Our answers to your questions about our flax-based growing media

MWC weight (Maximum Water Capacity)

The Maximum Water Capacity is the amount of water that a growing medium can hold and the maximum weight that the it can take under the worst moisture conditions.

This index does not indicate whether the substrate structure is made of structural elements or not. The MWC weight simply indicates the weight of the substrate when waterlogged.

It is therefore a safety measure for a client or contractor to ensure that the proposed substrate meets - or does not meet - the weight constraints of the structure that will receive the growing media.

Therefore, the structure of the substrate cannot be determined from its MWC.

Roofing applications

For over  35 years, Terreau Flore Bleue has been supplying light soils and growing media substrates. The new range: URBAN VEGETALE® for extensive, semi-intensive and intensive garden roofs and terraces demonstrates our expertise, based on our know-how of the technical and quality control aspects of roof and terrace substrates.

There are many projects that have been delivered in the Paris region that adequately demonstrate this fact.

URBAN VEGETALE® standard NF U 44-551 is composed of mineral and organic materials, which form the backbone of the growing medium, around which the soil and flax will mass.

The raw materials used in the composition of the growing medium substrate have an almost identical density. Moreover, two of these materials (wood fibres and rock wool) have a stringy structure which results in a homogeneous product, allowing for the desired balance and stability of all the component materials.

The stringy part makes it possible to knit the component ingredients to one another  in order to keep the product consistent.

This prevents the organic matter from melting since it is distributed throughout in the mixture and its structural components..

Both the rock wool and the coarse wood fibres become a binder between the clay balls and the organic material. This prevents: 

• any losses of organic matter (OM), 
• the descent of this OM to the bottom of the growing medium during watering or heavy rainfall.

Consequently, the homogeneity of the mixture, composed of materials of similar density, allows the soil to be structured and ensures a consistent structure which will be compacted when laid and won't shift around afterwards. As a result, unlike a heavily mineralised product, water draining from the roof/terrace isn't blocked by the organic matter of the substrate.

When it is used on a roof, a coefficient of about 35% must be taken into account when calculating the necessary final volume of the site.

Finally, rock wool - coupled with wood fibre  - ensures natural water retention is possible. This allows plants to develop their root system towards the water source and also towards the source of the organic matter. 

Soil analysis

The analyses we provide are based on the reality of our materials and the mixture that are formed from them as well as drawing upon 40 years of experience with this same product range.

Analysis is carried out by approved laboratories recognised in the profession (AUREA, LCA, etc.).

The composition of a growing medium substrate

The use of wood fibre, allowed under the NF U 44-551 standard reference, is a growing medium support. We have worked to eliminate peat in 95% of our products in order to respect the environment..

This wood fibre, coupled with that of flax, brings a structural element and air porosity of the substrate due to its stringy and fibrous characteristics.

This property allows the different components to remain homogeneous and provides structure to the whole. In other words, removing it would be structurally unstable for the substrate. In addition, it is an excellent natural water retainer which does not rely on the use of chemical additives.

This alone is a strong environmental point, but you should also know that 60% of the substrate on offer from Terreau Flore Bleue is made of recycled products (rock wool, flax compost, softwood bark, wood fibre) specially selected for their origin, cleanliness and traceability.

As such, by using a Terreau Flore Bleue product, you are helping to preserve the environment.

Finally, our flax-based organic matter has a biological stability index of at least 95%.

Rock wool

Rock wool, derived by recycling from a clean activity, has fibrous, lightweight and water retention characteristics. These are neutral for the environment, plants and humans.

It is a material that remains homogeneous within the proposed growing medium substrate. Rock wool makes it possible to manage the watering aspect of the medium. Drying out will not affect the physical characteristics of this material. As such, it means that it can continue to retain water without any time limitation.

Therefore, automated watering can be left to the discretion of the professional, taking into account the growing medium of the roof/terrace and the palette of plants that have been chosen.

For all intents and purposes, rock wool is also used for hydroponic cultivation.

Finally, Terreau Flore Bleue's proven track record with manufacturing process means that the consistency of the mixture will results in a uniform substrate colour: dark brown throughout.

Granulometric data

According to the NFU 44-551 standards for substrates and growing media, up to now this type of analysis has not been required and it is not foreseen that it will be. For this reason, we do not provide such data.

However, the structure and the homogeneity of the densities of the substrate products offered mean that the mixture will remain in place once it has been compacted with a consistent level of organic matter available to plants.

References sites

Although each site is different,  reference sites do exist and have the merit of being able to demonstrate the reality and their effectiveness of our products in terms of their installation, the composition of the growing media and their durability.