Mycorrhiza for old trees: How to strengthen existing trees

Table of Contents

• What is mycorrhiza?
• Why do old trees suffer from stress more often today?
• When can a subsequent application of mycorrhiza be beneficial?
• How do you introduce mycorrhizae to old trees?
• Why soil moisture is important for mycorrhiza
• Worm compost, mycorrhiza and soil life
• Mulch protects the soil
• How quickly will results be visible?

Large, old trees often appear robust and resilient. However, persistent drought, heat, and compacted soils are increasingly taking their toll on them as well. What many don't know is that even in old trees, soil life can be actively promoted. Under suitable conditions, mycorrhizal fungi can be introduced into the root zone even after the trees have matured. Whether a successful symbiosis develops, however, depends on the tree species, location, soil conditions, and any existing fungal communities.

This article explains when mycorrhiza application can be beneficial and what role water, mulch, and worm compost play in healthy soil life.

Key facts at a glance

• Mycorrhiza can be used not only in young trees, but also in existing trees.
• The mushrooms support the absorption of water and nutrients.
  
• Particularly weakened trees can benefit from promoting soil life.
  
• Drought stress, soil compaction and construction work can impair natural fungal networks.
• For successful colonization, the fungi need the closest possible contact with suitable fine roots.
• Sufficient moisture is crucial for the development of mycorrhiza.
• Mulch, worm compost and gentle soil care further enhance the effect.

What is mycorrhiza?

mycorrhiza This refers to the symbiosis between plant roots and certain soil fungi. The fine fungal threads connect with the roots and extend their reach in the soil. This often allows water and nutrients to be accessed more efficiently. In return, the tree supplies the fungi with sugars that it produces through photosynthesis.

This collaboration has existed for millions of years and is one of the most important natural processes in the soil. Most native tree species live in such a partnership with fungi.

Why do old trees suffer from stress more often today?

Many old trees have survived for decades without human intervention. However, their living conditions have changed in recent years. Among the most common stresses are:

• soil compaction
  
• Sealing of surfaces
  
• Construction sites in the root area
  
• Humus loss
• disturbed soil life
  

The combination of drought and compacted soils poses a particular challenge for many trees. Even large trees with deep roots can suffer from water scarcity as a result.

When can a subsequent application of mycorrhiza be beneficial?

Not every tree needs additional mycorrhizae. In natural gardens with plenty of humus, leaf litter, and active soil life, functioning fungal networks often already exist. However, supplementing them can be beneficial, for example, by:

• in visibly weakened trees
• soil compaction
• in humus-poor soils
• after construction work in the root area
• after prolonged periods of drought

Many older trees have lived in symbiosis with mycorrhizal fungi for decades. Therefore, additional inoculation is not automatically necessary in biologically active soil. It can be more beneficial in heavily disturbed sites, such as after soil alterations or when soil life is impaired.

How do you introduce mycorrhizae to old trees?

For mycorrhizal fungi to form a connection with the roots, they require the most direct contact possible with the fine root zone. Active fine roots are often located in the upper soil layers and can extend well beyond the drip line of the tree canopy. Therefore, mycorrhizal preparations are frequently applied directly into the soil of established trees.

Depending on the product and location, the preparation can be applied near the surface or directly into the soil where roots grow. Existing roots should be damaged as little as possible. For valuable old trees or heavily compacted soils, professional advice is recommended.

Why soil moisture is important for mycorrhiza

Mycorrhizal fungi are living organisms. They require moisture to become active and connect with roots. Therefore, the soil should not dry out completely, especially after application. Slow, deep watering can help create favorable conditions for the development of the fungal network.

Especially with larger trees, it is advisable not only to apply water directly to the trunk, but to consider the entire root area.

Worm compost, mycorrhiza and soil life

Mycorrhizal fungi are part of a complex soil ecosystem. Worm compost This system can support this in various ways:

• Promoting soil life
  
• Improvement of soil structure
  
• Humus buildup
  
• higher water storage
  
• Provision of organic nutrients

While mycorrhiza strengthens the fungal network, worm compost provides organic matter and promotes numerous other microorganisms. Many soil experts therefore consider the combination of fungi, soil life, and humus to be particularly valuable.

Mulch protects the soil

In addition, a mulch layer help to improve conditions for roots and soil organisms.

Mulch:

• reduces evaporation
• protects against overheating
• promotes the formation of humus
• supports soil organisms

Suitable examples include:

• Laub
• wood chips
• grass clippings
• bark

There should always be some space between the mulch and the trunk.

How quickly will results be visible?

It's impossible to predict whether and when an effect will become visible. Changes in root and soil life are often barely noticeable from the outside. Therefore, with older trees, the focus should be on long-term, favorable site conditions, rather than short-term growth effects. Success often becomes apparent when:

• through stronger sprouting
• through more vital leaves
• through better growth
• due to higher resistance to periods of drought