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How to choose the best substrate

Yes, how exactly? Listen to attractive offers of producers or suppliers? Follow the season’s trends? Buy what the neighbours buy? Follow the price? Many growers, even the really experienced ones, ask these questions at the beginning of every season, and not just in the Czech Republic. This annual dilemma is influenced by the economy and efficiency of growing different crops in our unregulated market environment where everyone can import and sell anything, no matter where it comes from. Let’s think about this for a moment and point out some of the overlooked, even intentionally sometimes, facts about this crucial decision-making process.

In any case, a correctly selected substrate is just one piece of the jigsaw puzzle that determines the grower’s success. The importance of substrate ranges between 10 – 25 % according to various authors. The rest are other components such as correct growing temperature, lighting, humidity (amount and frequency of watering), fertilization and plant feeding, prevention of pests and diseases, composition of air (carbon dioxide content), plant variety, growing technology (greenhouse, plastic tunnel, ...) and many other factors, which are sometimes hard to predict.


Many growers always consider price first, no matter what (but there are also exceptions, such as in Case Study 1). A general fact is that if a producer or retailer sells a substrate product at a noticeably lower price than similar products on the market, or sells all products for the same price, they usually know very well why they do so! Either they use lower quality materials or they might not have the latest equipment, their production capacity might not be sufficient, and they might not have an access to all sorts of facilities including their own laboratory. No grower can expect that such a product will match others that sell for much more. On the other hand, if you buy a very expensive substrate, it does not automatically mean you are buying the best product on the market!

Case Study 1
Grower A sows brassicas directly into cartridges with 160 cells. The consumption of substrate per one cartridge is approximately 4 litres. With a common price of the seeding substrate or special substrate for trays at 1.10 – 2.10 CZK per one litre it represents a direct material cost of 4.40 – 8.40 CZK per one cartridge. The value of the seed starts on 0.40 CZK per one seed. The cost of the entire cartridge is therefore 160 x 0.40 = 6 CZK!


Grower B uses the same cartridges and sows the same seed, but in a different substrate that costs 0.68 – 0.86 CZK per litre. He saves 1.68 – 4.96 CZK per 1 cartridge (35 - 59 % of the cost of substrate). But at the same time this substrate has a much lower germination performance due to high content of nutrients, which leads to salination. For every 10 % of the initial cost reduction it was actually necessary to spend 6.40 CZK more per the same amount of plants due to extra cost of seed. This grower is in fact knowingly losing 1.44 – 4.72 CZK per each sown cartridge just because of his choice of substrate (greater consumption of substrate, area and other extra costs are not considered)!


Commercially made substrates
Substrates made according to a recipe approved by a relevant state authority or upon grower’s specific requirements, on professional level and under strict laboratory supervision. The product fully meets the valid hygienic standards in terms of harmful substances. The substrate successfully passed testing in practical life and can be fully used without any reservations. Such a substrate cannot be blamed for a compromised growing result due to being improperly mixed.

Experiences from foreign countries, especially Germany, show that only 2 % of documented cases have been attributed to substrate failures. Unfortunately, 99 % of these cases it is bad choice to be blamed, both in terms of substrate composition or its purpose.

Commercially prepared substrates are gaining more and more advocates in the Czech Republic, who praise their availability and simple buying methods. There are several strong domestic companies with an annual production of tens of thousands cubic metres of substrates, as well as several local producers supplying smaller customers, and retailers of foreign products.


Own substrate recipe
In the past this was the key method of obtaining quality substrate and the pride of every proper gardener. However, own substrate mixing has lost its importance over time, especially due to its cost and ways of sourcing quality materials for mixing substrates.


