don't go too acidic or basic and don't clog your soil up with sugar. dry spices would be your best bet. i wouldn't try it on an entire garden either, just a couple test plants. i imagine it's been tried before and unless it's being kept a secret, it might be more trouble than it's worth. as you're keen on strawberries, that's a good potential flavor. you might try freeze drying strawberries to grind them into a powder, or maybe putting a piece of strawberry candy at the very bottom of your pot where it at least won't choke your soil. if they weren't so acidic, kool air flavors would be cool as they're easy to dilute in water. the easiest thing to do though is just to pick strains that have natural flavors of their own. after that, spices seem like the best candidates, though many of those might have pH issues too. a little should go a long way though i'd imagine considering that less than a pinch of chemical ferts in a pot can throw flavor.
cinnamon is about the most delicious spice if you ask me, but you could also try coffee beans i guess. i don't know how they'd affect flavor, but i bet plants would love nuts. i bought some vegan ferts that had all kinds of seeds in it, possibly even sunflower seeds without looking.
try looking the subject up with a search engine to see what, if anything works. it might not help the flavor much, but i bet plants like carrot juice to build off.
i still like the idea of cinnamon as it's a dry spice and a very distinctive and string flavor. dried pepper woul be a second choice and maybe garlic, but you could try any spice you like like greener ones such as thyme & oregano. i bet the licorice taste of anise would pass too if the tech actually works, but after trying real durban poison, it's not the funnest flavor to smoke. maybe cocoa powder would work too.
this is all theory though until you read up on someone that's tried to artificially flavor MJ.
i was just trying to find more info on the subject, and so far, the general consensus is that flavoring your soil is bunk, but you could always add flavor after the harves eg, putting cinnamon sticks or dried orange peels in your jars while your buds cure and passively absorb the flavors. you could even get away with using kool aid etc. that way as the plant is already dead when you're curing. you just wouldn't want to physically get any powder directly on your buds.
getting a flavor strain to begin with and feeding it organics under a full spectrum is the best method. all kinds of stuff can happen to growing plants when you mess with their chemistries.