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Growers use rockwool to produce specialty crops

While Grodan rockwool may be more often associated with greenhouse tomatoes and cucumbers, controlled environment growers are quickly learning that this substrate is an ideal choice for specialty crop production.

Many growers producing controlled environment food crops are familiar with Grodan rockwool. The clean, disease-free, inert substrate is used worldwide to produce greenhouse tomatoes and cucumbers. What growers may not be aware of is that Grodan rockwool can be used to produce specialty crops like strawberries, microgreens and hemp.

Grodan is working with a greenhouse grower in Canada who is producing a ½ acre of strawberries in rockwool slabs.

“The grower is producing most of his strawberry crop in coco coir slabs,” said Phil Johnson, who is Grodan’s business support manager for North America. “He wanted to trial Grodan, which he uses for his tomato crops, to see if he could achieve a similar level of crop control. The Grodan slabs the grower is using are similar in size to the coir slabs, it was an easy trial to set up.

“For propagation the grower uses primarily peat plugs. We also did a trial with Grodan rockwool blocks that would normally be used to propagate tomatoes and cucumbers. The strawberry plants went through the propagation process without any problems. The plants went into the cooler for their cold treatment and then were planted into the Grodan slabs and grew as would normally be expected.”

Before planting the ½ acre of strawberries in rockwool, the grower put in a couple rows of Grodan slabs in among the rows of coir slabs.

“The growth and fruit yield results of the trial were successful, so the grower expanded his production in Grodan to ½ acre,” Johnson said. “This trial proved that strawberries can successfully be grown in rockwool. There has been some discussion about strawberry plants needing to be grown in an organic substrate in order to be exposed to the biological organisms associated with substrates like coir. The trials we did with this grower debunk the misconception and clearly show that strawberries can be grown in an inert medium like rockwool.”

In respect to crop production, Johnson said the timing of the strawberry crop in Grodan was very similar to results with coir.

“We didn’t want to make any changes to the production strategies,” he said. “We were primarily interested in how the strawberry plants grew in rockwool. Historically strawberries have been produced in coir or field soil. It’s not a crop where there have been many studies done with inert substrates. Because strawberries can be successfully produced in rockwool we will focus our research efforts on this crop and will conduct trials to optimize the growing strategy to achieve better quality fruit, higher yields and better flavor.”

Austin Smith, U.S. commercial account manager at Grodan, said controlled environment production of strawberries eliminates unpredictable outside weather conditions.

“There are a number of diseases associated with field strawberry production,” Smith said. “One of the major benefits of growing strawberries in rockwool is sanitation. There are a number of diseases associated with field-grown strawberries. Rockwool is a sterile and inert substrate so that helps in regards to controlling disease.”

Johnson said most of the Canadian growers he is working with to produce microgreens in rockwool are new producers.

“Microgreens are a niche market,” Johnson said. “These new microgreens growers tend to go directly into rockwool.”

Grodan developed the Cress Plate specifically for the production of microgreens. This thin sheet of rockwool was designed for quick growing crops that need minimal substrate.

“Even though the Cress Plate is a thin sheet of rockwool it has all of the properties as other Grodan products,” Smith said. “The Cress Plate fits in 1020 trays which is the size growers use the most. Grodan has the ability to cut rockwool to order depending on the needs of the grower. If a grower needs a different dimension, Grodan can cut rockwool to that size.

“Grodan is improving the rockwool used to manufacture all of its products including the Cress Plate. The rockwool is NG 2.0, which is essentially a different way of applying the wetting agent so that it is closer to the fiber so that it absorbs water more uniformly.”

While both greenhouse growers and vertical farm growers are producing microgreens, Johnson expects the market will eventually evolve to be more indoor growers.

“Greenhouse growers are looking more at lettuce and other large leafy greens,” he said. “Microgreens will increasingly be produced in indoor vertical farms systems. Microgreens are more sensitive to high light conditions. Indoor growers have more control over the environment.

“There is also the economics of the crops. The inputs for vertical farms are a lot higher and microgreens are a high value crop.”

Smith said the Cress Plate allows greenhouse and vertical farm growers to start simple with 1020 trays.

“The Cress Plate is well positioned in vertical farm systems,” he said. “If growers are selling living plants the Cress Plate is well positioned to be able to be transported and moved around in the production system whether it’s in a greenhouse or vertical farm.

“Cress Plates are easily cut into smaller sections and can then be placed in clamshells for wholesale and retail sales. Many restaurant customers usually want the entire 1020 tray which makes them easier to handle.”

Doug Jacobs, technical advisor at Grodan, has been working with hemp growers in Canada and the United States.

“Grodan is a clean substrate that’s ideally consistent across the batch,” said Jacobs. “Grodan is available in standard plug sizes, 1-inch and 1½-inch. Either of those sizes would work for hemp propagation. Right now more growers are using the 1½-inch block or plug. I expect the 1-inch plug will be used more for tissue culture.”

Jacobs said most of the growers he has visited who are producing in warehouses are using some type of horticultural lighting.

“There is gradual change to LEDs from high pressure sodium (HPS) lamps,” he said. “LEDs have reached a stage of development where more growers are looking at them and are starting to choose them instead of HPS.”

Jacobs said growers who are propagating hemp are using mother stock plants and seed propagation.

“There are growers who are propagating from seed and selling the transplants to other growers who finish the plants. Some of it is being done indoors under lights and some growers are producing the finished crop in greenhouses. In the eastern U.S. many growers are buying the transplants from other growers and then finishing the plants.

Jacobs said depending on the production system, Grodan offers the ability to automate the system to control the growth especially with precision irrigation.

“When Grodan plugs are transplanted directly into the field it’s a matter of understanding that certain irrigation practices still apply,” he said.

“Once the plugs are planted into field soil the moisture is wicked out of the rockwool. In order for growers to be successful with transplanting rockwool directly into the field they need to incorporate some type of irrigation system for the transplants to root into the soil.”
Johnson said where hemp transplants are finished will impact how they are propagated.

“It depends more on where the plants are going to be transplanted, in a greenhouse or indoor grow or are they going out into the field,” he said.

“In a lot of cases it boils down to what is the production system. In the field the plants are going directly into the soil. Propagating the transplants for field production could be done the same way as transplanting for indoor grows.

“It’s about building speed into the plants. In any situation where a grower is trying to build speed into the plant, the substrate has to be matched to the size of the plants. If a grower has a seedling or vegetative cutting, the plants can go into a large plug, but it is going to take more time for the plants to produce enough roots to fill the plug. Depending on water content that could slow the plants down. Depending on the size of the plants a grower wants to have before putting them into a greenhouse, indoor grow or out into the field will determine the strategy for propagation. Whether there is too much or too little water in the plug, what a grower is trying to do is develop stem growth and leaf growth to sustain the transplants which is critical to ensuring good plant development.”

For more information:
Hort Americas

T +31 47 53 53 020
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