Yesterday afternoon, while I was repotting small crabapples in the nursery, I noticed more evidence of earthworm depredation. They had eaten many of the small roots or perhaps had eaten mycorrhizal (sp?) matter- in any case, the plants just pulled right out of the ground.
For the past 10 years we've been noticing some plants just pulling out the pots in the nursery with all the roots gone and I came to suspect earthworms sort of trapped in the pots with nowhere to go as they were on gravel- I figured that when they finished eating dead vegetable matter maybe they sweitched to roots. This has been wuite a problem with Heuchera and Tiarella- also I've noticed it with some Astilbe and Epimedium. When we visited Don Avery at Cady's Falls Nursery, he told us that Austarlian Jumping Worms (the worst kind) had eating roots of his Cypripediums to the extent that it killed them and these were in the ground. He showed us areas where there were many many worm castings. I noticed Monday, weeding at my house in my beds, where I have incorperated much organic matter over the 20 years I've been there, some of the plants - namely a Thalictrum just pulled right out of the ground when I was cutting off the dead stems and roots were gone (eaten by earthworms).
It is only very recently (this week) that I have started to worry about this.