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Handling and placing of the slabs

Precautions before handling blocks and slabs in the greenhouse

Preparing for a new crop.

Before starting the preparation of your greenhouse for a new crop and you will install new Grodan products it is important to take the necessary pre cautions in order to work safely with our products. Grodan stone wool substrate is spun out of basalt and confectioned in to plugs, blocks and slabs. Stone wool may cause itching during use. Since most of our products are wrapped in a plastic foil, the risk to this will be minimal.

Eurima, the European Insulation Manufacturers Association, represents all major mineral wool producers throughout Europe. For its members, Eurima, developed a new set of recommendations, illustrated by new pictograms, for safe use of stone wool products and to prevent any skin irritation.

For Grodan products, these recommendations are especially important when installing new stone wool slabs in the greenhouse. Because Grodan products are wrapped in a plastic foil, precautions are minimal, however, when making use of bare stone wool products, like granulates, Grocubes or Grofit, good follow up of the instruction is recommended.

Please take a close look at the pictograms, you will find that most of them are just general so you can focus on the recommendations that apply for your working environment.

Cover exposed skin. When working in unventilated area, wear disposable face mask.

Cover exposed skin. When working in unventilated area, wear disposable face mask.

Rinse in cold water before washing.

Rinse in cold water before washing.

Clean area using vacuum Equipment.

Clean area using vacuum Equipment.

Clean area using vacuum Equipment.

Ventilate working area if possible.

Waste should be disposed of according to local regulations.

Waste should be disposed of according to local regulations.

Wear goggles when working overhead.

Wear goggles when working overhead.

Laying out the slabs

  1. Before laying the slabs, the greenhouse should be thoroughly cleaned. See 'Cleaning the greenhouse'.
  2. While unloading the pallets or unpacking the packs, handle the slabs carefully to prevent damaging the substrate or foil wrapping. Damage of the foil can result in uneven initial saturation and may lead to poor crop establishment and an uneven plant stand.
  3. Make sure the slabs are positioned the right way up: notice the text and arrow on the foil wrapping. The ventilation hole and sealing strip are on the upper side of the slab.

Initial saturation of the slabs

  1. If you have not ordered pre-cut plant holes, cut the planting positions in the foil wrapping based on the required plant.
  2. Do not plant onto dry slabs.
  3. Saturate the slabs at least 48 hours prior to the planting date to allow the solution to warm up and prevent transplant shock during planting. Proper saturation before planting is essential to establish and maintain the water characteristics of slabs. Under high light and temperature conditions temperatures in the root zone can become too high. High root zone temperatures (>26˚C) increase the risk of Pythium infection. To minimise the risk, the slabs should be initially saturated the night before the young plants are delivered to the greenhouse.
  4. Insert the irrigation pins into the stone wool but be careful not to push them through the slab. Gradually fill the slabs with the appropriate nutrient solution.
  5. After filling, ensure that all slabs are correctly filled with nutrient solution and top up manually if required. The foil wrapping should be bulging and the nutrient solution should be visible on the surface of the stone wool. Variations in water content at this stage will make accurate root zone management difficult and may create an uneven plant stand.
  6. Leave the slabs fully saturated for at least 24 hours to achieve the maximum capillary action capacity of the slab. An exception may only be made under extreme weather conditions when the slabs are saturated the night before to prevent the substrate solution from becoming too hot.

Cutting the drainage holes

Only do this when the slabs are fully saturated.

  1. Grodan takes its position in respect to sustainable cultivation seriously. The best way to reduce emission of fertilizer to surface water is to recycle the drain solution from day 1. When the drain holes are cut excess nutrient solution will flow into the drain channels. This solution will be clear, allowing UV systems to work effectively and will be perfectly balanced. Therefore provided the distribution system has been properly flushed with clean water it is perfectly safe to capture and re-use this solution on the new crop.
  2. The drainage holes can be cut 24 hours prior to planting. For optimum results it advised to place the knife underneath the slab and make the cut in an upward direction, (this will also avoid tearing the floor covering if hanging gutters are not used). The opening should measure 3 cm. To ensure the drain opening does not become blocked during the cultivation cycle widen the opening with your fingers. Never create a reservoir of ‘dead’ water at the bottom of the slab. This will limit root development and root function.
  3. One drain point is required per 133 cm slab. For slabs longer than 133 cm in length one or two drain holes can be cut, based on the preference of the grower. Please note more drain holes will make it harder to resaturate the water content in the slab in phase 3 and 4. Also more drain is needed to level the EC in the slabs. Especially in the steerable Next Generation assortment, the number and position of drain holes are important to focus on. More information on the Grodan 6-phase model.
  4. The closest distance between first dripper and drain hole defines the water behaviour in the slab. The wider the distance, the more refreshment and resaturation can take place in the slab. In the Next Generation assortment the advice is at least 20 cm.
  5. The cut should be made at the lowest point at the end of the slab in the direction of the slope. In case of an uneven profile, extra drainage holes will be required, once the slabs have settled at the lowest point. Never make the drainage holes directly underneath a propagation block or extra irrigation pin. Also be aware of block position at inter plantings on the same slab or the position of an extra dripper in the middle of the slab. 

Please note 
If the drainage system cannot process the large flow of drainage water when drain holes are made, start at the lowest point of drain system (end of row) and work backwards towards the highest point (concrete path). 

If circumstances (too high WC or more frequent watering strategy) are demanding for a change during the crop it is easier to make an extra drain hole than to reduce the number of drain holes in a slab.

Planting the crop

  1. Agree with the propagator on the time of delivery and discuss the climate conditions during transportation so that the plants arrive in optimum condition.
  2. Make sure the greenhouse and the slabs have the right temperature, for good rooting in this should be between 18 ºC and 28 ºC. Allow two or three days of at least 19-20 ºC to warm up the greenhouse. The maximum temperature difference between greenhouse and propagation is 3 ºC at the most.
  3. When unloading the plants, avoid citing them in cold areas such as the packing shed and move them directly to the greenhouse. Start planting or placing them beside the plant holes as soon as possible. Under extreme weather conditions plant in the early morning or wait until the evening when the temperature is lower.
  4. After planting apply 1 or 2 irrigation rounds to even up the block WC and thereafter based on block WC 40-70%, climatic conditions permitting.
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