We own a landscape company and we wanted to use photos of landscape jobs we've installed and photos of gardens we have planted. Do we need permission to post these photos we've taken on our website?
In the United States, this falls into the gray area of "you might need a property release" (which, to my knowledge, has never been tested in court other than with buildings that are trademarked).
The best solution is to likely include a photo release as part of your standard contract; buyers likely won't even flinch and you'll be protected from a legal standpoint.
Disclaimer: I am not a lawyer, consult one if you want advice that's more accurate than an internet message board.
It is not a question of rights, it is a question of common courtesy.
It is courteous to ask, and if refused, to respect their choice, after all it is their property.
Put yourself in their shoes. Do you really want photos of your garden used in some company's publicity work? Perhaps you do or perhaps you don't mind but you would definitely expect them to ask first, as a matter of respect and courtesy.
Just to extend this answer somewhat. People in their private homes have strongly held ideas about privacy and we have to be careful to respect that. The concept is enshrined in the phrase "An Englishman's home is his castle". See also this reference.
William Pitt (in 1760) said "The poorest man may in his cottage bid defiance to all the force of the Crown. It may be frail, its roof may shake, the wind may blow through it. The rain may enter. The storms may enter. But the king of England may not enter. All his forces dare not cross the threshold of the ruined tenement."
In Germany: if you can't take the photo standing on public property (without aiding devices like ladders), then you would have to ask. See Panoramafreiheit (in english).
I'd say, yes, for the rest of the world too. Put your right to publish a photo of your work in the contract.