Planting around a tree base: The best companion plants for trees

Under many trees, the ground often looks uninviting: the grass grows sparsely, the soil is dry, and bare patches appear in summer. Many garden owners and tree sponsors therefore ask themselves: Is it even possible to plant anything under a tree?

The answer is: Yes. With the right companion plants, a tree disc can not only look more beautiful, but also actively contribute to the health of the tree.
A planted tree base protects the soil from direct sunlight, reduces evaporation, promotes soil life, and helps retain moisture in the soil for longer. It thus performs similar functions to the natural ground vegetation in a forest.

This article will tell you which plants are suitable for planting under trees, what special features different tree species have, and how to plant a tree disc gently.

Key facts at a glance

• Trees often face difficult conditions due to shade, root competition, and dryness.
• A planted tree base protects the soil from drying out and overheating.
• Ground cover plants and shade-tolerant perennials are particularly suitable for underplanting.
  
• Shallow-rooted tree species are more difficult to underplant than deep-rooted ones.
  
• When planting, tree roots should be damaged as little as possible.
• Some companion plants can additionally enrich the soil with nitrogen and improve the soil structure.
  
• Mulch, compost and worm compost promote the development of living soil.
• During dry summers, the tree and its companion plants need sufficient water.

Why does so little often grow under trees?

Anyone who has ever tried to plant something under a large tree knows the challenge: many plants grow poorly or disappear again after a short time. There are several reasons for this:

The tree canopy intercepts some of the rain while simultaneously reducing sunlight. Furthermore, the tree roots compete with other plants for water and nutrients. Especially during dry summers, this creates a challenging environment for many garden plants.

Furthermore, some tree species spread their roots directly beneath the surface. This leaves very little soil available for other plants to root in.

Why a planted tree pit is often better than bare soil

Many people leave the area under the tree bare or try to grow grass there. From an ecological perspective, however, this is often not the best solution. A dense ground cover can help:

• to lower the soil temperature
• to reduce evaporation
• building up humus
• To promote earthworms and microorganisms
• to protect the soil from drying out
• to increase biodiversity in the garden

Nature shows us the way: In the forest, you rarely find bare soil under healthy trees. There, herbs, ferns, mosses, leaves, and dead plant material ensure permanently protected soil. Well-planned underplanting can fulfill this function in the garden as well.

Which trees are suitable for underplanting?

Not every tree species is equally suitable for underplanting. For example, fruit trees, oaks, pines, larches, and sweet chestnuts are relatively easy to plant.

Here, a large portion of the roots are located in deeper soil layers, so companion plants often find ample space. It becomes more difficult, however, under birch, beech, maple, spruce, and walnut trees. These trees frequently form a dense root network just below the surface. As a result, companion plants compete more intensely for water and nutrients.

Which plants are suitable for underplanting?

Here is an overview of various plants that are suitable as companion plants for trees:

Ground cover plants: Protect the soil permanently

These plants form a dense carpet, thus protecting the soil from heat and evaporation.

• Barrenwort (Epimedium): ideal for dry shade
• Cranesbill (Geranium): robust, easy to care for, good ground cover
• Barren strawberry (Waldsteinia): evergreen, drought-tolerant
• Evergreen (Vinca minor): green year-round
• Foamflower (Tiarella): a beautiful ground cover for partially shaded locations

Flowering plants and perennials: Promote biodiversity

These plants bring color to the tree disc and provide food for insects.

• Columbine: popular with wild bees
• Lady's mantle: easy to care for
• Violets: early flowers for insects
• Autumn anemone: late flowering
• Leopard's bane: blooms as early as spring
• Bergenia: robust leaves, early flowering

Near-natural forest plants

These plants also grow in forests.

• Woodruff: classic woodland ground cover
• Ferns: structurally rich and shade-tolerant
• Fragrant Hosta: large decorative leaves
• Lungwort (Pulmonaria): early flowering, important bee plant

For sunny tree discs

These plants cope well with drought and are also valuable insect plants.

• Lavender
• sage
• thyme
• Catnip
• oregano

Nitrogen fixers as natural soil helpers

Besides classic ground covers, there are several plants that can actively improve the soil. These include, for example, white clover, crimson clover, alfalfa, and lupins. These plants live in symbiosis with so-called rhizobia bacteria. The bacteria can fix nitrogen from the air and make some of it available to other plants in the soil. Therefore, such plants are often used as green manure. Under suitable conditions, they can contribute to:

• to promote humus formation
• to increase the biological activity of the soil
• to improve the soil structure
• to protect the soil from erosion

In orchards and natural gardens, such plants are often used as part of a living tree disc.

How to plant a tree disc correctly

When planting ground cover, you should proceed as gently as possible. It is important to note:

• Do not damage tree roots by digging.
• Dig only small planting holes
  
• Respect existing roots
• Do not use heavy machinery

The older a tree is, the more carefully you should work in the root area.
A thin layer of compost or humus-rich potting soil can make it easier for young plants to take root.

The water dilemma: Tree and companion plants share the same reserves

Even the best underplanting cannot completely compensate for drought. Trees and companion plants draw on the same water reserves in the soil. This can lead to additional stress, especially during hot summers.

Therefore, an adequate water supply remains important. Ideally, watering should be slow and thorough so that the water reaches both the tree roots and the surrounding plants.

A mulch layer or a dense plant cover also helps to retain moisture in the soil for longer.

Worm compost for a healthy tree base

Companion plants benefit from living soil. Worm compost It can help improve soil structure and promote soil life. It provides:

• organic nutrients
• humic acids
• microorganisms
• organic matter

This improves the soil's water retention capacity in the long term. At the same time, both the companion plants and the tree are supported. Worm compost can be particularly helpful in restoring the natural soil function to depleted or compacted soils.

Which plants should you avoid?

It's also important to note that not every plant is suitable for planting under a tree. Some species, for example, compete too strongly with the tree or make its maintenance more difficult. Therefore, you should avoid the following plants if possible:

• Vigorously growing plants can displace other companion plants and completely overgrow the root area.
  
• Large shrubs or trees often compete directly with the tree for water, nutrients, and root space. Therefore, low-growing plants are usually the better choice for tree pits.
• Water-hungry perennials further increase the water requirement. Especially in dry summers, this can intensify competition for already scarce water resources.
• Invasive plant species often spread uncontrollably and can displace native plants. Therefore, they should be avoided as much as possible in natural gardens.
• Plants with strong or aggressive roots compete particularly strongly with the fine roots of the tree and make it difficult for other companion plants to grow.

As a general rule, the less competition there is in the root zone, the better the tree and its companion plants can develop together in the long term. Low-growing, shade-tolerant ground covers and perennials that protect the soil without putting additional strain on the tree have therefore proven particularly effective.

Common mistakes when underplanting

Digging too deep

Damaged tree roots can impair the health of the tree.

Use plants that are too large

Larger shrubs often compete directly with the tree for water and nutrients.

Underestimating water requirements

Especially during dry summers, both the tree and the underplanting need sufficient water.

Leave the ground unprotected

Open soil areas dry out significantly faster and offer less habitat for soil organisms.