The first mishna in Moed Katan delineates limitations on agricultural work that may be performed on the less sanctified intermediate days of a festival (chol hamoed). The Shulchan Aruch (OC 537) codifies these limitations based on the principle of substantial loss (davar ha'aved), whereby which, if a field would be ruined if not watered, minor efforts are allowed to save it. How does this translate to modern applications of leisure gardening - e.g. of decorative flower beds or vegetable gardens that are grown for decoration or as a hobby, but not out of a financial need? If seeds planted before the festival would die if left unwatered, is that considered a davar ha'aved, even though there is no significant economic impact? Where is the halachic line drawn?
(These sites sound like they are lenient, but they do not appear to provide explicit sources or reasoning: