Auto Plant waterer

Well things have certainly been quiet round here. Has everyone gone to Facebook? Let's get posting again

Today I made a 555 circuit to automatically water my chilli plants. It's not finished yet, I'm just testing if it switches on/off reliably when the compost dries out and rewets ️
No it never switches back on until the compost is about 500k ohms. Compost is quite dry at 150k ohms and wet through is about 20k ohms so I've changed a resistor (I may fit a multi-turn pot later) hooked a submersible pump up and testing what is a fully functional prototype...
Works for a while until ions build up on the sensor anode and rots it off (electrolysis)
Think I'll have to use a graphite rod as a sensor