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lemons in the greenhouse

March 2022 - Brix for Citrus: A tool for fruit quality assessment

Figure 1. Robertson and Trovita Navel Oranges in the greenhouse.

I subscribed to Citrus Industry This Week to keep up with Florida’s citrus issues. Times are tough for Florida growers. The disease Citrus Greening is having a devastating effect on the production and quality of oranges. Growers are having a difficult time even meeting the industry standard Brix requirement for oranges of 10.5%, and for grapefruit, 7.5%. For the first time that I’m aware of, on February 4, 2022, the Brix standard for oranges was lowered to 8% in response to citrus damage from a late January freeze as an emergency measure. Hard times. Don’t expect Florida oranges to be bursting with flavour this year!

Figure 2. Late January 2022 freeze causing severe crop damage in Florida.

Despite the difference in latitude and climate, my British Columbian trees tend to follow similar ripening periods as Florida and California. I thought it would be interesting to see if my oranges and grapefruit could meet the Florida standards despite minimal heating and no supplemental light. Here’s a table showing how the fruit rated during the 2021-2022 season which has now ended. Testing was limited to the fruit showing results on the specific days.

Figure 3. Brix readings for The Garden's winter citrus season.

I’m excited that the Washington Navel orange met the Florida Brix standard of 10.5% during the latter half of its season. Oro Blanco and Cocktail grapefruits are also doing well in the greenhouse. They have great flavour, production and consistently exceed the 7.5% standard.

Part of the impetus for this leaf sap study is to see if I can increase the quality of Robertson, Trovita and Cara oranges with improved management informed by the insights from plant sap analysis. Over the years, their fruit has been flavourless and tended towards a granulated texture despite being treated the same as the Washington Navel, which is consistently juicy and delicious.

Recently, while speaking with another grower, the topic of navel orange fruit quality came up. It hadn’t occurred to me until then that my Washington Navel is grafted onto Flying Dragon rootstock. The other grower confirmed that his orange trees with Flying Dragon rootstock outperformed his Trifoliate grafts. Trifoliate is the rootstock for my three lower Brix navel varieties.

Despite this new insight, I have seen an improvement in all the oranges this year, most notably in the reduction of granulated flesh. I will continue to monitor their progress and hope as the soil improves their flavour will as well.

Figure 4. March 27, 2022 - The last of the navel oranges for the 2021/22 season.

Checking out their Brix levels.

Today, March 28, 2022, I picked the last of the oranges to measure their Brix for this blog. The Washington was a delight to eat. The last Trovita fruit hidden amongst the branches was under-ripe but flavourful. The Cara Cara flesh had a light pink tinge and a delicate flavour. The Robertson flesh was almost tasteless but its intensely aromatic peel will be perfect for candying.

The days are now lengthening, and I see tiny citrus flowers emerging in the new growth; a happy and hopeful wish for a good crop this coming winter.

This project is supported by the Canadian Agricultural Partnership, a federal-provincial-territorial initiative. The program is delivered by the Investment Agriculture Foundation of BC.

Opinions expressed in this document are those of the author and not necessarily those of the Governments of Canada and British Columbia or the Investment Agriculture Foundation of BC. The Governments of Canada and British Columbia, and the Investment Agriculture Foundation of BC, and their directors, agents, employees, or contractors will not be liable for any claims, damages, or losses of any kind whatsoever arising out of the use of, or reliance upon, this information.


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