Glossary
Canonical definitions of the technical, regulatory, and certification terms you find on Arber product pages. “X is Y” pattern, specific numbers, explicit regulatory references — because clear answers are the most effective way to explain a complex industry.
Regulatory framework
Natural plant strengthener
A natural plant strengthener is an Italian regulatory category. It identifies products of plant or mineral origin that strengthen the plant. It is not a registered plant protection product.
Defined by Ministerial Decree 6793/2018, Annex 5. It does not require PMC authorization. It does not carry a plant protection registration number. Its action strengthens the plant’s natural defenses. It is not a registered curative treatment against a specific pathogen. Neem oil, horsetail extract, nettle, and propolis are the most common natural plant strengtheners.
Biocide
A biocide is a product designed to destroy, repel, or neutralize harmful organisms. It acts through chemical or biological action. It is authorized under EU Regulation 528/2012.
Biocides include household insecticides (mosquito, fly, and ant control), chemical repellents, and disinfection products. Each biocide has a specific authorization number and a mandatory safety data sheet. A biocide acts on the environment or on people. This is different from plant protection products (PMC), which act on plants.
Presidio medico-chirurgico (PMC)
The presidio medico-chirurgico is a historical Italian category for household insecticides and disinfectants. Products are registered under Legislative Decree 540/1992.
From 2013, new products follow EU Biocide Regulation 528/2012. Pre-existing PMC products are in transition. Registration numbers follow the format “Reg. Min. Salute n. XXXXX”. This category is distinct from plant protection (phytosanitary) products.
Plant protection product
A plant protection product is a registered product for protecting plants from pests and pathogens. It is authorized by the Ministry of Health with a specific registration number.
It includes fungicides, insecticides, and herbicides for agricultural or horticultural use. It is subject to disclosure requirements: registration number, active ingredient content, CLP hazard pictograms, and pre-harvest interval (PHI). It is distinct from a natural plant strengthener, which is NOT a plant protection product.
Substrates and raw materials
Blonde peat
Blonde peat is the surface layer of a peat bog. It is light in color. It has high water retention capacity and low decomposition (Von Post H1–H4).
It is the main component of professional substrates. Its porous fibrous structure balances water and air in the root zone. It comes from the Baltic countries (Lithuania, Latvia, Estonia) or Germany. Block-cut blonde peat is cut in blocks rather than milled. This preserves the fibrous structure.
Brown peat
Brown peat is an intermediate layer of a peat bog. It is dark brown in color. It has a medium decomposition grade (Von Post H5–H7).
It is more structurally stable than blonde peat over time. It is used in formulas where storage duration or the growing cycle is long. It comes from the Baltic countries.
Black peat
Black peat is a deep layer of a peat bog. It is strongly decomposed (Von Post H8–H10). Its color is near black.
It is added in small amounts to substrates to increase cation exchange capacity and nutrient retention. It is not used alone. It tends to compact and reduce aeration in the root zone.
Block-cut peat
Block-cut peat is peat extracted in compact blocks rather than mechanically milled into milled peat.
Block cutting preserves the fibrous structure of the original peat. This gives better aeration and drainage in finished substrates compared to milled peat. It is the quality choice for professional long-cycle production.
Milled peat
Milled peat is peat extracted by mechanical milling. It is produced in particles of variable granulometry (particle size).
It is less expensive than block-cut peat. It is the dominant peat type in global production. The milling process partially compromises the fibrous structure. It is suitable for short growing cycles and economy formulas.
Pumice
Pumice is a light, porous volcanic rock. It is used as a structural and drainage component in professional substrates.
Typical granulometry (particle size) ranges are 3–8 mm and 6–14 mm. It is inert and sterile. It provides excellent drainage and aeration. It comes from Italy (volcanic areas of Lazio and Campania) or Sweden. It is preferred over perlite for long cycles because it is more stable over time.
Perlite
Perlite is a thermally expanded volcanic glass. It forms light, white, highly porous granules.
Typical granulometry (particle size) is 2–6 mm. It improves aeration and drainage in substrates for propagation and short cycles. It is lighter than pumice but less stable over time. It tends to break down under mechanical compression when pallets are stored for a long time.
Vermiculite
Vermiculite is a thermally expanded lamellar mineral. It has high water and nutrient retention capacity.
Typical granulometry (particle size) ranges are 0–2 mm and 0–4 mm. It increases the cation exchange capacity of the substrate. It maintains moisture around young roots. It is a key component in propagation mixes and seed cover in plug trays. It comes from Europe (Belgium).
Wood fiber
Wood fiber is a renewable structural component obtained from heat-treated wood. It is a partial alternative to peat in peat-reduced formulas.
It improves aeration and drainage while maintaining good water retention. It is chemically stable and permitted in certified organic substrates. It is the main component in peat-reduced products and professional mulches.
Green compost
Green compost is an organic soil amendment. It is obtained from the controlled composting of mature plant residues.
