Preparing for a New Crop
With this 3-step approach, you will be ready for a new cultivation season on Grodan slabs.
1. Cleaning the Greenhouse
1.1 Before Cleaning
Grodan takes its position in respect to sustainable cultivation seriously. Before cleaning the greenhouse, please ensure that appropriate steps have been taken to minimise the emission of cleaning agents to the environment. For more information on emission and environmental policy where it applies locally, we advise that you contact your local Environmental Officer.
If the crop is infected with a disease, such as Verticillium, Bacterial Canker or an aggressive virus, seek specialist advice prior to cleaning. A robust hygiene protocol specific to your nursery is required in order to plan an affective clean up strategy.
Empty out the entire greenhouse: remove all plant material, slabs and floor polythene (if used). Sensitive equipment such as the WCM should be protected. Remove the sensor to the slabs. Due to risk of pest and disease, do not compost infected plant debris near the greenhouse.
If slabs are not placed in gutters, correct the soil profile if it is uneven. This will improve irrigation management and reduce risk of Pythium infection caused by pools of surface water. Be sure to create slight drain channels of 0.1% slope toward the end of the greenhouse.
If required, now is the best time to re-skin plastic greenhouses.
Before disinfecting the greenhouse, all surfaces need to be clean and free from organic matter. Check with your dealer for a disinfectant most suited to your needs. Treat the furthest bay from the door first and prevent re-contamination by clearly marking the cleaned areas.
Glasshouses need to be washed to remove dirt accumulated over the season in order to enable maximum light penetration for the new crop. Also, wash the greenhouse structure on the inside. With multi-year Mypex floor coverings, wash the floor with an appropriate disinfectant.
Work backwards towards the greenhouse entrance and prevent re-entry to cleaned areas. Use clean water applied with high pressure to wash. Detergent or acid can be added (for example, per-acetic acid, hydrofluoric acid or oxalic acid). For the outside, use an acid concentration of 10%; for the inside, use a concentration of 1%. As with all chemicals, use appropriate protective clothing when applying and read the manufacturer’s label before use. If you are in any doubt, please contact your dealer for the best course of action.
After 24 hours, wash again with clean water to prevent the glass becoming cloudy.
The irrigation system also needs to be cleaned: see ‘Cleaning and Checking the Irrigation system’.
1.3 Preparing for the New Crop
After cleaning and if required, new plastic floor covering can be laid. Multi-year Mypex floor coverings should be swept clean of plant debris and washed with an appropriate disinfectant. Make sure the polythene does not get contaminated: lay it onto dry soil and use two teams (one to remain on the bare soil and one on the plastic). Make sure that edges overlap sufficiently to prevent soil from uncovering later in the season, and also be aware of contamination of the concrete floor with soil debris by people walking back and forth.
Re-clean and sterilise the concrete floor once the polythene is laid. Lay out and space the new slabs. See ‘Handling and Placing of the Slabs’.
Do not forget before the new crop arrives to undertake some general housekeeping. For example, clean and disinfect grading and harvesting equipment, ensure drain water systems are clean, adjust the tension arms supporting hanging to enable free flow of drain water, and calibrate CO2 meters, temperature sensors and the light meter.
2. Cleaning and Checking the Irrigation System
Grodan takes its position in respect to sustainable cultivation seriously. Before cleaning the greenhouse, please ensure that appropriate steps have been taken to minimise the emission of cleaning agents to the environment. For more information on local emission and environmental policy, we advise that you contact your local Environmental Officer.
Use chlorine bleach (against organic organisms) and nitric acid (against inorganic pollutants).
Check if your drippers can stand a chlorine/acid treatment; if not, ask your dealer for the cleaning procedure.
Carefully read the labels of the chemicals prior to use.
Prevent contact between these substances, as there is a danger of lung burn and explosion.
Prevent the irrigation lines from becoming dry.
Clean the mixing tanks and the irrigation system.
The solution can be made in the mixing tanks: remove pH meters and put them in a pail of water. Also remove the EC electrodes.
If you have a drain system, fill up the drain basins with clear water so that the concentrated chlorine or acid will not affect the concrete.
Mix 4.5 litres of 10% concentration chlorine or 3.0 litres of 15% concentration chlorine in 100 litres of water. This solution has an EC above 10 and a pH between 10 and 11.
Add 3 to 5 litres nitric acid (38%) to 100 litres of water. A solution of 3% gives a pH of 1.5; and a solution of 7% gives a pH of 1.0 (depending on the quality of the water). The EC is between 7 and 9.