Case Study 2

Grower C grows a culture of potted geraniums from purchased rooted cuttings. He uses special substrate that costs 850 – 1,500 CZK/m3 in the volume of 10 m3 per season.
Grower D grows the same culture, but mixes his own substrate from separate materials that he buys - 65 % peat, 20 % composted bark (in fact it sat in a heap for 2 – 5 years without any turning and was just sieved), 15 % clay (topsoil), fertilizer, limestone. The final price of all these materials is 700 CZK/m3. After mixing, he sends samples to an accredited laboratory for analysis that cost 750 CZK = 75 CZK /m3 when making 10 m3. Compare the achieved saving of 75 - 725 CZK per cubic metre with the value of the dead plants, although it is only 1 % higher. At the price of CZK 5 – 7 per one cutting this equals to 15 – 145 plants. Where is any saving?


A combined approach
Unfortunately some growers are still convinced that if they don’t improve a commercial substrate in their own way the success would be uncertain or there would be no success at all. In many cases they are just wasting time that they could use in a much better way, but most of all they are losing a lot of money on this kind of operations. By adding other components they are losing legal and practical claim in a potential complaint about a possible failure of a commercially produced substrate containing non-approved enhancements.


You cannot produce a quality, cheap and available substrate without quality and economically feasible raw materials. Professionals’ opinions divide between the fans of relatively cheap and accessible light substrates based purely on peat. Another group favours the more costly heavier types of substrates containing peat and bark and with good adsorption of nutrients and their slow release.



Many substrate producers are capable of defining their products in terms of pH and content of available nutrients. Not just by mere statement that their substrate contains a low, medium or high stock of such and such nutrient.

The trick of such statement is the fact that you can only compare what is comparable. This could be very hard even for the most respected experts. The pH value can be determined upon aqueous leach, from CaCl2 or even from KCl. The same applies to nutrients. In the Czech Republic we express their content in %, in volume or weight, in mg/100 g of dry or moist sample, in mg/l... The authorities are working hard on a declaration of  standard following EU norms.



This is often a critical point for the customers. Most of them want a loose product although they have absolutely no conditions for proper storage and they never buy as much as a really massive producer would. They also often incorrectly underestimate the fact that such a substrate must be efficiently transported to its destination, which may cost a way more than the actual product. If the storage conditions are poor, at least a part of the substrate is wasted – it can be contaminated by weeds, pests and diseases. Our foreign colleagues promote the opposite approach – most of their orders are much more varied, containing special substrates for different plant species in one shipment – because they know that packaged substrates are much easier to store and handle and they prefer 70 – 200 litre packaging, or 3,000 – 6,000 litre ones (big bags).



It would be completely wrong to think that it does not matter how, where, with what kind of irrigation, ventilation, etc. are the individual cultures grown. It is crucial to really adhere to suppliers’ or producers’ recommendations or to venture into the unknown of your own experiments with all positive and negative outcomes.

There is a golden rule that every system, if it is a system, must strictly follow its own rules. This also applies to the types of substrates we use.



In the imaginary value chart for choosing the best substrate this indicator should be the only one in the first place, no matter what! To save money on purportedly expensive substrates many growers buy a cheaper one with completely inadequate qualities in terms of physical composition, often with high content of dust particles. The fact that plants need a lot of air in their rooting zone is often overlooked. If the substrate contains too many dust particles, air is pushed away and the substrate becomes muddy after watering. Plants cannot develop their roots properly, they stop growing and eventually they die. Nowadays it is a trend to use coarser substrates than in the past when a single type was used from the sowing through potting to the final crop stage. The content of dust particles from milled types of peat (the most frequently used extraction method) must be strictly eliminated from further processing, which is just the case of block peat (it retains its original structure). Such substrates do have some negative traits and you must pay extra attention to watering and ensure frequent fertilization.


Responsible growers pay attention to these issues well in advance and not shortly before the first use of the substrate. It is also reasonable to exchange knowledge and experiences with respected colleagues, producers’ professional consultants or research professionals. To get the best choice options for an ideal substrate you also need to get a fair amount of reliable and accurate information regarding your crop, growing method, container size, irrigation, heating, ventilation, and many other aspects.

You need to select the best substrate also when you apply already produced plant material – e.g. when you plant pots and boxes, borders or trees, shrubs and lawns for your customers.


Ing. Jiří Valtera
Plant Growing Specialist

Centre Smiřice

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