Gardening beneath an established tree is quite different from making an ordinary shaded border. Lack of light is only part of the difficulty. The tree already occupies the site above and below ground, intercepting some rainfall with its canopy while a much larger root system competes for the water, nutrients and soil space available underneath.

The most successful approach is therefore not to dig out the roots and remake the soil, but to work around the tree that is already there. Find the places where planting is realistically possible, use plants suited to the degree of shade and dryness, and give new roots enough moisture to establish before expecting them to compete successfully. Where the combination of shade and low moisture extends beyond the tree itself, our broader guide to dry shade gardening in Ireland explains the wider problem in more detail.

Start by reading the tree as well as the shade

Two trees casting what looks like similar shade can create quite different growing conditions underneath. A high, open canopy may allow broken light to move across the ground for much of the day, while a dense evergreen can exclude direct light almost continuously. Root systems vary too. Some trees fill the upper soil with a mass of fine competing roots, while others leave more usable pockets between larger roots.

Look at the whole area before deciding where to plant. Notice where rain reaches the soil, where exposed roots occur, how easily a hand trowel enters the ground and whether the soil remains moist a few centimetres below the surface after ordinary rainfall. Do not assume that the spread of the branches marks the end of the root system. Tree roots can extend well beyond the visible canopy, particularly towards areas where soil and moisture conditions are favourable.

The ground close to the trunk is often the least promising. Shade is usually stronger there, rainfall penetration may be poor and the structural roots are larger. Conditions often become more useful towards the outer part of the canopy, where more side light reaches the ground and there may be greater scope for finding spaces between roots. This is a useful tendency rather than a rule, so inspect the soil rather than choosing a planting line by eye alone.

Deciduous trees offer a valuable season of extra light

The conditions beneath a deciduous tree change markedly through the year. In late winter and early spring the branches are bare, so considerably more light can reach the ground. Once the canopy develops, the same position becomes cooler and darker just as the tree itself begins drawing more strongly on the available moisture.

Plants that make early growth can exploit this temporary advantage. Small bulbs are particularly useful because they require only modest planting holes and can flower before summer shade becomes dense. Cyclamen coum, for example, can occupy small, well-drained pockets beneath suitable deciduous trees and provides low winter and early-spring flowers when the canopy above is still open.

Early-season plants do not remove the need to judge summer conditions. A position that is bright in March may be deeply shaded in July, so anything remaining in active growth through summer must still tolerate the later reduction in light and, where roots are competitive, a much tighter supply of moisture.

Find planting pockets instead of cutting through roots

The tree should be treated as the dominant plant in the bed. Digging a large conventional planting hole through established roots merely to fit a new perennial into a predetermined position is the wrong way round. Large roots are part of the tree's structural and physiological system, and significant damage is not justified for the sake of underplanting.

Instead, make a few small trial holes with a hand trowel. If one position contains a dense mass of substantial roots, move a little farther away and try again. Where larger roots diverge, the spaces between them can form useful planting pockets. These may be irregular and may not correspond perfectly with a planting plan drawn on paper, but adapting the design to them is preferable to forcing the roots to accommodate the design.

Avoid rotavating or deeply cultivating the whole area beneath a mature tree. Even where no large roots are visible at the surface, large numbers of finer absorbing roots may occupy the upper soil. Cultivate only the places that genuinely need to be opened for planting, and leave the rest of the root zone as undisturbed as practical.

If the proposed work would require cutting substantial roots, altering the ground level significantly or carrying out major work on the tree itself, the planting plan needs to change. Where the health or structural stability of a valuable tree is in question, advice from a suitably qualified arborist is more appropriate than experimentation with a spade.

Smaller plants are often easier to establish beneath mature trees

A large container specimen may look as though it will produce an instant result, but underneath a tree its large root ball demands a correspondingly large hole. A younger plant with a smaller root system can often be fitted between existing roots with much less disturbance and can gradually send new roots through the spaces that remain available.

This is particularly useful with spreading perennials. Epimedium × versicolor 'Sulphureum' can be started in a workable pocket and allowed to build a wider colony as it establishes. Its fine underground growth has a better chance of finding its own route through the soil than a large root ball forced into a cramped hole beside structural tree roots.

Geranium macrorrhizum is useful for the same reason in suitable dry shade. It spreads by rhizomes and can gradually occupy ground around established woody planting rather than requiring every square metre to be dug and planted individually at the outset. In a natural-looking underplanting, that gradual movement is often more convincing than a rigid grid of mature specimens.

Improve the soil from the surface

Many woodland and shade plants respond well to soil containing decomposed organic matter, but the normal advice to dig generous quantities of compost deeply through a border is unsuitable where established tree roots fill the ground. The improvement has to be gentler.

Where a planting pocket can be opened without damaging important roots, loosen the soil only as much as necessary and incorporate a modest amount of suitable organic matter if the existing soil would benefit from it. Do not create a small container of exceptionally rich compost surrounded by hard, root-filled ground. New roots eventually have to leave the original planting hole, and a sharp difference between the pocket and the surrounding soil is not especially helpful.

