If a garbage disposal stopped spinning but makes a bit of noise showing the electricity is on (likely something is blockage it but unsure), who is supposed to pay for the technician to repair it: the landlord or the tenant?

Put a grate of some sort on that intake so that doesn't happen again, pay for the repair, then let the tenant know that if there is every a blockage of that intake it will be their responsibility to pay because that is a result of them not maintaining the grounds.

Changed the lease to basically say that as the owner I am responsible to ensure operational status of all the facilities and, at the time of your occupancy, electrical, heating, cooling and all plumbing fixtures are operational.If there is any blockage of the plumbing, it is due to your negligence and therefore your responsibility to have it cleared. 

Of course, if it's something other than just a simple blockage or there is damage to the line it will cost moreI've never heard the term hydro scrub. 

The professional plumber said the tenants are causing the blockage, so that's all the evidence you need.

So, if there is a blockage of the openings beneath that bleach dispenser, the rinse water can't drain through and you end up with water on the laundry floor; obvious solution is to clear the blocked openings beneath the bleach dispenser on a regular basis.

They found feminine products which caused the blockage. 

If a pipe freezes, it is actually the pressure that is created between the blockage and the faucet that will cause the pipe to burst.

Take out the hedge as Nicole suggested because it creates a visual blockage to the front door, but you also need to widen the sidewalk to make your entranceway more important.  

Routine issues such as a clogged drain, the plumber should report what he pulled back, if anything, and how far out was the blockage.