This summer 2023 has been a dry harvesting season, which causes the product peat to go in the stockpile at a lower moisture content than usual. This can be beneficial for loading more volume per load as less water is transported. But the user of the peat or the substrate containing this peat should add water to the product supplied probably differently than usual. The WOK (Water Absorption Characteristic) of the product hasn’t changed, but the speed of the water uptake will be different and most likely slower than with a product at a higher moisture level. The WOK analysis developed by RHP provides insight into the water absorption rate of substrates. The WOK analysis examines the speed at which a substrate or peat absorbs water from an (air) dry situation. This provides insight into how a substrate absorbs water in a crop.

Growing Situations

With dry cultivation, ebb and flow cultivation and cultivation on an irrigation mat, the moisture content of the root balls can vary greatly. In these growing situations, quick and easy water absorption from the substrate is of great value. Limited watering or changes in the composition of the substrate mixture or the water regime can have major consequences for the water distribution in the pot (root ball), for example areas that are too dry.

Even Crop Development

The rate of water absorption can vary greatly per substrate. If a substrate can absorb water quickly from dry conditions, this can prevent problems with root balls drying out. Smooth water absorption helps to distribute the water and fertilizers evenly in the root ball. And that in turn contributes to good, even crop development.

Insight into Water Absorption Rate

Each part of a recipe has its own rate of water absorption. Insight into these values and how the raw materials and additives react to each other, is important to choose a substrate that best suits the cultivation situation and method of watering. The WOK analysis results provide insight and thus contribute to better crop management.

WOK Analysis

WOK (Water Absorption Characteristic) is a laboratory analysis in which a substrate is brought to a very low moisture content in a standard manner. The samples are then placed on a layer of water of a few milimetres for 24 hours. This examines how quickly the substrate absorbs water under dry conditions. The water absorption is measured continuously. The time in which the substrate reaches 50 percent of its potential water absorption is decisive for the water absorption characteristic.

WHAT TO DO IF THE PRODUCT IS DRYER

We advise to give smaller amounts of water and to increase the frequency of watering. If you have been supplied with peat and you need to mix it into a substrate, add water slowly, in the form of fine drops or in the form of shower or through sprinkler nozzles during the mixing process of the substrate; and if possible, for mixing when the peat is in bulk storage. This is a common way of adding moisture to a substrate. The dryer product is not different in comparison to a moister product in many ways, but to reach the level of a certain moisture content the road towards that is slightly different. A good start of the culture by moistening the peat step by step before potting, leads to a good result.

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Sometimes, at certain temperatures, water condensates between the peat bale and the plastic wrap, creating conditions conducive to fungal growth. If you notice white or yellow mould when you open the package of peat substrate, there is no reason to worry, it is Trichoderma or Peziza ostracoderma. It is a fungus of saprophytic origin (this means they only feed on decomposing organic matter), that is harmless to humans and plants. These are natural microorganisms that are found in almost all soils. Some of these microorganisms may even have beneficial effects on plant growth.

Sphagnum peat moss contains many microorganisms that occur naturally in peat bogs, such as the bacteria Bacillus, the actinobacteria Streptomyces, the fungi Trichoderma, Penicillium and Mucor. The presence of a healthy community of microorganisms in sphagnum peat moss makes it difficult for root rot organisms such as Fusarium to develop, because the inoffensive saprophytes compete with the pathogens for available resources. In addition, some species such as Trichoderma and Streptomyces synthesize molecules that are quite effective in suppressing some root rot pathogens.

Although there is no need to worry about plant safety, we can imagine that you want to limit the growth of fungi. Mould growth is only a visual problem. On top of the growing media fungi do not look nice and sometimes has a bad odor. The fungi usually have a white, yellow, beige, grey or brown colour. This colour is caused by the weft of the fungi that grows at the surface. The colour of the fungi may change during the life cycle.