It is added to substrates to provide stable organic matter, natural soil microbiology, and buffering capacity. Compost maturity is the key quality factor. Only fully mature compost enters professional substrates. Immature compost causes nitrogen drawdown by the microflora.
Technical specifications
Von Post index (H1–H10)
The Von Post index is a scale from H1 to H10. It measures the degree of peat decomposition at the time of extraction.
H1–H4 corresponds to blonde peat (low decomposition, fibrous). H5–H7 corresponds to brown peat (intermediate). H8–H10 corresponds to black peat (strongly decomposed). A low index means better physical structure and drainage. A high index means greater nutrient retention capacity.
pH
pH is the measure of acidity or alkalinity of a substrate. The scale runs from 0 to 14. A value of 7 is neutral.
Most ornamental and vegetable plants prefer a slightly acid pH range. Acid-loving plants (azaleas, blueberries, camellias, blue hydrangeas) require a lower, more acid pH range. Uncorrected blonde peat-based substrates have a natural pH in the strongly acid range.
EC (electrical conductivity)
EC is the electrical conductivity of the substrate. It is expressed in mS/m or mS/cm. It indicates the concentration of dissolved nutrient salts in the circulating solution.
Low values indicate substrates pre-fertilized for propagation and seeding. Medium values indicate substrates for potting-on with a nutritional starter. High values are typical of enriched substrates for long cycles with integrated fertilization.
Granulometry (particle size)
Granulometry is the size distribution of the particles that make up a substrate.
It is expressed in millimeters (e.g., “0–25 mm”). Fine granulometry (0–10 mm) retains more water. It is suitable for seeding and young seedlings. Coarse granulometry (10–40 mm) drains better. It supports long growing cycles on benches.
Structure (Fine / Medium / Coarse)
Structure is the qualitative classification of the granulometry (particle size) of a substrate. The scale runs from Fine to Coarse.
Fine: small particle size, high water retention, suitable for seeding and plugs. Medium: balanced, suitable for small to medium pots. Coarse: large particle size, high drainage, suitable for large containers and long cycles. Structure is the first selection criterion for a professional substrate.
Dry bulk density
Dry bulk density is the mass per unit volume of a dehydrated substrate. It is expressed in g/L.
Typical values for peat-based substrates are 150–300 g/L. Lower values indicate a more aerated, lighter substrate (more fiber, more perlite). Higher values indicate a denser substrate (more brown peat, compost, mineral amendments).
PG Mix
PG Mix is a range of balanced mineral fertilizers with fine granulometry (particle size), produced by Yara. It is commonly used as a nutritional starter in professional substrates.
It is available in NPK formulations including chelated microelements. It is added to the substrate at a calibrated dose to provide balanced nutrition during the first weeks after potting-on.
Controlled-release fertilizer
A controlled-release fertilizer is a resin-coated fertilizer. It releases nutrients gradually over a defined period of 3 to 24 months.
Common commercial brands include Osmocote, Multicote, and Agrocote. Release speed depends on substrate temperature. It is used in substrates for long cycles or large containers where frequent liquid fertilization is not practical.
Sustainability and certifications
Peat-free
Peat-free describes a substrate formulated without peat. Peat is replaced by alternative components such as coconut fiber, wood fiber, green compost, perlite, and bark.
It is a response to European restrictions on peat extraction (UK ban 2026, EU target 2030). Technical challenges include replicating the fibrous structure, buffering capacity, and natural pH of peat. Arber is developing peat-free formulas as part of its product roadmap.
Peat-reduced
Peat-reduced describes a substrate in which peat is partially replaced by renewable alternative components.
It is a balance between sustainability and technical performance. It is simpler to implement than full peat-free. The remaining peat fraction maintains structural performance. A typical composition combines wood fiber and peat.
RHP
RHP (Regeling Handelspotgronden) is the Dutch quality certification for substrates and raw materials for professional horticulture.
It verifies composition, granulometry (particle size), chemical parameters (pH, EC), microbiological purity, and raw material traceability. It is the reference standard for the professional European market. Certification numbers follow the format “RHP-2024-LT-XXXX”.
RAL Gütezeichen
RAL Gütezeichen is the German quality mark. It certifies growing substrates that meet strict technical and environmental standards.
It verifies controlled raw material origin, agronomic parameters, and absence of contaminants. It is the reference standard for German-speaking markets (Germany, Austria, Switzerland).
FiBL
FiBL (Forschungsinstitut für biologischen Landbau) is the Swiss research institute for organic farming. It publishes lists of inputs permitted in organic cultivation.
Listing of a substrate or input on the FiBL lists is the main signal of suitability for certified organic growing. This is especially relevant for the Swiss market and central European markets.
HORTICERT
HORTICERT is a supply chain certification scheme for growing substrates and raw materials. It focuses on traceability, quality, and environmental responsibility.
It verifies origin, regulated extraction, quality control, and environmental compliance across the entire substrate supply chain — from raw material to finished bag.