Prohibit an existing tenant from having plants on the balcony?

[Kelly A.]

I have a tenant in a condo, and she is irresponsible with her watering of plants on the balcony, which may be affecting the balcony structurally (the board seems to think so, which may be the only relevant reality), and is definitely annoying the downstairs owner due to runoff. I've had this conversation with them multiple times, offered to buy saucers, etc., but nothing has worked. 

Can I prohibit the tenant from keeping plants on the balcony? The balcony isn't mentioned in the lease one way or the other.