White mould is Trichoderma – it is a naturally occurring beneficial microorganism that lives in most soils. Usually it’s presence cannot be seen, but sometimes it appears as white mould on the surface of the peat. Trichoderma is a group of saprophytic fungi that inhibit the growth of plant pathogenic fungi. Incidentally, it is also used as a commercial biofungicide because it prevents attacks by plant pathogenic microorganisms during cultivation. Thus, Trichoderma are particularly beneficial fungi that naturally protect the substrate from plant pathogens and do not have a negative effect on plants.

Yellow mould is Peziza Ostracoderma – commonly called cinnamon or peat mould. It is also a harmless but common saprophytic fungi found on peat. Saprophytic fungi live on other fungi in decaying organic material such as peat. They do not live on living plants.

The mould shown in the pictures mainly forms on the outer layer of the growing media, under the plastic bag or wrapping, where water tends to accumulate during long-term storage, which creates optimal conditions for the development of fungi. Mixtures with high amounts of fertilizers or those exposed to high temperatures during storage are more at risk of developing mold, but it can form on almost any peat-based products.

Recommendations

• Note that the peat is safe to use – plant growth will not be affected by these microorganisms.
• If you see fungi in the growing media, we recommend to loosen the compressed material and mix it thoroughly. This will disrupt the growth of fungi.
• It is not necessary to sterilize or use fungicides, because the mold itself is harmless and there is no fungicide specifically designed to destroy it. In addition, heating would kill the beneficial Trichoderma, and on the other hand, a sterile growing media would attract harmful fungi and promote their growth, as there would be no microorganisms such as Trichoderma to fight them.
• Once the growing media are taken into use for cultivation, the fungal growth will disappear and should not reappear in subsequent growth stages. However, it is important to note that if the growing media is kept too wet during the crop cycle, the populations of these microorganisms can increase significantly on the surface of the substrate in the pots. This can interfere with the distribution of water and penetration into the mixture. We recommend good irrigation practices, avoid overwatering the growing media and allow it to dry out to a certain extent before applying more water.
• Ventilate the greenhouse well.

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What Do the NPK and Numbers of Fertilizer Mean?

The three numbers represent the value of the three macronutrients used by the plant. These macronutrients are N (Nitrogen), P (Phosphorus) and K (Potassium) or NPK for short. These numbers indicate the percentage of nitrogen, phosphorus and potassium in the fertilizer. For example, a 14-16-18 mix means that the fertilizer contains 14% nitrogen, 16% phosphorus and 18% potassium. Plants require higher levels of nitrogen, phosphorus and potassium than any other plant nutrients. N, P and K are called primary macronutrients and are among the 17 nutrients essential for all plant life. Other elements, such as iron, are also just as important for plant survival, but plants need them in much smaller amounts. Also, different plants have different needs. In addition to the main nutrients, a quality fertilizer product will also contain small amounts of other nutrients, such as calcium, magnesium, iron. Below is an overview of the role of each major nutrient in the life cycle of a plant.

Role of Plant Nutrients

N (Nitrogen)

Of all the essential nutrients, Nitrogen (N) is required by plants in large quantities because it has important functions and can be a limiting factor in plant production and proper crop development. Nitrogen is necessary for the formation of chlorophyll, which is vital for photosynthesis – basically the way for plants to get food. Nitrogen is necessary for the development of the plant itself, it is a “building block” for amino acids, DNA, membrane proteins, enzymes, most coenzymes, auxins, cytokinins.

A high-nitrogen fertilizer is often used on grass, leafy vegetables or other plants where green foliage growth is more important than flowering. Without enough nitrogen, growth slows and lawns and plants turn pale. In contrast, when there is too much nitrogen, flowering and fruit-bearing plants struggle for green growth and lose their blooms and fruit.

