I know to 2 methods, chop stick and sticking your finger in the soil to see if its still wet. My problem is that my tree (I believe) has regular soil and its pretty hard to stick my finger thru the soil because its so packed, not to mention when I actually get my finger in the soil it gives mixes thoughts because the soil is so cold it feels wet but I'm not sure it actually is. I read earlier that soil can appear wet but it mag actually be drying out underneath which is why I'm checking it. I placed a wooded skewer in about an inch, I'm supposed to let it sit for a while and check it like a dip stick...I'm assuming the wood will be a darker color if the soil is in fact wet, correct me if I'm wrong.