How Does Your Garden Grow?: Root Rot

Mine apparently grows with armillaria root rot (aka "mushroom rot"). I planted 8 delicate bare root ball hydrangea plants about 6 months ago. As is my custom, I worried over them incessantly, watched them morning and night and watered them as necessary. One morning I came out and saw these little mushrooms all over the mulch and root area of the hydrangeas (I am getting chill bumps just thinking about this). I chalked it up to the goo gobs of rain we had been getting, pulled out the mushrooms and went to work. The next day, more mushrooms! Now I am standing outside in the 90 degree heat shaking like a leaf - what is attacking my hydrangeas?! And why are they wilting?

So, I googled "hydrangea and mushrooms" and what did I get? Armillaria root rot. The fun little fungus often hitches a ride to your garden from the greenhouses your plants are grown in. The mushrooms you see above the surface are the visible indication of the mayhem underground. Unlike the slugs I teased out and drowned with beer, armillaria root rot cannot be abated once it takes hold and it is fatal. Though I am devastated, the nursery I purchased from has a 1 year guarantee that they honored cheerfully. I received a full refund.

What I am trying to figure out now is what to do about my wilting hydrangeas and the soil they are in? The mint, basil, rosemary and cherry tomatoes are not showing any signs of root rot, so I don't think it's spreading. However, what steps should I take to safely remove and discard diseased hydrangeas? And how should I ensure the soil is ready to take new plants safely? Do I need to till the soil? Throw away my old gardening gloves? Help!

BEFORE:
Healthy, young hydrangea

AFTER:
Little mushrooms of death