Flush the main and secondary pipes with clean water.
Apply the chlorine solution: it is ready when the last dripper has pH >10.
Leave the system filled for 24 hours, do not irrigate.
Flush the chlorine solution: rinse the pipes and mixing tanks with clean water, and irrigate for some time.
Add nitric acid and trickle shortly once per 3 hours to flush out chalk precipitation. Only run the irrigation system when the pipes are clean of any organic matter and the drippers are not dirty.
Flush the system thoroughly with clean water; no residues of cleaning product should remain.
Dip the irrigation pins into disinfectant solution for 5-10 minutes (when very dirty, for up to 30 minutes).
2.4 Checking the Level of Variation
When clean and before the new plants arrive, it is a good idea to check the uniformity of the distribution system.
Select 10 drippers from the first, middle and bottom irrigation line of a chosen irrigation section.
Place irrigation pins into empty bottles at various locations in the greenhouse.
Irrigate two or three times. Then use a measuring cylinder to record the volume of the solution in each bottle.
Add up the volume of these 30 drippers to provide a good insight into the output per section.
Download this file and enter the data on the 30 drippers to calculate the variation.
Calculation of the Result
5% variation is good – no action is required.
5% to 10% variation is poor – it is recommended that action be taken to correct this.
More than 10% variation is extremely poor – this will result in uneven slab water contents and poor water management capabilities if no action is taken.
3. Handling and Placement of the Slabs
3.1 Delivery on Pallets or Packs of Twelve
Outside storage is not recommended.
Store in a clean and dry area, separated from the production area.
Do not stack more than three pallets/slip sheets.
Make sure the pallets/packs cannot be accidentally damaged by vehicles or personnel.
Avoid contamination of the substrate or foil wrapping by keeping it away from dust, soil or exhaust fumes.
Leave the packaging intact until laying out the slabs in the greenhouse.
To ensure traceability make sure you retain any relevant delivery information, such as retrieval codes.
3.2 Laying Out the Slabs
Before laying the slabs, the greenhouse should be thoroughly cleaned: see ‘Cleaning the greenhouse’.
While unloading the pallets or unpacking the packs, handle the slabs carefully to prevent damaging the substrate or foil wrapping. Damage to the foil can result in uneven initial saturation, and it may lead to poor crop establishment and an uneven plant stand.
Make sure the slabs are positioned the right way up. Take note of the text and arrow on the foil wrapping. The ventilation hole and sealing strip are on the upper side of the slab.
3.3 Initial Saturation of the Slabs
If you have not ordered pre-cut plant holes, cut the planting positions in the foil wrapping based on the required plant.
Do not plant onto dry slabs.
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 initially be saturated the night before the young plants are delivered to the greenhouse.
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.
After filling, ensure that all slabs are correctly filled with nutrient solution. Top slabs 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.
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.
3.4 Cutting the Drainage Holes
Only do this when the slabs are fully saturated.
Grodan takes its position in respect to sustainable cultivation seriously. The best way to reduce emission of fertiliser to surface water is to recycle the drain solution from day one. 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 it 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.
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.
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 that more drain holes will make it harder to re-saturate 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. For more information, see the Grodan 6-Phase model.
The closest distance between first dripper and drain hole defines the water behaviour in the slab. The wider the distance, the more refreshment and re-saturation can take place in the slab. In the Next Generation assortment, the advice is at least 20 cm.
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 the block position at inter plantings on the same slab or the position of an extra dripper in the middle of the slab.
If the drainage system cannot process the large flow of drainage water when drain holes are made, start at the lowest point of the drain system (end of row) and work backwards towards the highest point (concrete path).
If circumstances – such as too high WC or a 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.
3.5 Planting the Crop
Agree with the propagator on the time of delivery and discuss the climate conditions during transportation so that the plants arrive in optimum condition.
Make sure the greenhouse and the slabs have the right temperature, for good rooting this should be between 18ºC and 28ºC. Allow two or three days of at least 19-20ºC to warm up the greenhouse. The maximum temperature difference between greenhouse and propagation is 3ºC.
When unloading the plants, avoid keeping them in cold areas such as the packing shed and move them directly to the greenhouse. Plant or place 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.
After planting, apply one or two irrigation rounds to even up the block WC and thereafter based on block WC 40-70% – climatic conditions permitting.