I would if I were you, Iris can be quite ravaging if it likes the environment, a lovely plant but an evil one too...! For a 4-5 year old tree, last years crop sounds very large indeed. It might be worth you putting some sort of fertilizer down if you really want a bigger crop, but do make sure it's organic.
you have many options. fish blood and bone mix is probably the easiest one you are after. scratch the ground up around the tree, spread a few handfuls and water in. It probabaly won't get that far, but given it is an established tree you are going to have trouble with pretty much anything without damaging roots. you can get organic slow release feeds which release over the course of a year or 2, that perhaps should have gone in when the tree did, as it gives it a kick start to life. manure will seep down into the soil, but it really does stink, if you dig it into the top 6 inches of soil under the trees canopy and water every few days that should work. but it does stink so on your own head be it! you can probably find organic soluble feeds as well to put in a watering can and just give it a trickle of that every now and then - something akin to an organic version miracle grow. bear in mind just because it's organic doesn't mean it won't come in chemical form. there are plenty of organic fertilisers which have been refined and then look like any old treated chemical fertiliser, so do keep an open mind when you are looking for stuff.
I want to make a small spaghetti garden as well, but nobody around here sells spaghetti plants... Thy do sell plastic trees, though. But I don't really understand why anyone would want to grow plastic. It doesn't taste good TBH. *Slap!* Stop it!
Hey, maybe you can get an acrylic tree. No need for buying acrylic for modding when you can grow your own!
You should really get out in the wild more often. A trip to a local forest will probably help. Lots of funny plants and animals in the forest, you know.
