Marion Berry in Illinois
I have Marion Berry Caine’s which will be in third year in 2018. They produced in 2017. Last winter I protected them with enclosure on ground and heat cables to keep temp above 30 degrees. What would be an alternate winter protection regime for my area? Same weather as St Louis. Thank you, Ron Gray
Richland County Illinois
Thank you for your Marionberry question, Ron. (This blackberry cultivar was developed by Oregon State University, and are named after Marion County, Oregon, where 90% of them are grown!) These training blackberries are a very special berry!
If you are in the same USDA zone (7a) as St. Louis, you have similar historical low winter temperatures as in Southwestern Oregon, so this Extension article recommends: "In western Oregon, it’s best to train the new primocanes on the trellis in late August. The risk of cold injury increases if you wait to train in September through fall. In eastern Oregon and Washington, leave the primocanes on the ground. In areas with frequent low winter temperatures, you can try to protect the canes through the winter with a straw mulch. Then train the primocanes onto the trellis in late February, after any danger of severe cold has passed. Training canes during cold temperatures is not advised, as brittle canes break easily." (Some resources indicate that these canes can even tolerate temperatures in the Zone 6 range--down to -10 degrees F--so long as you have trained them as indicated above.) But a straw mulch would be easier and cheaper, and conserve electricity.
Hope this is helpful. Good luck!