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Choose the biggest and healthiest rhizomes for your new garden.

I have trouble throwing away plants so perhaps you could find another area to plant smaller rhizomes.

The typical garden iris, German or bearded iris only blooms once in its short life. After that, it is a "mother" and produces new rhizomes only. This is why rhizomes that bloomed a preveious year are tossed out when the clump is divided. You'll know them because the "babies" are large enough to be separated from the mother. Use a sharp knife to do this. Add compost to the soil and prepare the hole. Make a mound in the center and put the rhizome on top. Spread out the roots and backfill the hole. The rhizome should be half exposed - above soil line - from leaf end to tip. (You may need to cut the leaves in half if the rhizome keeps tipping over.) If you do this, your flower stems will go straight up if they have enough sun.

Cutting them back won't stop the leafy growth. When other plants lose their leaves, cut them back to 3-6 inches so they look tidier over winter. Make sure to pick up any iris leaves that have dried and fallen on their own. I don't believe this surge of growth will harm the plant at all. That rhizome stores a lot of energy! I think your iris is simply saying "Whew, a break from the heat".

This seems like a lack of nitrogen, as this can cause yellowing leaves. I would recommend an all purpose fertilizer. You can cut the iris, or you can leave them. Either will be ok. Here is an article that will help: https://www.gardeningknowhow.com/ornamental/bulbs/iris/iris-plant-care.htm

I'm sorry but they will be too far dried out to plant

Yes... That is typically a good time. When the ground can be worked, then they can be planted. They are actually Pretty cold hardy, depending on the cultivar, but they will do best if wintered indoors until you can plant them. After that, they will survive, completely, on their own. In fact, you will find that over a year or two, you might need to "thin the herd" a little. They will multiply!