In Clarks post Blackberries by the gallons
he mentions that his blackberries do a similar thing… i have grown (and am growing) his and agree.
Not to mention what Phlogopite explained.
Healthberry is somewhat uncontrollable and Victory is also in its own right… so the vigor demand i think causes the roots to form networks upon networks to ‘feed’ the top growth.
Victory turns everything into coffee ground looking stuff… or sawdust i reckon. So does healthberry… but healthberry becomes almost impossible to mulch after awhile as it becomes a thicket of nasty thorns.
I mulched Victory yesterday because i can see what looks like a spiderweb of roots poking thru that saw dust looking material… i mulched heavily last fall and its gone.
Anyways back to the story. My 3 test rows of Victory which turned out to be a permananent place was once a road so i mounded up some garden soil and then threw leaves and grass clippings on it for a solid year… in one of those rows i grew tomatoes for a year (that is supposedly a no no)… I then bombarded them with horse manure and woodchips that summer and fall… then went in the victory. Probably 50 wheelbarrows of woodchips and manure on those rows since i started them… and yesterday they looked like i had never done a thing to them. So possibly just a really healthy soil/compost that i have created a living monster with… or its the plant vigor that demands the roots to feed… or both.