Iris are generally planted 12 to 24 inches apart. Close planting gives an immediate effect, but closely planted iris will need to be thinned often. Plants spaced further apart will need less frequent thinning. Many people plant them in small groups of say, three or five or seven; to give a massed effect. Newly set iris need moisture to help their root systems become established. Specific watering information depends on your climate and your soil, but remember that deep watering at long intervals is better than more frequent shallow waterings. Once established, iris normally don't need to be watered except in really dry areas. Overwatering is not desirable, but many people make this mistake. Specific fertilizer recommendations depend on your soil type, but generally an all-purpose food or a 6-10-10 are the way to go; just keep it low in nitrogen. A light application in the early spring and another application about a month after bloom is a good idea. Avoid using anything high in nitrogen, as nitrogen encourages rot. You can also give one more light feed after the growing season in order to encourage healthy growth for the next season. You will need to divide your iris before they become overcrowded, generally every 3-4 years. If too crowded the bloom will suffer, some varieties may crowd others out, and disease problems may be occur. Old clumps may be thinned by removing the old divisions at the centers of the clumps and leaving new growth in the ground. Or, you may dig up the entire clump and repalnt wiht the smaller, new, and healthier ones.

Along with your criteria of low maintenance, high privacy and very inexpensive you may also want to consider using plants that are practical around a swimming pool, this means plants that are relatively clean in regards to shedding or have large leaves that are easy to pick up and won't clog an intake filter like lots of small falling flowers and leaves do. Several palms are fairly clean in regards to shedding and can give you some privacy. As far as the expense goes, I suppose that is a relative term. Some varieties to research would be Trachycarpus fortunei, Chamaerops humilis and Syagrus queen palm. You could do a dense planting of cannas between the trunks and might even have room for some succulents. If palms are not your thing then you might consider some large espalier type trees such as Magnolia little Gem or possibly some narrow growing hedge plants such as pittosporums or podocarpus I think it would be a good idea to visit your local nursery and see what they have to recommend for your particular neighborhood/ climate zone.

The FAQ has some suggestions... Keep in mind fast growers are not always the best choice if they are messy and/or have invasive root systems. Check with a good nursery about leaf, fruit, and flower drop as well as what the root systems will do to the surrounding areas. Here is a link that might be useful: screening suggestions from FAQ

If that is indeed a willow, you can tell from the size that it has been there a long time. Certainly long enough for any issues to have had time to manifest. While I would never recommend planting one that close to a structure and any plumbing access, it is what it is now :-) I would also recommend some sort of drought and shade tolerant evergreen groundcover. If in Vancouver BC, there are lots to choose from.