Across the wider surface, leaf mould, well-rotted garden compost or another suitable organic mulch can improve conditions gradually without repeated cultivation. This resembles one of the useful processes of woodland soil, where organic material accumulates and decomposes from above rather than being dug through the tree roots every spring.

Adding a deep new layer of soil over an established root system is not a casual solution to a difficult bed. Roots need air as well as moisture, and raising the soil level substantially can alter the conditions around them. The base and root flare of the tree should remain visible rather than being buried beneath soil, compost or mulch.

Water new plants as though they are competing from the first day

A plant described as tolerant of dry shade may cope admirably once established, but that does not make a newly planted specimen drought-proof. At first its effective root system is largely confined to the original root ball, while the established tree is drawing water from a vastly greater volume of soil around it.

Water thoroughly after planting and continue checking the actual root zone during dry periods. A quick sprinkle can darken the surface without wetting the root ball beneath. Apply water slowly enough to soak into the soil, then allow conditions to guide the next watering rather than following a fixed daily schedule.

Rain elsewhere in the garden is not proof that plants beneath the canopy have been watered. Leaves and branches can intercept or redirect rainfall, and the soil immediately beneath a tree may remain much drier than an open border only a short distance away. Push a finger or trowel below the mulch and check.

Where a larger underplanting repeatedly dries, a seep or drip line can be useful because water is delivered close to the soil rather than sprayed over paths, trunks and foliage. It still needs checking. Root density and soil texture may cause one part of the bed to dry faster than another even when both are served by the same irrigation line.

Mulch after there is moisture in the ground

An organic mulch helps reduce evaporation from the soil surface and gradually contributes organic material as it breaks down. Beneath trees it has the additional advantage of improving the soil without continual digging, but it works best when there is moisture underneath it to conserve.

If the ground is dry, water first. A layer of roughly 5cm of leaf mould, composted material or another suitable organic mulch is ample for many underplanted areas. Keep it clear of herbaceous crowns and do not heap it against the tree trunk. A shallow, even woodland-like layer is useful; a mound built around the trunk is not.

Fallen leaves can form part of this surface layer where they are healthy and do not smother small plants. A light natural accumulation suits many woodland-style plants particularly well, although thick wet mats should be redistributed where they cover small evergreen crowns or emerging bulbs.

Plant from the easier edge towards the difficult centre

There is no virtue in beginning with the harshest piece of soil. The outer half of the canopy frequently provides a better starting point, with more light, a greater chance of direct rainfall and, in some trees, fewer large structural roots. Establish strong plants there first and allow those with a naturally spreading habit to extend into the more difficult spaces over time.

Pachysandra terminalis can make a useful evergreen carpet in deeper shade once established. It is a plant to use deliberately, however, because a happy colony can become dense and competitive with small, slow-growing neighbours. It suits a place where a continuous ground layer is actually wanted rather than a confined pocket between delicate specimens.

For a lower evergreen shrub layer, Sarcococca hookeriana var. humilis is useful in full or part shade and can form a spreading colony once settled. Give it a genuine planting pocket and enough room to develop rather than wedging a mature specimen between major roots. Its evergreen foliage also gives permanence to an under-tree area after many herbaceous plants have disappeared for winter.

Use ferns where both the species and the soil suit them

Ferns are closely associated with woodland planting, but they should not be treated as proof that every shady position is damp. Some require consistently moist soil and will struggle beneath a thirsty tree, while tougher species have much greater tolerance once their roots are established.

Dryopteris filix-mas, the male fern, is among the more robust choices for suitable dry shade. Its upright divided fronds also provide a useful contrast to the broader leaves of epimediums, hellebores and evergreen ground cover. Even a relatively resilient fern deserves careful watering after planting, particularly where tree roots quickly remove moisture from the upper soil.

Where the aim is specifically to develop a fern-led planting beneath trees, Laurel's guide to creating a woodland fern garden takes that specialist subject further.

Hellebores can use the brighter part of the under-tree season

Helleborus foetidus is particularly useful where a tough early-season perennial is needed in dryish shade. Its divided evergreen foliage provides texture through the colder months, followed by pale green flowers when much of the surrounding herbaceous planting is still dormant.

It is better placed in a reasonably bright pocket than forced into the darkest soil beside the trunk. Under deciduous trees it can take advantage of winter and early-spring light before the canopy becomes dense, while its established root system is capable of coping with leaner conditions than many moisture-loving woodland perennials.

Seven useful Laurel plants for planting beneath trees

No group of seven plants will suit every tree. A dense evergreen, a mature beech and a light-canopied ornamental tree produce different combinations of shade, dryness and root competition. These examples are useful because they perform different jobs within the underplanting rather than because they are interchangeable.

