By Floydd
United Kingdom 
I have just planted 2 castor oil plants into 2 tall tubs
and something is digging in them overnight I planted 5 other tubs with various plants and seeds these have not been touched all in the same area yesterday I emptied them both found nothing and replanted with some slate and pebbles on top this morning they are covered in soil again
16 Oct, 2014
Answers
thanks I thought that why target these 2 not the others which were easier to get to ? yes they are Fatsia japonica
16 Oct, 2014
Mice burrow for various reasons. They could just be finding somewhere to bury seeds for winter rather than digging for something.
16 Oct, 2014
could also be squirrels at this time of year.
16 Oct, 2014
I have also seen magpies dig holes in pots to burry food to eat later.
17 Oct, 2014
'easier to get to' could be your answer. What looks easier to get to to you may be more exposed to whatever creature is doing this. Hence the untouched pots.
Plus, of course, the animal is not seeing the garden as you do. If you've put these pots in a place where something is passing by that's why they are getting dug up. The creature will not look around to see what else is available.
18 Oct, 2014
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Could be a mouse. You say Castor oil plant...I take it you mean Fatsia japonica (false castor oil plant)? The former is not frost hardy while the later is.
16 Oct, 2014