Symptoms of Nitrogen deficiency

P (Phosphorus)

Phosphorus (P) plays a key role in the growth of roots, blooming, fruiting, seed formation, while also helping plants use other nutrients efficiently. Phosphorus increases disease resistance and is necessary for overall plant vigor and health.
As a result of phosphorus deficiency, plant roots become weak, flowers and fruits are missing.

The lack of phosphorus in plants affects the quality of the older and lower leaves. The leaves turn darker yellow or large brown, bronze or light blue spots appear. Leaves curl and thicken. Plant stems may turn bright purple or red. Usually the first sign is the darkening of the older leaves. Lack of phosphorus often leads to problems with pH balance or other nutrient deficiencies. Calcium deficiency is also possible in the plant due to the interaction between calcium and phosphorus.

K (Potassium)

Potassium (K) contributes to the overall health and vigor of the plant, strengthens the plant’s ability to resist diseases, helps the movement of water and nutrients in the plant, especially important in areas with a cold or dry weather (potassium helps to increase drought tolerance).

Potassium is often called a quality nutrient. Potassium affects the size, color and shape of the plant, as well as the taste of the fruit. Thanks to potassium, internal processes such as photosynthesis, energy supply, carbohydrate production and transportation are successful.

Symptoms of Potassium deficiency

• Mild chlorosis progressing into dry burns (brown edges, almost burnt-like)
• Veins become scorched or necrosis (dead plant tissue)
• Leaves tend to curl and crinkle

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European standard EN 12580

Determining the volume of raw materials and growing media is one of the most discussed issues in the substrate and potting soil industry. The packaged volume often causes some misunderstanding and confusion between supplier and customer. The indication of volume on BB bags is always the volume according to the European EN 12580 standard. Today, the European standard EN 12580 is applied by all professional manufacturers of peat products to ensure the same volume is packed. This is the volume of peat at the moment of filling the bags. Due to compaction, after packing the peat, the volume during use may vary – may be slightly lower.

The bulk density is determined according to the EN 12580 standard. Bulk Density times weight gives ENm³. The equation ‘ENm³-volume instead of m³-volume (water-volume). When following the ENm³ method – avoid discussion about volume and refute any accusations about incorrect calculations. For all Growing Media produced by SIA Zelta Zeme, the volume is measured in accordance with European Standard EN 12580. The standard specifies the procedure to be used for measuring the volume of peat products which are supplied in bulk or as packaged products. The quantity indication refers to the quantity at the time of production.

Peat products are delivered on a volume basis. It is very important that the measurement method EN 12580 is carried out completely correctly to ensure accuracy. The European standard EN 12580 describes in detail how to measure the bulk density of raw materials and potting soil. According to the method, sieves (fall controllers) with different mesh widths (20, 40 or 60mm) are used. An appropriate fall controller must be selected, depending on the product you want to measure. The purpose of the fall controller is to prevent the soil from falling from such a height that the material already in the cylinder would be compressed due to the impact of the falling soil. In addition, the fall controller also regulates the amount of material that can fall into the cylinder as a whole at a given time. Thanks to this method, the cylinder is filled homogeneously.

EN density = M3-M4/V

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Peat – Source of Humus

Peat is formed by incomplete decomposition and accumulation of bog plant residues, due to the lack of oxygen in waterlogged conditions. High bog peat consists mainly of various mosses. About 95% of the volume of peat moss is pores. The small pores are filled with water, and the coarse – with air, so the roots of the plants are provided with an ideal water and air balance. Peat is formed under anaerobic conditions and is sterile. It is acidic, with low  nutrients content, so adding liming material and composted with organic manure, peat is a high-quality material for the formation of humus in the soil.

Humus – the Basis of Soil Fertility

Humus is formed by  decomposed  organic matter. The content of organic matter increases the buffering capacity of the soil, making it more resistant to changes in pH. Increases microbiological activity in soil and promotes nitrification processes. Humus plays an important role in maintaining and improving soil fertility:

• promotes the formation of soil structure
• increases water infiltration
• improves aeration
• facilitates soil treatment
• reduces soil density
• creates favorable conditions for plant root growth.

