If you could kill Siberian iris with wood ash, or any other relatively non-toxic substance, I'd know about it. These plants seem to be indestructible! While they prefer acidic soil, you'd have to apply a fair amount of wood ash to actually make them unhappy, unless you're starting with alkaline soil - they prefer it to be between 5.0 and 6.5. If you know your ph, approximately, you'll be able to tell if you've really applied enough to make them sulk. If you're worried, you can make sure they get lots of water this spring, that will wash the ashes through the soil; you could also add some aluminum sulphate, I suppose.

What zone you are in? Are the plants dormant now? I'm not a sage expert but in general... When you move a plant, digging it up causes loss of root mass. This means the plant has a more difficult time taking up water. Frequently plants wilt under this condition. Relatively speaking, a small number of roots cannot take up enough water to support a large number of leaves. When this happens, it helps the plant by pruning it back after the move, equalizing root mass and leaf mass. I've done this before and the plant stopped wilting and recovered. The next year it was full and looked great. So based on that, it may actually be easier on the plants to move them now before there is a large number of leaves. You shouldn't have a problem with wilting. Just my opinion.

Tomatoes are virtually impossible to kill once they're going. Seriously, as long as you've got a couple inches of green, you can regrow the entire plant. If its got any roots left at all, it'll be fine in a few weeks. Last year I had a windstorm that knocked one of my container tomatoes over, rolled it around, snapped half the thing in two. I just stuck the broken limbs in some dirt in a bucket, and not only did the limbs survive, they went on to bear fruit the same year. Heck, several of the limbs had tomatoes still on them and not only did they survive, not only did the tomatoes not wither up on them, but they were even GOOD tasting tomatoes at the end. Basically, nothing short of weed killer or ripping it up by the roots and tossing it on hot asphalt will kill a tomato plant.

I grow mine in a hanging basket.I grow mine in wire basket with cocoa liner.so it actually gets 'air pruned'meaning its roots are pruned by being exposed to air.I have not trimed their roots when planting.I added a variegated one this year from a 8 inch pot.I had moved it up to a qt pot for 2 months before planting in hanging basket.I DO understand your meaning of the roots and space.I spread them out when I plant& was a time adjusting it level wise. I think your plant may be fine as long as still had plenty of roots to support the size of the plants current size.Mine bloom from late may-june all the till bout January.I stop watering when last buds have opened to let it go dormant.My one is just wakeing up again now.