Fertilizers and balanced nutrition for trees

1 Are Fertilizers Necessary?

Under ideal conditions, fertilizers are completely unnecessary in nature. This applies not only to trees but to plants in general.

Nature operates in a circular system and provides its own nutrients. The key elements that plants absorb from the soil are primarily nitrogen and minerals. These support the development of plant tissue, which is largely composed of carbon captured from the air through photosynthesis. These building blocks are found in organic matter and become available to plants as that material breaks down.

In our gardens, however, the situation is quite different.

Garden soil is often imported, compacted, or partially contaminated during the construction of the house.

In addition to disrupted structure, soil life is frequently disturbed, and construction residues such as cement may remain in the ground.

Natural processes are further hindered by the removal of fallen leaves.

No matter how many fertilizers are added, it’s not a sustainable solution without proper soil structure.

A healthy soil structure is created by living organisms that break down organic matter, supported by an optimal air-water balance.

A living soil therefore provides nutrients that are absorbable by plants.

Both soil life and the air-water balance can be supported by specific substrates and, in some cases, interventions such as drainage or structural adjustments.

2 When Should Fertilizers Be Added?

Soil life consists of living organisms—besides animals, mainly earthworms, insects, bacteria, and fungi.

Thanks to them, the elements needed for plant growth become more available and absorbable by the roots.

Adding nutrients to the soil makes sense under the following conditions:

When there is a deficiency or imbalance
When the nutrients are absorbable by the plant
When the soil structure and life support nutrient availability
The good news is that nature in our regions usually handles this process on its own. We can help support it, allowing for a quicker transition to healthy, living soil.

A healthy soil is not achieved by adding fertilizers, but by adding and supporting life and organic matter.

Soil organisms convert that organic matter into nutrients that plants can absorb.

In nearly all cases, organic fertilizer is the most suitable option.

Which Fertilizers Are Most Suitable?

Fertilizers contribute not only to plant growth but also to structural strength, leaf coloration, and overall resilience.

In nearly all cases, organic fertilizers are the most beneficial for the soil. This distinction is important: while the elemental nutrients for the plant are theoretically the same, the impact on soil health differs significantly.

Synthetic fertilizers are immediately available to the plant, but their dosage is more delicate and can easily lead to adverse effects, such as:

Depletion of soil life
Disruption of natural cycles and long-term soil health
Alteration of soil pH
Organic fertilizers require nitrogen to be mineralized by microorganisms before it becomes available to the plant. This natural process is more beneficial for the soil but takes time. Therefore, organic fertilizers are best applied in advance.

Key Advantages of Organic Fertilizers
No disruption to the ecosystem; stimulation of soil biology
Gradual nutrient release; reduced risk of leaching and overfertilization
Improved soil structure, enabling better root development and plant growth
 

Timing and Application of Fertilizers

Organic Fertilizers
Late winter: Application from late January ensures optimal nutrient availability in March and April.
Spring and summer: Unless maximum growth is required, fertilization during these seasons is not recommended. For newly planted trees (first year), fertilizing in spring or summer is strongly discouraged.
Autumn: A light application of low-nitrogen fertilizer can help trees enter winter in good condition.
Winter: Fertilization is generally ineffective, except at the very end of the season.
Synthetic Fertilizers
Rarely or never: These are best avoided. While there are specific cases where synthetic fertilizers may be considered, they fall outside the scope of this article.

Even organic fertilizers must be used with care. Prefer slow-release formulations applied in a timely manner so that nutrient availability coincides with peak uptake periods.

Otherwise, nutrients may leach into groundwater, where they are ineffective and environmentally undesirable.

 
Additional Considerations
High-quality espalier and parasol trees require less fertilization due to their slower metabolism. These trees grow more slowly, produce less leaf mass, and are more efficient in nutrient use.

For other trees and plants, fertilization needs depend on the type of garden:

In natural gardens where organic matter is retained, additional fertilization is rarely necessary.
In managed gardens where leaves and fine pruning waste are removed annually, and where the topsoil is inactive, an annual dose of organic fertilizer is beneficial. This is best applied between late January and mid-March.

What happens if you apply too much fertilizer?

First of all, it’s an unnecessary expense. Leaching fertilizers harm groundwater in the long term. Excess fertilizer can lead to unruly growth and increased maintenance. In some conditions, plants may become weaker. Finally, an overdose of fertilizer can cause root burn, resulting in plant death. Fertilizers applied right after planting are not always absorbed and may hinder the tree’s adaptation. (see: our advice)

Soil acidity:
Be aware that some fertilizers can affect the soil’s pH. This is especially important for acid-loving plants. Lime-based fertilizers or those with lime as a carrier should be avoided in such cases.

Fertilizing during drought:
Fertilizing in dry conditions requires a different approach. Water is key. Without moisture, fertilizer becomes a burden for your plants. Choose gentle, organic nutrition and give your soil the care it deserves. Sometimes, a mulch layer, soil improver, compost, bark or wood chips is a better option.

Conclusion and our advice:

Ensure good soil structure, starting with aeration.
Promote soil life: the richer the life, the healthier the soil.
Fertilize with slow-release organic fertilizers at the end of winter, so they become available in spring.
Too much fertilizer is pointless.
Fertilizers during the planting phase can reduce the tree’s resilience.
Fertilizing sandy soils:
Feeding sandy soil requires a specific approach, as it contains fewer nutrients and has a poorer soil life. The best solution is to use plants adapted to sandy conditions. In that case, only a yearly maintenance dose at the end of winter is needed. On sandy soils, it’s beneficial to add plenty of organic matter such as cow manure pellets, soil improver or compost.

In many cases, we advise against fertilizing immediately after planting. This encourages roots to search for nutrients and develop a stronger root system. A well-developed root system ensures better anchoring and helps the tree cope with stress periods like drought. What we recommend at planting is a good soil improver. Depending on your soil condition, we offer a standard version or a professional-grade improver. Always fertilize with organic fertilizers to support soil life and structure. Autumn fertilization requires a specific approach with tailored organic fertilizers.