All of my trees are in pots. Something has been digging the soil out from under the trees via the small drainage holes. This happened in two pots so far. The drainage holes are about an inch or so at most, yet most of the soil has been removed through these holes. The top soil looks normal until you see a mound or dirt next to the pot. When I jab the soil in the pot with a stick, it sink holes and reveals the empty cavity below the soil.

My trees are on a rooftop deck which , to me, would make it very difficult for rodents to get to. I've never seen any rodents there. The only animal I've seen up there are scrub jays and other types of birds. I haven't seen any type of nest, eggs or anything resembling baby creatures in my carved out pots. The two pots were roughly 15 and 20 gallon sized.

Any idea what did this and why?

Put out some snap traps set with peanut butter. You may indeed, be having mice or voles (the only rodent I know small enough to get through the hole on a bottom of a pot). The other possibility, but less likely would be gophers. But, they couldn't possibly fit through the bottom of a pot, and being on a deck, far less likely.

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7439.html

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74161.html

And, don't think you don't have rodents in California! They're everywhere. I'm pretty sure you've got mice, and they're looking for a burrow home, and your pots look enticing to them. So, set out some traps and see what you catch.

Thanks for the suggestions. I read the links you provided and I think I can rule out voles since they said they are poor climbers and don't usually enter buildings. I've thought about mice but I've never seen any droppings anywhere. Plus, I don't see any evidence of their other behaviors such as chewed up or shredded anything.

Any other suggestions would be appreciated. I'll hold off on traps for now and see if it happens again. In the meantime, I will keep my eyes open.

I have had troubles with rolly pollies/ Potato bugs.. they would clean out the soil from the drain holes and make pockets of air in the pots.. also slugs and snails... I'd look for these bugs getting in your pots from the holes.. they like to eat roots too!!!
I put cut potatoes on the top of the soil to draw out the bugs and wash them off with HOT water and replace the potato.. reuseable bug catcher!! just besure and not forget it is there you might end up with a potato growing in your citrus pot..

Gina *BabyBlue*

I've never seen any rolly pollies but I have seen things resembling snails or slugs. I usually find them in between empty pots stacked in each other or on the bottom, usually where it is a little moist. Interestingly enough, I haven't seen any in either of the two affected trees.

What scares me is the part where you say they like to eat roots! One of the trees that this has happened to is my Fuji apple. This tree didn't put off any leaves last year and now I'm wondering if its still alive. I pruned back the branches after I repotted it and the branches were a dry brown. No flexibility to the branches like I see on the bare root ones at Home Depot.

What's even scarier is that the second of my trees that this has happened to is my prized (approx) 20 in 1 citrus cocktail tree. I'm hoping that it doesn't die.

I haven't done any research yet as I've just read this post, but what's the easiest and safest way to get rid of slugs/snails in the soil without harming the tree or affecting the edibility of the fruit?

No, snails and slugs will not do this kind or soil removal. I, unfortunately, am the "Queen" of snails out here in S. California. This is not your issue. You would know for SURE if you had snails by their slime tracks, and your trees would have big holes eaten out of the leaves. Plus, the snails will "sleep" under the leaves, underneath the rim of the pot, or under the pot. If you are concerned about what is going on inside your pots, instead of trying to guess, I would suggest you pull your trees out of the pot, and see if you can find any bugs, mice, etc. in the pot or soil. That way, you'll know for sure what's going on, instead of just trying to guess. As well as identify whether or not your little apple tree is still alive. To treat snails/slugs you can use any number of products. Metaldehyde is the most common snail pesticide, but it is poisonous to humans and dogs. I do use it on my citrus trees outside the fenced yard (front slope), where my dogs can't get to, in the form of pellets. For inside my yard, I use Deadline, which is liquid metaldehyde and make a ring around the trunk of the tree. I will also use Sluggo (iron phosphate), which is organic, not attractive to dogs, and works fairly well. If you use Sluggo Plus, that product contains both iron phosphate for snails, as well as Spinosad, which will kill pill bugs (rolly pollys)

what about earthworms , I have problems like that with them

It would be very unlikely to have earthworms in your container citrus unless you used your garden soil for the containers (not recommended). And, they certainly would not harm your tree's roots in any way. A LOT of earthworm activity can leave piles of chewed up dirt and castings, but those are a good thing. I can't imagine what this forum member's issue is would be caused by earthworms.

I placed my trees on a concrete in the garden and once I got them inside I noticed that something is moving the soil out and one day when I raised the pot I saw an eartworm

Well, that would be one very adventerous earthworm, to be able to leave your soil, crawl across the concrete, then up into the pot! Did you use a bagged container potting medium, or did you use some of your garden soil for your tree? Or, possibly transplant the tree from the ground to a container (thus taking with the tree a little hitchhiker in the form of an earthworm)?

well that concrete wasn't that big ,just 2sq feet and was at the same level as my garden is and on rainy days they can travel and because I didn't had any tray underneath this is what I got ...

Earthworms can eat any roots, if find nothing else to eat.

Snails are food for lizzards, frogs and toads.

Yep , you're right but since citrus trees can go well on the dry side and have no problem an earthworm won't like the soil being dry so they go out in the tray were you can collect them by hand

Then they would not even go into the substrate ...

Maybe they just wanna see another world ...

I just remove them at repotting and since I do a lot of compost they seam not to eat the roots.