RETENTIS® in the Mirabell Gardens: our contribution to a sustainable renovation

The rose garden in Salzburg’s Mirabell Gardens is being completely renovated, and we at AgroBiogel are involved with our product RETENTIS®. As part of the renewal, around 2,400 new rose bushes and the new box hedge edgings are being treated with RETENTIS® to ensure a stable supply of water and nutrients in the first years.

After around three decades of use, the rose garden shows clear signs of wear. The soils are considered depleted, many rose bushes are over-aged and the soil is heavily overgrown with weeds. From September 2025, the existing plants will therefore be cleared and the soil in the beds removed completely. A special rose substrate will then be brought in to form the new basis for the planting.

The redesign with new rose varieties, some of them insect-friendly, fresh box hedge edgings, decorative gravel and various ornamental perennials is planned for late autumn 2025 and spring 2026. The aim is for the rose garden to shine in full bloom again in summer 2026 and to make it even more attractive for visitors.

The officials of the City of Salzburg emphasise the importance of this investment. The secured funding makes it possible to restore this gem in the Mirabell Gardens to new splendour while creating a successful example of cooperation between the municipal gardens department and the construction department.

Modern irrigation and RETENTIS® for the best start

Hot summers in particular show how important green spaces are in urban areas. With new plants, a modern irrigation system and a well-thought-out soil concept, the rose garden is being made fit for the future. The redesigned area is intended to be an easily accessible place that both visitors to the city and the people of Salzburg can enjoy for a long time.

One technical focus of the renovation is the installation of an artificial irrigation system. The irrigation pipes are laid at a depth of around 30 centimetres. This position protects the pipes and at the same time encourages the roses to root deeply. Water is not only available right at the surface, but where the roots are meant to develop in the long term.

This is exactly where RETENTIS® from AgroBiogel comes in. The product is worked into the root zone of the around 2,400 roses and the new box hedge edgings. RETENTIS® stores water and nutrients in the soil and releases them to the plants when needed. This stabilises the supply in the first, particularly sensitive years, even though the artificial irrigation lies deeper and the plants are encouraged to root deeply.

In this way, the critical initial phase after planting is reliably bridged. The roses and box can establish better, remain more resilient during dry periods and use the new irrigation much more efficiently. Combined with the fresh rose substrate, this creates ideal conditions for strong, healthy plants.

Historic structure and modern accessibility

Despite the extensive technical and horticultural renewal, the historic character of the rose garden is preserved. The structure along Mirabell Palace is largely retained in line with the requirements of monument protection. Paths and beds keep their arrangement and position, so that the characteristic impression of the garden is maintained.

AgroBiogel and RETENTIS® as partners in this flagship project

We at AgroBiogel are pleased to be part of this important project in the heart of Salzburg with RETENTIS®. The combination of a listed historic garden, climate-resilient planting, modern irrigation and innovative water storage technology shows how historic green spaces can be taken sustainably into the future.

We are particularly pleased that grünplan Landschaftsarchitekten deliberately integrated RETENTIS® into the planning and that we were able to attend the site meeting with all parties involved on Monday, 17 November 2025. The work is being carried out by Jakel Grünbau in close cooperation with the dedicated team of the Stadtgärten Salzburg.

In the rose garden of the Mirabell Gardens, RETENTIS® supports the new roses and box hedge edgings in their decisive establishment phase. This creates a long-lasting, resilient planting that will provide an impressive display of flowers in the coming years.

If you are interested in using RETENTIS® in your own garden or landscaping projects, feel free to get in touch with us.