Successfully underplanting trees: The best tips

Shallow-rooted trees in particular are not easy to underplant. With our tips, you can still bring the tree ring to life with underplanting.

Every property owner wants a garden that is green and blooming on several levels – on the ground as well as in the crowns of the trees. But not every hobby gardener manages to successfully plant under their trees and large shrubs: Most of the time it fails because of the right choice of plants, but sometimes it also simply fails because of the soil preparation and care.

Shallow-rooted trees such as spruce, Norway maple and birch are particularly difficult to plant under . They penetrate the topsoil intensively and literally dig up the water from other plants. Other plants also have a hard time in the root area of horse chestnut and beech – but here it is due to the unfavourable light conditions. Finally, the walnut has developed its own strategy to keep root competition at bay: its autumn leaves contain essential oils that inhibit the germination and growth of other plants.

Which trees are best for underplanting?

Apple trees , rowan trees , apple thorns (Crataegus ‘Carrierei’), oaks and pines are good for planting underneath . They are all deep-rooted or heart-rooted and usually only form a few main roots, which are only more branched at the ends. Suitable perennials, ornamental grasses, ferns and smaller woody plants therefore have a comparatively easy life on their tree disks.

Planting trees: the right time

Although you can plant trees under trees at any time from spring to autumn, the best time is late summer, from around the end of July. The reason for this is that the trees have almost finished growing and are no longer taking as much water from the soil. The perennials have enough time until the beginning of winter to grow in well and prepare themselves for the competition next spring.

How to plan a tree underplanting

The ideal plants – even for locations under difficult trees – are perennials that are native to the forest and are used to constant competition for water and light. Choose perennials according to their natural habitat for the location : for lighter, partially shaded tree disks, you should give preference to plants from the woodland edge habitat (GR). If the trees are shallow-rooted, you should preferably choose perennials for the dry woodland edge (GR1). Species that need more soil moisture (GR2) also grow under deep-rooted plants . For trees with a very broad, dense crown, perennials from the woodland habitat (G) are the better choice. The same applies here: G1 under shallow-rooted plants, G2 under deep and heart-rooted plants . When assessing the location, do not ignore the soil type. Sandy soils tend to be drier than loamy ones.

Ground cover for tree disks

The soil moisture in a tree ring also increases slightly from the inside to the outside: near the trunk, robust, drought-tolerant shade perennials such as Balkan cranesbill (Geranium macrorrhizum), golden strawberry (Waldsteina geoides), wood poppy (Meconopsis cambrica) or stinking hellebore (Helleborus foetidus) are in demand. The closer you get to the outer ring, the larger the selection of plants becomes: species that like it a little moister also grow here because the soil is better supplied with water when it rains. These include, for example, hosta (Hosta), heuchera (Heuchera), masterwort (Astrantia major), foxglove (Digitalis purpurea) and avens (Geum coccineum).

When choosing plants, make sure you choose a balanced combination of flowering and ornamental foliage perennials and also plan to include ornamental grasses and ferns in your planting. The Japanese ornamental fern, also known as the rainbow fern (Athyrium niponicum ‘Metallicum’), for example, brings a lot of color into play with its dark leaf stalks and light green to steel blue leaflets. The Japanese sedge (Carex morrowii ‘Variegata’) is an easy-care grass with creamy white leaf edges .

Don’t forget flower bulbs

Many bulbous and tuberous plants such as ray anemones, wood anemones , crocuses, winter aconites, bluebells and grape hyacinths are very well adapted to life under trees and should therefore not be missing from any tree planting. Many tulips and daffodils also feel at home here. Late summer is also a good time to integrate the bulbs and tubers into the tree ring when planting under the woody plants. As with perennials: arrange small bulbous flowers in large groups and taller species in small groups.

Once you have found the right plants, draw a scaled planting plan. To do this, transfer the area to be planted onto a white sheet of paper and draw the different perennials as symbols. Plant large species individually and arrange small ones in small or large groups. Large perennials and structural plants such as ferns and grasses should be arranged in the background.

Underplanting trees: A question of planting technique

When planting underplanting, ensure that conditions are good so that the perennials, ferns and grasses can gain a foothold in the dense root network. Remove the weeds thoroughly, but do not dig up the soil. Anyone who has tried it knows how difficult it is. It is not good for the trees either, because the roots are inevitably damaged. Also, do not add topsoil – many trees do not like this at all because their roots move into deeper layers of soil. And sooner or later suffer from a lack of oxygen. Copper beeches , horse chestnuts, walnuts and many rose plants such as apple trees. Cherry trees and plum trees are extremely sensitive to this.

After removing the weeds, first look for areas in the soil that have rather weak roots and mark them with thin wooden sticks. Then you should apply a three to five centimetre layer of humus. Either commercially available potting soil, bark humus or leaf compost. You can then lay out and plant the perennials according to your planting plan. Immediately before planting, you should immerse the root ball in a bucket of water until no more bubbles rise.

Finally, the entire area is watered thoroughly again and the tree disk is covered with bark mulch (chopped tree bark). The approximately five centimetre thick layer keeps the moisture in the soil and enriches. It with additional humus – an indispensable elixir of life for all forest perennials.

Care of a new tree underplanting

In the first two years, check the soil moisture regularly and water when necessary. Because during the budding and main growth phase (until the end of June). Shallow-rooted trees in particular extract a lot of water from the soil. In addition, dense treetops act like an umbrella and divert precipitation outwards.

It is also important that you keep weed growth under control: hoeinga is taboo when controlling weeds. As this damages the roots of the perennials and shrubs. Instead, you should pull out the unwanted plants by hand. After a few years, when the tree ring planting has closed, hardly any weeds will grow through anyway.

In spring, you should also spread three liters of mature compost per square meter, mixed with about a handful of horn shavings , on the tree ring to provide the perennials with nutrients. Once the area is dense, no further fertilizer is necessary – from this point on, the tree ring planting can largely do without care anyway.

Home and Garden