I've recently bought a chipper /shredder as I want to make my own mulch.
I've been running green caña through it. As in picture it's like bamboo but not as strong, it's chipping up great and is perfect texture. My question is can I use it as is or should I leave it in a pile to go a bit brown first?
I agree with Tyler on the nitrogen issue. I use mulch wherever and whenever.
As a rule, I don't dig it in, and I try not to use things with allopathic properties. (Lots of walnut around here.) For stuff like walnut, I will stack it out and away and let it do its thing.
If you build beds with it or any other weed-like plant I'd cover it with cardboard or newspapers and go over it with wood chips or something. You can put it in a great big pile and leave it for a year or two, just keep adding to it. I've noticed that stuff like this can be piled four feet high and the next year it's almost gone.
Really, I don't think you have to get fancy. I have a fence-line with flowering bushes and small trees that have been planted over time. I started scything the fence-line last year and just leaving the weedy grass in place. It was like I put a liquid fertilizer down. Most of my trees have nitrogen fixers next to them, I just chop and drop.
That said I do have three running compost piles that I amend with kitchen scraps, this compost is for bed building. If you are just wanting it for water retention and slow amendment just pile it up around your plants and in your beds.
Just put the cards in their christmas stocking and PRESTO! They get it now! It's like you're the harry potter of permaculture. richsoil.com/cards