ELECTRONICS: PLEASE HELP - Plant moisture sensor not working - or is it me???

Can anybody PLEASE help, I am in the UK and eager to grow melons next spring. I need to know when the roots of the tub need water so decided to make a moisture sensor. I found a ‘plan’ online, bought about £20 of components (I need to make  two sensors) and have spent all afternoon TRYING to get the online schematic to work. One attempt was connected via a circuit board and the other in air connections. Neither attempt works, the LED comes on on both attempts but does not go out when the terminal probes are put in water, as they would when the plant roots are moist.

i enclose the original internet schematic and a (poor) picture of my ‘‘air connection’ version....should this plan work? And if so, why isn’t it?

thanks in anticipation

If you want to use such a simple sensor you might as well use your finger - or get a self watering pot until they go in the wild.

TN1946 (author) 20 days ago

Here are the pictures - internet plan and air construction -