I wanted to put up a washing line post in the lawn. I have zilch experience. I dug a 20cm square and a 50cm deep hole. I filled it a third with water and put the plastic pole socket in. I got the post crete out the garage and it was rock solid. So I whacked it loads with the spade to make it loose and spent an hour filling up the hole, handful by handful. The water level just kept rising. So in the end I gave up. I stuck the washing pole into the socket and shoved loads of the dug up mud into the hole.
So, have I made a complete hash of it or do you think it might be stable enough for the weight of the washing?
I'm feeling exhausted now so hopefully it's turned out ok!!!
Ideally you would dig the hole to the size you need, fill it with concrete and put the spike into it so it sets. This will ensure your washing line never falls over but if you get it wrong its a pain to dig out all the set concrete and smash it off the spike.
Personally you can buy these metal spikes that are probably better than your plastic one - B&Q etc. will sell it so just pop in and ask. You simply just hammer them into the ground no concrete no digging a hole.
I bought a new post at the weekend and spent a tenner on a post screw which you just screw into the ground - has a little bubble on it to ensure it is level and then post fits straight into it. Well easy and no concrete involved!