Keep up with the fish if that is what you are using. From my observations in OR, Acer palmatums, as an example, in containers (and other Acer species in the field)start to harden/get woody/lignify? in August thru. September. There is a noticable caliper increase at this time (some "think" an increase in calcium happens at this time....calcium is taken up by roots via passive flow, you really cannot shove it into the plant. But if higher levels are available at this time,a noticeable caliper increase does/can happen).
Your winter comes earlier than here...start backing off or stop fertilizing mid to late August and induce some stress (slowly cut back on water also... this will help harden them up)

I have 'Neptune's Harvest' fish and seaweed liquid fertilizer and will use it once more at the begining of August because of it minor elements content.
Thanks for the tips.
Keep them coming
Paul