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Picking a substrate mixture that offers the right amount of coarseness

April 6, 2022

The coarseness of a substrate mixture is one of its most relevant features. It influences the amount of support your plant roots receive, it affects the water retention of the substrate, and it also determines how well your plants can take up air, water, and nutrients.

If you suspect you aren’t using the best type of substrate for your crops you can always ask your Kekkilä Professional distributor for help in finding the right mixture for you.  

 Let’s have a look at some real-life examples that indicate the coarseness of the substrate mixture that’s being used does not fit your plant’s needs. 

Wrong coarseness causes lack of air 

Young Plants in substrate with wrong coarseness

This example shows an underdeveloped root system. As a result, these young plants will not be able to take up all the nutrients they need to grow into strong and healthy plants.  

 In this case, the issue is caused by using a substrate mixture that is too fine. That means there has been a lack of air for the roots to develop properly. 

 Instead, you’d like to see your seedling’s roots like this: well-developed, and evenly distributed throughout the plug with a lot of fine roots and root hairs.

Young plant growing in Kekkilä Professional substrate

Wrong coarseness causes lack of water and nutrients

Young plants growing in substrate with wrong coarseness

This example shows two young plants that have not been able to take up enough water and nutrients to meet their needs. Due to the coarseness not being right for this purpose, it didn’t provide good support for the root system. Consequently, when the plants were grafted the substrate couldn’t fulfill the demand of the graft for nutrients and water. 

 Instead, you’d like your young plants to look like this: 

Young plant growing in the right substrate

The correct coarseness of the mix provided good support for the root system to develop so when the tomato young plants were grafted they were able to take up enough nutrients and water. 

Wrong substrate coarseness causes a lack of support 

 This third and final example shows a mixture that is draining too much for this type of crop. In the picture on the left, you can see a young plant growing in a substrate mixture with unfit particle size. This particle size provides a bad connection between the roos and the substrate. As a result, the plant is unable to absorb the nutrients and water it needs to develop a strong root system and grow into a healthy plant. 

Young Plant growing in coir mix with wrong coarsenessYoung plant growing in Kekkilä Professional mixture


The young plant on the right is growing in a substrate of the right particle size. You can clearly see that the substrate is kept together by a good structure and strong root system, while the substrate on the left falls apart.  

To summarise, always make sure you use a substrate mixture that fits your growing methods and the needs of your crops.

In this training video our product manager Ned explains a little more about the way coarseness affects the air and water content within your substrate.

Watch other training videos on our video platform.


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