Substrate composition and quality
Author: Ben Geijtenbeek – Senior Crop Technical Specialist – Syngenta Flowers
Ben Geijtenbeek has over forty years of experience as a technical expert in floriculture. He is specialized in educating growers in various cultures with new techniques and technologies. This way he revives the potential of Syngenta’s genetics, from the corporate philosophy “Bringing plant potential to life”.
Source and physical composition
The growing medium in which we grow plants can be made from several ingredients, like peat, coco fiber, coco peat, composted bark or other organic materials.
Growers base their choice on what’s available on the market in a consistent, reliable and affordable quality. These criteria exclude topsoil and clay, as they do not provide a consistent and reliable growing medium. The most important sources are peat and coco coir. Both have been proven suitable for decades.
A third option is composted bark, sometimes with additives like vermiculite. You can also mix these sources. But keep in mind that plants do not ‘eat substrate’. It is important that the quality is high enough to give the plant what it needs.
The substrate is a main quality driver and can be made in several ways and mixtures, as long it is controlled roughly according the following standards:
- Moisture 60 – 75 %
- Organic matter 80 – 90 %
- Bulk density 100 – 125 kg / m3
- Shrinkage (volume change) < 30 %
- Pores > 70 %
- Air porosity 16 – 25 %
- Easily available water 25 – 35 %
Besides this, we never want to have weeds, nematodes, fungi, pests and bacteria in the soil. This is the main reason why local topsoil is out of scope.
Do it yourself
- Buy or collect your organic material at least one year in advance.
- Put the organic material, for instance leaves or bark on a heap, and make it wet with water.
- The best is to add some Nitrogen (1-2 kg /m3) as Urea or Calcium nitrate to speed up the fermentation process, which is done by bacteria.
- Cover the heap with plastic to prevent drying out.
- After some time, the temperature inside the heap is going up.
- Temperature must reach around 60-70 degrees C. After a few weeks the temperature goes down.
- At that moment the pile has to be rebuild again, and the outside changed with the inside.
- By mixing it firmly, you give new oxygen and water to the bacteria. Add some more Nitrogen and let the process start again.
- A good composting process takes around 9 to 12 months.
- Due to the high temperature most diseases active in the organic material will be killed.
- Also unwanted organic oils from the bark will be decomposed, as well as insect eggs.
- The last step is to mix lime and other fertilizers to balance the EC and pH before potting plants in it.
Water and air capacity
Chemical characteristics as EC and pH
As you might know EC is the number that we use to describe the salt level of the substrate. The EC shouldn’t be not too high at the start of potting, around 0,6 – 0,8 EC. It can go up to 1,0 – 1,5 EC in the substrate later, depending on the crop and growth of the plant. These values follow the 1:1,5 analyzing method.
The second question that need to be answered is the composition of the EC. Does the soil contain just sodium and chlorine, or does it also contain valuable elements as Calcium, Magnesium, Potassium, and Sulfate? You can see these valuable elements as food for plants, that they need to grow. Keep them in line with the needs of your plant, balanced to promote a strong and healthy plant. This topic is of as important to maintain plant quality as the EC and substrate quality. In my next article I will share you more details regarding that subject.
With pH we express the acidity level of the substrate. A neutral pH is pH 7.0. But most plants need a slightly acid substrate with a pH of around pH 5.0-6.5. What happens with a wrong pH?