa all handle rooty ground with grace.
• Bulbs: snowdrops, cyclamen, winter aconites and daffodils, planted in autumn, flower before the canopy closes over and then quietly disappear.

Where the soil stays a little damper — perhaps on the northern edge of the canopy — brunnera, pulmonaria and astrantia will reward you handsomely.

Watering, Feeding and the Long View

Newly planted shade border plants need help for the first two seasons. Water deeply and occasionally rather than little and often, so the moisture reaches down to where the roots are. A slow trickle from a can, left to soak in, beats a quick sprinkle every time. Rainwater from a butt is ideal, particularly if your soil is on the limey side.

Feed sparingly. Heavy applications of nitrogen-rich fertiliser push soft, sappy growth that struggles in shade and can upset the tree's own balance. A light dressing of compost or leafmould each spring is plenty. Leave fallen leaves in place among the plants — they are free mulch and free food — but do clear them off small crowns and low-growing alpines, which can rot beneath a heavy, wet blanket.

Finally, resist the urge to tidy too hard. Seedheads, dead stems and old fern fronds shelter insects and frogs over winter, and a little natural litter is exactly what a woodland floor should look like. Get the soil right, plant small and plant often, and a shady border under a mature tree can become the calmest, most characterful corner of the garden.