Depending on the lep, hostplants can be better for attracting butterflies than flowers. There are numerous leps that have no interest in flowers. I very rarely see red admirals or question marks on flowers but the males patrol my nettles almost every year.

Covering the plants in netting is a mixed bag because the mamas cannot get to them to lay more eggs. Covering individual plants that have pillars on them is doable with bags/sleeves but not something I usually do unless the hostplant is a tree or bush.

Wedding bags are a cheap way to go. Someone decided to start calling them organza bags and Kristi posted a company last year that sells them in a wide variety of sizes.

Organza bags for protecting cats outside