Who did the installation? I assume that your irrigation system is tied to your domestic water and its city water provided, no well. More details would be helpful. Do you have a basement or slab, etc.
You need to know where the irrigation system ties in and it needs to be replumbed to before the water softener. Whomever sold you this or installed it do know that you cannot irrigate with soft water but most salesmen or reps will never tell you what you cannot do. Do not water any house plans either. Plants do not like ion sodium water. Ion sodium water is soluble, that is why your soaps usage should be cut in half such as when doing laundry.
From a google search:
Hard water... is water that contains an appreciable quantity of dissolved minerals (like calcium and magnesium). Soft water... is treated water in which the only ion is sodium. As rainwater falls, it is naturally soft.
I had one installed in 1981 and fortunately I had a basement. I reran pipe to the outside spigots except the one in the garage. Washing your vehicles with soft water will never dry with spots, It's great.