Arduino Controlled Grow and PC Program - Work In Progress

Nice work - and good hit on the one-wire. I've been planning on using one-wire for temperature and recently found ones for humidity. That and an LCD screen for the local-access - and maybe an ethernet shield for remote as well. SSRs

For the relays - if you run them well under capacity you should be fine. Also if they're rated for motor start the specs will tell you - that is if you can get specs.

If you switch to SSRs be sure to properly heat sink them. Perhaps more a note to others that might not know. That 30A SSR is probably only rated at that with a decent heat sink. Not a bad deal - but it's probably only good for 5A (100% duty) w/o heat sink. Also for SSRs (which I didn't see in your wiring box photo) remember that they also can fail shorted / closed circuit. In fact - I've had two PID controllers on epoxy curing ovens go open-loop. Alarm lights blinking on the controller all the while the embedded SSR was letting everything run. Not fun when the wife mentioned "Honey, you might want to look at this, you've got smoke coming out of your curing oven" Too close to having a fire. Fool me twice and now I use a water heater safety thermostat. If you look at your top element - there's an extra red button. That is a 180F safety cut off. If it cuts off - it requires manual reset. Since it's not normally switching it doesn't wear out either. Good safety. And still it's tripped for me too - like when I was too clever and added a 7W "always on inspection light" that - very slowly - got the temps high and the PID controller wasn't in that loop . Look for all traps! So relay or SSR - anything with heat add something with a manual reset hard cutoff. If you want - put a very low wattage bulb in parallel with it and it'll be your "oh-crap" indicator

Good work - and keep it up. At this point I'll probably end up using 80-90% of your work.

Great thread man, really selfless stuff you're doing for others - great karma to you, friend