Worms can live very happily in hydroton or gravel or plastic mesh and plastic drink caps and bits of cut off PVC even. They need it moist and as Vlad says, worms can even live under water as long as there is good aeration of the water. I've found worms living in my pump trap even.
I have been using worms in my system for a while now....after changing things around recently I noticed 2 tomato plants in the gravel that had been thriving suddenly get all droopy and lousy looking.....while several other directly adjacent were fine........I scraped back gravel carefully to examine the roots.......there were a zillion redworms apparently munching on the roots of these 2 specific tomato plants.
Apparently the worms needed more food than they were getting from the fish waste solids. I drilled holes in a snap lid Folgers 2lb coffee can ( plastic) buried it 3/4 of its height into the gravel,filled it with coffee grounds and some scrap veggies........popped the plastic lid back on it........and waited.
I also uprooted the problematic tomatoes, washed the worms off the root structures and moved them to a slightly different area of the grow bed .( the washed off worms went into the folgers can on top of the coffee grounds)
Long short, the problem is fixed, the plants all perked up, and the folgers can is filled with worms......they basically found their all you can eat buffet........the snap lid keeps the other evil bugs from getting the worm food
Supplemental feeding is a good thing to keep them from chewing the roots off your plants if they are hungry......but each flood and drain cycle also floods your system with worm tea, adding nutrients to the whole thing...
I think lest anyone think that they may be adding a problem to their mediabeds by adding redworms, we need to clear up a few things.
Redworms are secondary decomposers. They do not have teeth. Not capable of chomping anything. They rely on symbiotic microorganisms to first work on whatever they are going to eat. The redworms will then consume matter. They can only consume dead or dying/decaying matter.
In short, my conclusion is that yes, the redworm probably really 'enjoyed' the treat you gave them. Like giving kids open house at a candy shop. But it would be important for you to look at the health of the root systems of your tomato plants. What did they look like before you washed them off? Something is going on there. It may be that you have some sort of mold, bacteria,slime, or the like that is first moving in on the root systems, which will cause plant health problems. The worms are just moving in to eat away the problem, and the dead/decaying roots.
I am glad your plants perked up.
I agree with converse.
Perhaps the location the tomatoes were in had become too root bound or was staying too wet for the tomatoes or something like that but the worms themselves wouldn't be causing the plants to do poorly, the worms were probably only there slurping up the slime around the roots, dead and decaying roots attract worms.
Could be , on both counts. but the root structure didn't look slimy or moldy......it definetly wasn't root bound....
The tomato was doing well one day......the next day it looked horrible. this is an adult tomato plant setting flowers etc.
What it looked like, was that it was dehydrated....horrible leaf wilt, and droopiness.dug down into the gravel to make sure it was getting water up to the root structure ( I've been doing new stuff all over the greenhouse so I hadda check) everything was good. You could see the water had been coming to within 3" of the top of the bed, then draining.
So, I was gunna pull the tomato, and put something else in there....when I popped it out...the whole root system was alive with red worms.....like a bad movie... I shook off as many worms as a I could, then rinsed the rest off in the return trough to the fishtank...........decided it may have been the worms, and replanted it into the gravel again, in a different location....well, a week later and its doing fine...maybe there was crud on the roots the worms were eating.I have no idea........maybe the rinsing washed away whatever that crud could have been.I don't know....
I had a similar thing happen in a container tomato (in dirt) last year, and it happened after adding castings I knew were full of eggs and some immature worms...so I kinda did the 2+2 thing on it being the worms causing it