• Cyclamen coum: a small seasonal plant for well-drained pockets where winter and early-spring light reaches beneath a deciduous canopy.
• Epimedium × versicolor 'Sulphureum': a spreading perennial suited to shade that can gradually knit through gaps around established roots.
• Geranium macrorrhizum: a resilient rhizomatous ground cover, particularly valuable where the soil becomes dry once plants are established.
• Pachysandra terminalis: evergreen ground cover for darker positions where a dense spreading carpet is wanted.
• Dryopteris filix-mas: a robust fern for suitable dry shade, bringing upright finely divided foliage to the lower planting.
• Sarcococca hookeriana var. humilis: a low evergreen shrub for shade that can develop into a useful permanent colony beneath woody planting.
• Helleborus foetidus: an early-flowering perennial with distinctive evergreen foliage for suitable brighter dry-shade pockets.

For a wider choice, Laurel's ground cover plants and plants for full shade collections are useful browsing points. The collection label is only the beginning of the decision, however. Check each plant against the moisture, drainage, root competition and exact light available beneath your particular tree.

Some ground beneath a tree is better left unplanted

The urge to cover every piece of visible soil can cause more trouble than the bare ground itself. Immediately beside the trunk of a mature tree, where structural roots occupy the surface and little rain or light reaches the ground, intensive planting may demand continual irrigation and repeated disturbance for very little return.

Leaving this inner zone open can look deliberate rather than unfinished. A thin organic mulch, visible roots and trunks, or a path curving through the area can give the tree room to remain the principal feature. The stronger planting can then begin where conditions improve, forming a looser carpet around the perimeter instead of climbing unnaturally up to the trunk.

This restraint is particularly useful with an attractive mature specimen. The tree already provides scale, shade and structure; the plants underneath are there to complement it, not to conceal every sign of the root system that supports it.

Common mistakes when gardening under trees

• Assuming shade means damp soil. Established roots and intercepted rainfall can make under-tree soil exceptionally dry.
• Choosing the planting position before checking for roots. Let usable gaps in the root system influence where plants go.
• Cutting substantial roots to make a large planting hole. Move the plant or choose a smaller specimen instead.
• Rotavating the whole area. Fine absorbing roots occur through the upper soil even when they are not immediately visible.
• Planting everything close to the trunk. The inner root zone is often the darkest, driest and least forgiving part of the site.
• Using large specimens where small ones would establish more easily. Smaller root balls usually require less disturbance and can adapt gradually to the spaces available.
• Neglecting a plant because it is described as drought tolerant. Mature tolerance develops only after the new root system has established.
• Giving the surface a quick sprinkle. Water needs to reach the root ball rather than merely changing the colour of the mulch.
• Adding a deep layer of new soil over the roots. Major changes in soil level can alter the root environment and should not be used simply to create an ordinary border.
• Piling mulch against the trunk. Keep organic material in a shallow layer over the soil and leave the base of the tree clear.
• Trying to plant every gap. Some of the hardest inner areas are better incorporated into the design as open ground.

Frequently asked questions

Can I cut tree roots to make room for plants?

Avoid cutting substantial roots merely to create planting holes. Look for natural gaps between roots, move the proposed planting position or use a smaller plant that requires less space. If work around an important tree would involve major root removal, the implications for the tree are more important than the underplanting and should be assessed professionally.

Where is the easiest place to plant beneath a mature tree?

The outer part of the canopy is often easier than the ground immediately beside the trunk because light and rainfall may be better and large structural roots may be less concentrated. This is not guaranteed, since roots can extend far beyond the branches, so make small trial holes and check soil moisture before deciding.

Can I put extra topsoil over exposed tree roots?

A light surface application of suitable organic material can help a planted area, but burying an established root system beneath a deep layer of new soil is a different matter. Avoid substantial changes to the soil level and keep the trunk and root flare clear. Work with the existing ground rather than trying to turn it into a raised conventional border.

Do plants beneath trees need regular watering?

New plants often need closer attention because their roots occupy a very small volume of soil compared with the established tree. Water thoroughly during establishment when the root zone is drying. Once plants are settled, the need varies with species, soil, weather and the intensity of tree-root competition, so check the ground rather than watering automatically.

What are good plants for dry soil beneath deciduous trees?

Useful choices include spreading epimediums and hardy geraniums, robust ferns such as Dryopteris filix-mas, hellebores, small early bulbs and carefully chosen evergreen ground covers. The exact palette should narrow as the shade and root competition become more severe. For a much broader comparison, see the best plants for dry shade in Irish gardens.

Can I make a woodland garden beneath existing trees?

Yes, provided the existing root system leaves enough usable planting space and the plant choices suit the actual light and moisture available. Begin with the more favourable areas and build the lower planting gradually rather than attempting to fill the whole root zone immediately. If the intention is to turn the wider space into a layered garden rather than simply underplant one tree, our guide to creating a woodland garden in Ireland is the natural next step.

A mature tree is not an obstacle that needs to be overcome before gardening can begin. It is the dominant feature of the site, and the underplanting succeeds when that fact is accepted. Use the seasonal light, find the spaces the roots leave available, establish smaller plants carefully and allow spreading plants to occupy the ground gradually. Some parts may remain open, but the areas that are planted will be much more convincing because the plants are growing with the tree rather than in spite of it.