Trimming vals....

Why are you trimming them? The only time I touch them is when a "leaf" gets bad, then I snip it off as close to the root bunch as possible. I let them grow and bend at the surface (or go diagonal).
 
when mine get absolutely overgrown, i take them one by one (takes a while) and cut them at a 45 degree angle just below the waterline. a week later its time to cut again.
 
There are a bunch of different types of vals. The ones JR and i have are jungle and spiral. The spirals just grow about 6-8" and spread like weeds and the jungle grow 3-4 FEET and spread like weeds. JR has it right just snip at what ever height you want at a 45° angle. I tend to snip them at the base because the get too thick and spread too much. Last week I threw away almost 20 jungle vals that were no less than 2feet long.
 
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