Thanks Baja, for starting this thread.
My watering approach is primarily based on the fact that I have too many plants and too little time to water them by hand using the more dedicated plant dependent approach. This on occasion costs me a plant that is unable to make do with my unified approach, and then I kick myself for a few days, before moving on. I tried hand watering with acidified water but at the moment in my life I just do not have the time - I wish I did.
I water by hose with tap water (which comes out around pH 8), which has a chlorine filter on it. I have recently switched to a shower head style attachment which has a gentler, but larger flow of water. I am still figuring it out. It has the advantage of dispensing a large amount of water quickly but at lower pressures, which speeds up water and is supposed to disturb the soil less, however with pumice rich soil mixes (same would be the case for perlite), the amount of water that accumulates in the pot does get the pumice floating a bit. I think the solution to that is to water from slight higher above the pot which in my most recent watering appeared to avoid this.
My collection is mostly made of cacti, agaves, aloes, with a sprinkling of other xeric plants mixed in (Adeniums, Euphorbias, Fouquieria, Sansevieria) all plants are kept outside year round (my SO is the house plant person, though we have some Sansevierias, Haworthias and a cactus or two on a bright window sill, where the two plant collections meet).
I live in the middle of the Greater Phoenix area heat island, so while officially my zone is 9a/9b, in recent years, it has mostly been 10a, with the occasional around freezing night thrown in in winter. It does mean that the summers are really rough on many plants if not provided a good amount of shade, which since moving to a new house has been somewhat of an issue. It has also meant that on occasion I hit the other end of when it is bad to water xeric plants, with for most of us would be during cold winters, but a number of my plants I really have to be careful with in terms of watering them in the middle of summer, when we tend to hit a significant period where night time lows are >85F. Significant numbers of especially potted Aloes do not like to be watered then. They do not like the high night time lows period, but sitting in a wet pot seems to make it worse.
But back to my general watering approach. In the hot period, generally starting early/mid May, I water all my plants in pots and in the ground once a week. I usually keep that up through the summer until early-mid October, or when day time highs start dropping below mid 90s consistently. Despite my efforts to keep my plants to a universal watering scheme, there are a few plants I try to water twice a week throughout the really hot summer period day time highs >105, which are the Desert Roses, which really are more tropical than xeric in their water needs when it is hot.
If we have an active monsoon season (which usually starts some time in mid July and lasts through August into September) and we get frequent rains storms I tend to adjust my watering scheme to that, so reducing the frequency if we get good rain (if it rains in that period it usually a torrential downpour).
The rest of the year I look at the balance between night time lows and day time highs, if night time Ts are >55 and day time highs still get >85 I water once every two weeks, once things get cooler, I will go to once a month and when Ts get below 45 at night I stop watering completely. In good years we get winter rains and in December to mid February, I protect most of my small potted plants from that because the rains tend to be associated with extended periods of cold night time Ts, which is a bad combo especially for the smaller younger plants.
My soil mix is a pumice / cactus soil mixture in the range of 30/70, 50/50, and in some cases 70/30, though the latter I rarely use anymore as it dries out too fast in summer. I generally have plastic pots for plants I am growing in my shade structure and a combination of ceramic/clay/plastic pots for the plants I have out in the spaces we use (back patio, front porch).
For my in the ground plants I do not really do anything different though for a while I tried with using a soaker hose which I would string out around and between plants and then let run for a couple of hours. The idea would be that for in the ground plants a prolonged deep soak is more beneficial than a short heavy deluge of water from the watering hose which in the hot periods tends to mostly run off and evaporate. Having those soaker hoses out in the elements - especially the harsh UV we get here - means they do not last that long add the spiky nature of most plants and you'd really would like to keep them in place - ie. bury them. At the old place which we rented I did not feel it was worth the effort. In the new house, I think I eventually will, it is a compromise between putting a full irrigation system in and watering by water hose, it is just going to requite some planning and also to get to a point where I feel all the major plants are in place and established (which is not yet the case as at least one shade tree and a number of other plants are still on the list to be put in the ground).
