Once the overall process of sowing (germination, grafting) is over, the plants are transplanted into the block. This block gives the plants more volume to continue growing undisturbed. The start for this phase is given with initial wetting/saturation of the blocks with water and fertilisers. The method is explained for a wetting line, but the principle also applies if other systems such as a ‘wetting cart’ or ‘ebb flow in combination with the hose’ are used.
For the uniformity of the plant material, it is important that the blocks are all the same in terms of WC, EC and Ph, as the plants transplanted in the block should not lack anything. The start in the block must be flawless, especially for further rooting, which is why wetting the blocks is essential!
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Stone wool blocks are best saturated with water and fertilisers when the water is offered repeatedly. The fibres in the blocks will then become thoroughly wet, even over the entire height of the block. Starting from a freshening line, it is important to have 4 to 5 spray bars that bring the water to the blocks. The water must be given time to sink through the blocks, so a distance of 50 cm between the beams is optimal. If the distance is too short, a pool of water is created and there is no longer a flow of water from top to bottom along the fibres in the blocks. Air is thus trapped in the block, this stops complete saturation of blocks.
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It is ideal to use an ‘open’ belt under the spray bars. This allows excess water to drain well into the drain pan under the belt, reducing the chances of air trapping in the block.
The speed of the conveyor belt also plays a role here. Try to maintain a speed of 2-3 cm/sec. Too high a speed will cause the blocks to run under the spray bars too quickly, giving them too little time to properly absorb the moisture after each spray bar.
Furthermore, the water temperature should be above 18 degrees, optimum is around 21 degrees. If the water temperature is low, the fibres do not absorb the moisture as well.
If necessary, check the amount of water supplied using a ‘Grodan water volume bucket’. The rule of thumb is that this should be between 1.8 and 2.5 times the volume of a block.
It is important to weigh the weight of the blocks structurally and randomly after initial wetting. This should then also be noted on the freshening list. If blocks weigh less than the lower limit, this is a signal that the blocks have not been thoroughly wet. It is important to take action on this right away. Is the water offered irregularly? Is the water pressure sufficient and constant? If the blocks have not been wet properly, this leads directly to growth retardation and heterogeneity, so it is important to check and ensure this process regularly.
The minimum weights required after initial wetting of the most common block types:
| Block Type (LxBxH) | Block Volume | Min. Weight after initial saturation (grams) | ||||
| 100*100*65 | 650 CC | 553 | ||||
| 100*100*75 | 750 CC | 638 | ||||
| 100*100*85 | 850 CC | 723 | ||||
| 150*100*65 | 975 CC | 829 | ||||
| 150*100*75 | 1125 CC | 956 | ||||
| 150*100*85 | 1275 CC | 1084 | ||||
| 200*100*65 | 1300 CC | 1105 | ||||
| 200*100*75 | 1500 CC | 1275 | ||||
Key points:
Between different crops, different levels of EC are used during block wetting. The following guidelines are in place:
| Crop | EC standard | Generative | Vegetative | ||||
| Aubergine | 2,8 | 3,5 | 2,5 | ||||
| Cucumber | 2,2 | 2,7 | 1,7 | ||||
| Pepper | 2 | 2,5 | 1,5 | ||||
| Tomato | 2,8 | 4 | 2,5 | ||||
The pH used when wetting rockwool blocks should be between 5.5 and 6.
Grafted plants (tomato and aubergine) are always transplanted upright; this causes the rootstock to take root in the block and not the upper stem. The latter would undo the grafting and thus render it useless as a resistance to root diseases. Cucumbers are sown directly in the block, so transplanting is omitted there. With sweet peppers, most variations in transplanting techniques are:
Cucumbers are sown directly into the block, as this is a fast-delivery Crop, and the germination rate is usually very high, so low failure rate. By default, vermiculite is used after sowing to cover the seed. An alternative is the vermiculite-free block for cucumber. This block is designed to germinate without vermiculite. It prevents a lot of mess on floors and in watering systems. Ask your Grodan adviser for the possibilities.
After transplanting, the blocks are placed on the floor or table.
Place the slots of the block on ebb and flow floors in the direction of the drainage channel. This way, the water drains well after watering and the block is best protected against ‘wet feet’. As a result, the block can be optimally handled by a haul-out truck, which reduces the risk of breaking roots during expansion.
On tables, the position of the grooves only matters if the surface is completely flat. The groove should then face the drainage. However, the surface is often grooved and water will run off under the block via these grooves anyway. On tables, you do need to take the strongest side of the block into account with regard to expansion.
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