Humic Acids

The most important component of peat for organic farming is organic matter. Peat is biochemically stable because it contains sparingly soluble humic acids. Humic acids are soil builders and growth stimulants that form calcium humate and calcium chelate complexes. The mineral part of peat is low in plant nutrients. Peat has antiseptic properties, they are determined by the acid reaction of peat.

Peat Use for Soil Improvement

The volume of pores in the soil and changes after the addition of peat are important. The pores vary in size. Wide pores allow water infiltration and aeration, but narrow pores allow to retain water. It is very important to maintain a balance between air and water for plant health and root development. Read More

Mixing peat to sand and clay soils significantly increases the number of pores containing water and air. The water and oxygen supply of plants is significantly improved. Improving the water supply also results in a more efficient supply of nutrients and faster plant growth.

Under natural conditions, the decomposition process of peat is very slow, but when mixed with soil, it accelerates. Bacteria play an important role in the biodegradation of peat. Bacteria use not only nitrogen but also carbon to synthesize proteins. Nitrogen is bound in bacterial cells for a while. Peat contains significant amounts of cellulose and hemicellulose, so it has a wide carbon to nitrogen ratio. Initially, after the addition of peat, microorganisms bind a lot of nitrogen, especially in the first two months, but later it is released.

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Growing Media Europe (GME) has issued the first sector-wide Growing Media Environmental Footprint guideline. Developed in strict accordance with the widely recognized European Union LCA standard “Product Environmental Footprint (PEF) Methodology,” the report combines the impact of 19 pre-defined environmental impact factors into one environmental footprint, enabling all producers of growing media to calculate the environmental impact of their product using the same calculation rules.

According to GME, one of the key findings of the report is that ‘peat environmental footprint scores are similar to those of non-peat components.’

If only carbon emissions are taken into account, peat scores higher than other materials, but referring to GME, the overall environmental impact of peat is lower than that of individual non-peat components. Also, the carbon footprint of peat is partially offset by the fact that peat is obtained only from previously degraded peat bogs. The harvested peat is transformed into valuable products used for food production, flower and tree growing, resulting in benefits for the environment and society.

“It is important to keep in mind that growing media are responsible for only a very small part of the total carbon and environmental footprint of growing plants. Because of this, the choice of growing media should be based not only on the impact of the growing medium itself, but also on its recyclability and the environmental footprint of the plant that is grown in it, ” says GME.

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It is estimated that the world’s population will reach 10 billion in 2050 and that 415% more substrates will be needed for food security, ornamentals and tree seedlings. The demand for horticultural peat will grow by at least 250% (taking into account the growth of other substrates by as much as 1000%). There is also talk of replacing peat substrates in horticulture with other substrates, but GHG emissions from the production and use of various peat substitutes are not always taken into account. Read more about the environmental impact of peat substitutes Is it Possible to Completely Replace Peat?

FACTS AND FIGURES

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Lately there is a lot of talk about the environmental impact of using peat in horticulture. As well as there is a lot of talk about sustainability, about products being green and environmentally friendly, but what do these terms really mean? The claim that the use of waste products such as coconut fiber or wood fiber is more environmentally friendly than the use of peat is in fact a debatable issue. It is not so simply as it might seem at first. The full life cycle of the material – production, processing, delivery, use and end of life – needs to be considered in more detail. Impacts on climate change, resources, human health and ecosystem quality need to be assessed. In fact, each raw material has an environmental impact. For example coir, compost, wood fiber, bark are subjected to one or more processing steps before they can be used as a component of growing media, resulting in environmental impacts.

We’re going to take a look at most important aspects must be taken into account when choosing the components of the growing media and the main disadvantages of most common peat alternatives, due to which these components do not meet the quality criteria.

