Triple Crown blackberry project

General Fruit Growing
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I’ve found this site useful for starting my own little berry experiment in my backyard, so I thought I would give it back and document my triple crown thornless blackberry project. I have some other berries but they aren’t as well established so I will wait to evaluate them. Early last summer (2020) I planted 3 TC blackberries 4 feet apart against my western fence (berries face east). I put up an “I” trellis with two wires at about 3 feet and 4.5 feet from the ground, strung between two round tree stakes pounded in. I had weaker wire previously and switched to 16 gauge galvanized steel which stays taut and seems more supportive for such a monster. The berry patch gets sun from early in the morning until about 2 pm, and the higher foliage gets sun nearly all day.
Last year the plants sent out primocanes along the ground that looked more like trailing berry vines. We had a weird cold snap in early October that got down to 12 degrees F, turned out to be the coldest temp of the season, oddly. Not too cold for blackberries but the timing seems like it killed tips of some of those canes. This spring I cut the dead tips off, strung those canes up and the laterals grew vigorously and now have quite a bit of fruit on them. This spring new primocanes popped up and also grew very well. I just tipped some of them and the laterals are now sprouting out at an alarming rate (maybe I should have delayed tipping till later in the season to keep the laterals from growing too vigorously?). I hope the SWD scrouge is not a huge problem here in Eastern WA with the cold winters and arid summers, but we’ll see. Pretty decent crop coming up.

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I got a little obsessive arranging these primocanes neatly along the wire

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Looks fine. Tipping should be done at the desired height regardless of the date. TC laterals tend to grow at various angles from nearly horizontal to over 30 degrees from horizontal, so the top laterals may end up some feet above the tip point. Those arching laterals need some support or they will come over sideways under fruit load. If you find the upper fruit getting too much UV damage then prune the whole thing to stay lower in succeeding years. Let the laterals grow into October before pruning to length otherwise your laterals will have laterals that may not produce full-sized fruit.

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Right on, thank you for that insight. You think I should just cut out any additional primocanes this season that don’t fit nicely along my trellis? Seems like 5 or so canes with this arrangement will be plenty.

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With your very short TC row, the compromise would be either keep all primocanes and do the final lateral prunes quite short, 3 feet or so, or reduce the number of primocanes and let the laterals go several feet. The total lateral footage being roughly equal for either case.

The very first consideration is how much fruit do you want. A decent TC crop will produce multiple pounds per cane.

I would let all primocanes grow until October to assist in root development, and then prune off any unwanted canes.