I had one that you stick down in the soil, but that didn't seem accurate at all plus once roots were forming, I didn't want to stick anything thru them. This one saids to use soil in a little vial, but I test the runoff with it. I don't know.. maybe that doesn't work right either.. Never even checked ph a few years ago when I first grew a couple of plants. I guess I just got lucky cause they turned out great. It is a WEED for petes sake..I usually have no trouble growing weeds.lol.