Australian produce company Costa Group (ASX:CGC) has seen "phenomenal" results from the substrate production of blueberries in Corindi, and is now applying the method to farms in Far North Queensland, Western Australia and its overseas operation in China.

Costa Group horticulturalist Melissa Mullee

As part of the International Blueberry Organization (IBO) annual summit in Coffs Harbour, the ASX-listed company took participants on a tour of its farms in the area where it is producing 290 hectares of blueberries and 60 hectares of raspberries.

"One of the main reasons for us going to substrate is we've been growing on this land for 30 plus years, and the soils are pretty much exhausted," said Costa horticulturalist Melissa Mullee.

"We're going into fourth and fifth replants in our soils – to begin with we've got clay loams here and quite poor soil chemistry, and physical characteristics of low organic matter and low CEC (Cation exchange capacity)."

She said the process involves growing the plants in black 18-liter side-draining pots, sitting on top of pavers to make sure they're lifted from the ground.

"We're irrigating based on drain percentage and we're trying to achieve that highest drain percentage through the hot part of the day when the plants need more water and less fertilizer," she said, adding this was done using proportional injections with Netafim equipment.

"A benefit of substrate is the control of nutrition...some of the blocks are kilometers away from the irrigation shed, and we’re finding that in a substrate system every pot is essentially getting the same amount of water and the same amount of nutrition. That's why we're getting the uniformity in the plant growth.

"One of our challenges is we've grown quite quickly in substrate production. We started out with 450 pots and within the nine months after that trial we went to about 5,000 pots. We've definitely made mistakes but are learning from it – one of the important things is getting the irrigation right."

Mullee said substrate production can cost about five times more to set up than growing in soil, but the investment was worth it.

"The big cost associated with this is the tunnels and the irrigation, which is a capital cost so once you've got it in there's not really anything too much involved. It's just maintenance.

"In the soil we can irrigate every second day, every third day - we've got a bit of buffer in the soil - but in the substrate it needs to be watered every day and somebody needs to be monitoring it on a working day basis from morning to afternoon. It's a bit different but I think the yields are very rewarding.

"If we plant in September both substrate and soil, in the substrate we can get up to about 15 [metric] tons (MT) per hectare, and in the soil we'll be lucky if we get five [metric] tons."

She said the initial trial only lasted a few months until the team realized the phenomenal difference in growth.

"By the end of this year we will have 25 hectares in substrate. We are looking at converting our southern highbush plantings to substrate. It is a priority for us," she said.

"The practices we have learnt at Corindi are being applied to our farms in Far North Queensland and Western Australia as a starting point. We are also applying similar practices to our China operation."

In terms of other growing issues, Mullee said a plant called borridge was planted to attract bees which were sometimes hesitant to enter the tunnels. Netting is also essential to keep out birds, but with holes big enough so that pollinators can enter.

Borridge plants are used to attract bees which are sometimes hesitant to enter the tunnels.

"It's a big problem for the early varieties – we get some fruit that's quite big, and I guess it's a premium fruit for us and birds love that.

"You can get probably 20-30% of your pick destroyed by birds if you leave the netting up, so it's crucial.

"The netting comes up when we need to spray or if we have visitors, but otherwise it's down. Even if someone enters we ask them to put it down afterwards."

Costa horticultural manager George Jessett said the move to substrate started three years ago after seeing positive results from the method in raspberry production.

"That's becoming a very interesting and viable part of what we're going to do going forward," Jessett said.

He said the group tried to replant 10% of the farm every year, with around 60% dedicated to southern highbush and 40% made up of rabbiteye varieties.

Around 50 hectares of the farm's blueberries are under tunnels, and there have been significant changes in the proportion of production dedicated to the fresh market. The operation used to be 50-50 fresh to processed, but now it's about 90% fresh and 10% frozen.

"Evergreening and the ability to evergreen has probably been one of the things that underpins our success, and the real developments lately have been tunnels to mitigate against weather and rain, and then leading up to more recent developments of substrate production," he said.

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