Aspects to be taken into account when choosing a Growing Media

Changing the components of the growing media brings with it a great challenge in horticulture. Growers must adapt their cultivation practices -irrigation, nutrition application etc. in accordance with specific materials being used. Alternatives to peat that meet environmental requirements, as well as growers’ requirements in terms of certain characteristics, availability and price, are being actively sought and developed. Nothing has been found that works as well as peat for potting medium. Some products now offer mixtures of peat and other alternative components. The main reason for this is that however, alternative components cannot completely replace peat.

Main Disadvantages of the Most Common Peat Alternatives

Coir pith/dust

Wood – Based Materials

Increasing the use of wood-based materials in substrates, one of the many questions that growers and society often ask is about the sustainability of the use of wood (one of our most valuable natural resources). It should be borne in mind that some wood products are not by-products but are harvested from trees specifically intended for horticulture, so this is not positive from an environmental point of view.

Wood – based materials such as wood fiber, sawdust or composted bark products naturally contain nutrients. The manganese content is an important factor to consider when using these products in horticulture. Presence of wood based materials in growing media may strongly increase the manganese content.

It should be keep in mind that wood-based products bind a lot of nitrogen, because the material is decomposed by microorganisms. So, using such products requires more nitrogen fertilizer than peat.

Usually the material in different batches is inconsistent and you never know what chemicals the wood waste may contain.

Green compost

The composting process is the result of biological decomposition of organic materials, conducted by various microorganisms. The chemical and physical properties of compost can be quite variable, making it quite impossible to achieve product consistency from batch to batch. Another aspect that should be considered is the particle size. Compost is obtained by allowing organic matter to decompose. The small particle size of the final product creates a growing media with low air porosity and poor drainage, which means an unfavorable conditions for the plants.

Despite the fact that it is chipped and sorted before composting, it often happens that large pieces are found in the compost. This can cause problems using substrates such as sowing and plugging. In addition, pieces of plastic, stone, metal and glass can often be found in compost.

Nutrient imbalance can also be a problem when using green compost. As mentioned earlier, the nutrient levels in compost can vary significantly, no two batches are the same. Compost contains a lot of nutrients, but it is difficult to predict the release of these nutrients. In addition, if the composting processes are not completed before incorporation into the growing media, this may bind the nitrogen applied, resulting in a lack of nitrogen in the plants.

The microbiological activity of compost changes the level of nutrients in the growing medium over time. Nutrients are released as the compost is broken down, so over time and as the temperature rises, nutrients continue to accumulate in the unused growing media.

It is also important to know that high chloride content can be observed in compost, which may prevent plants from absorbing nitrogen.

In summer, it contains large amounts of grass that may contain herbicide residues that do not decompose and can harm plants.

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Wetting agents are a class of surfactants used to break surface tension and allow substrates to absorb water more easily. Wetting agents are especially important under dry conditions where the substrate  can develop hydrophobic properties – with tendency to repel water; unable to be easily wetted.

Hydrophobicity

Hydrophobicity is caused by various hydrophobic organic materials, such as organic acids, resins, wax. When they are dry, they form a non-polar coating on the substrate particles. Non-polar substances are not easily wettable in water, which is a polar substance. Then the coating repels water and the substrate in a dry state is unable to wet and to rewet.

How do Wetting Agents work?

Producing substrates, we add a wetting agent to ensure that the substrate will have good wettability. Wetting agents reduce the hydrophobic behavior of the substrate by decreasing the surface tension of the water. Due to its hydrophilic properties, it attracts water while adhering to a hydrophobic non-polar surface.

The purpose of using a wetting agent in substrates is to support re-wetting, especially during the first weeks of cultivation – its performance must be focused on this period. Once the root system in the pots has formed, re-wetting the substrate is easier, even if the wetting agent is no longer active.

