Other than the obvious "Don't"?

I'm working on connecting the shower and rinse water sink in the kitchen to a branched drain system to water some more fruit trees down in the garden.  To simplify filtering, I'm leaving the wash sink with all the grease/food particles connected to the septic tank.

My issue is that I produce much more grey water than the trees need during the winter (10-15 gallons surplus per day), and not nearly enough during our hot, dry months (May and June). 

I'm planning on building a subsurface flow constructed wetlands to process the shower and rinse sink water.  I'm wondering it this will purify the water enough to allow storing it for up to 6 months or if I'll need to additional purification.

Any thoughts?

FWIW My eventual goal is to expand my rain water collection system to the point where I can disconnect from the water company.  Having a more efficient greywater system should help during the occasional long dry spell.

Trying to store greywater is considered an error, because it will quickly turn to black water:  http://oasisdesign.net/greywater/misinfo/

The grownetwork has the water harveting expert Brad  Lancaster speaking on harvesting greywater. It's a free webinar, starting Monday, June 12th.
http://thegrownetwork.pages.ontraport.net/hgfs2017register
Our fearless leader is presenting as well!

Maybe Lancaster will touch on storage?

If you are filtering it subsurface, I suspect we could say it's no longer greywater but rather groundwater.
Maybe it could be passed through the subsurface filter into a retaining pond. Kind of how  a natural swimming pool works.Plant the pond with duckweed.
Use a solar powered fountain for aeration.

I know that septic systems that do not percolate up to municipal standards use a peat moss system. It creates an affective bio filter for septic waters so i imagine that it would handle gray water.