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How do I create drainage holes in the substrate mats?

Drainage holes
Written by Roel Bijl | Last update: 21-6-2021

Drainage holes are created in the new substrate mats at the start of the growing season in order to allow excess irrigation water to drain from the substrate. The number of drainage holes and the position of these holes have a major impact on the crop. This is because these are in part decisive for the water flow in the substrate, the re-saturation capacity and the displacement of old nutrient solutions. Hence, it is very important that you create the drainage holes correctly. Our specialist explains this in this article. 

Creating drainage holes

  • Create drainage holes in the substrate mats at least 24 hours before planting to allow any excess water to drain from the mat. Ensure that no “dead” water remains at the bottom of the substrate mat, as this will have a negative effect on the development of the roots of the crop.
  • The distance between the first dripper and the drainage hole is decisive for the water behaviour in the mat. As the distance increases, the refreshment and re-saturation rates in the substrate mats become higher.
  • Drainage holes are made by creating vertical cuts of at least 3 cm, running from the bottom of the mat upward. The best place for drainage holes is between the plants, at the lowest point of the mat towards the slope. Create one drainage hole for every 133 cm of mat length. If the mats are longer, you can opt for one or two drainage holes. This depends on the preference of the grower (when in doubt: it is easier to make additional drainage holes during the crop cycle than having to close up existing drainage holes!).
  • Use your fingers to widen the drainage holes, so that they cannot get blocked during the crop cycle.
  • A large amount of waste water is released when creating the drainage holes. You can reuse this for the new crop or discharge it via the sewer system. If the drainage system cannot process the large amount of waste water, start making the drainage holes at the lowest point (the wall) first, working your way up to the highest point (the concrete path), step by step. In addition, you can opt not to drain all substrate mats on the same day, but to divide this. This way, you can use the drainage water from the first sections to create the nutrient solution for the next sections.

Video: How to create drainage holes in substrate mats

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Consequences of creating drainage holes incorrectly

In order to further emphasise the need for making drainage holes correctly, we have set out the consequences of making incorrect drainage holes below:
  • The difference in water content in substrate mats with 'proper' drainage holes and with 'poor' drainage holes can amount to as much as 5 to 7%.
  • A misplaced drainage hole can cause the roots of the plant to grow into the drainage profile, as a result of which diseases can spread quickly.
  • Drainage holes that are too close to the dripper cause accelerated drainage and low EC refreshment rates. This in its turn causes an unbalanced supply of nutrients and a higher EC than planned, resulting in less rapid growth of the plants and a disturbance in fruit quality.

Questions about creating drainage holes

If you have questions about creating drainage holes, or if you would like to receive customised advice, please contact Roel Bijl, our product specialist, or ask your question by completing the form below. 

Roel bijlOver Roel Bijl

Roel Bijl is product specialist plant resilience and substrates at Royal Brinkman and has over 30 years of experience in horticulture. Through his years of experience in the greenhouse, Roel knows all the ins and outs of horticulture and especially in the area of resilient cultivation and substrates.

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