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The physical properties of the substrate, such as porosity, pore composition and water holding capacity have a significant effect on plant growth and quality. By ensuring sufficient air, water and proper balance of available nutrients for plant roots, crop welfare is promoted. Stressed plants are more susceptible to diseases and pests, which increases maintenance costs and has a negative effect on profits.

Pore Space

The pore space is the volume available for air and water in a substrate. This means –  the volume of the substrate minus solids. Coarse particles in the growing medium create wide pores, which provide space for air exchange and  drainage. Fine particles create narrow pores that help  hold water.

The recommended range of air porosity for the growing medium varies depending on the crop and the stage of crop production. For germination or propagation medium, air porosity is recommended from 10-15%, while for most greenhouse plant growing media with coarse components, air porosity is recommended to be 15-25%, depending on the culture. Therefore, selecting the right growing medium for the crop type , it is very important for growers to maintain a balance between air and water in the substrate for plant health and root development.

Sphagnum peat has a very high porosity: pores filled with water and air make up more than 90% of its volume. Its structure is very stable over time to keep this porosity.

Pore Size

Substrate pores are of two types:

• Macropores are wide pores that allow water infiltration and aeration. Most of the water drains out from the macropores, thus lowering the water level of the substrate from saturation to water holding capacity.
• Mesopores or Micropores are narrow pores that allow the substrate to retain water. These types of pores retain water that is easily available for plants.

Water Holding Capacity

Water holding capacity (% ) is the percentage of total pore space that water occupies after excess water has been drained from the substrate. After draining the excess water, air fills the space the drained water once occupied. The substrate can hold water inside the narrow pores against gravity by capillary forces. Water drains out of the large pores because the force of gravity is greater than the capillary force in these pores.

The unique properties of sphagnum cells to retain and release water make peat products an indispensable component in soilless substrates.

The amount of water that the substrate is able to hold is the water holding capacity.

The water holding capacity of the substrate is not the same as the volume of water required to saturate the substrate. This is because at water holding capacity, both air and water space is at maximum in the substrate. Whereas at saturation all pores are filled only with water, this is not a good situation, because air is necessary for root growth. Total pore space affects the water holding capacity. Water holding capacity is considered to be a dynamic property of the substrate. It can be affected by substrate type, root growth and compaction.

The height of the container

The height of the container is one of the properties that affects the water holding capacity. Water holding capacity of the substrate decreases as the container gets taller. This is caused by the increased effect of gravity on the water column. Substrate’s water holding capacity increases with diameter of the container.

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ENSURE THE BEST AIR POROSITY FOR YOUR CROPS

The roots of the plant must needs the right balance of air and water. It is important that the substrate has the appropriate proportion of coarse and fine particles for the needs of the crop to be grown.

Coarse substrate particles create macropores that quickly release water, decrease water holding capacity and increase air porosity.

Fine substrate particles create micropores that increase water holding capacity and decrease air porosity.

Therefore, a substrate with a good ratio of coarse and fine particles may have a high water holding capacity, but it can be released evenly as root suction increases, creating appropriate air porosity as the substrate dries out between waterings.

Particle size affects the capillarity of the substrate, which indicates the distance water can be wicked by a substrate. The length of the capillaries in the coarse substrate is short and with a lower capacity to absorb water. In turn, the length of capillaries in small particles is long and able to easily wick water a longer distance within the substrate.

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The tray cells used for germination substrates are small, so finer substrates are used for this purpose, creating many micropores and limited air porosity. As the roots absorb the small water reserve inside the cell, it is replaced by air, thus ensuring the necessary air porosity.

SEEDLING SUBSTRATES BOOKLET

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Coarse substrates are used, for example, for container production. The coarse mixture provides a suitable ratio of air, water and solids. After saturation, most of the water will drain due to the large number of macropores, while part of the water will be retained by the micropores. Coarse fraction peat provides the same level of air exchange and drainage that can be achieved, for example, by the presence of perlite and vermiculite.

The Best Growing Media for Demanding Gardeners

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