They will bicker about whose spot has more sunshine, other tenants or neighboring kids will steal their tomatoes, someone will swipe the cute little solar spinning flower from one of the gardens, some tenants won't take care of their plots and they'll look like hell, some will use chemicals the other tenants will complain about, someone will steal the hoses.  

Before you start singing praises for certain companies and what they sell you might find this interesting....http://saferchemicals.org/newsroom/new-study-finds-toxic-chemicals-widespread-in-flooring-sold-by-top-retailers/

@Gary Hall it looks like my post came out far harsher than I intended.

I guess the worst case scenario with the garage would be someone using noisy power tools or stinky chemicals.  

Cleaning grease is a lot harder than I thought, special chemicals still require multiple cleanings...Moving the fridge was an eye opener as the floor was filthy with food grease and mouse droppings they chose not to clean. 

@Bret Allen We provide the house pest-free and will re-treat if reported in the first 30 days.Our lease has had the term "any additional or periodic pest control is the responsibility of the tenant" for at least the 11 years I've been here, and it has been vetted by our attorney.I understand your opinion may differ, but I would rather have a tenant raise the issue of being responsible for their own cockroach problem (we do SFH, so neighbors don't play in) than being named in a suit for damages because somebody had a fatal reaction to our pest control vendor's choice of chemicals. 

What about household chemicals which are considered toxic or flammable , will these be considered a breach of lease?

The enzyme products work chemically to change the urine into something that is harmless and does not smell bad.  

I personally don't use a lot of chemicals around my children & would hate for a tenant's family to be adversely affected by my pest control.

Certain chemicals can make the water unpotable.