A question from the free-thinking gardening rebel.

Decades ago when I was learning how to garden it was standard practice to dig a hole twice the width and depth of the container and mix compost 50/50 with the native soil. When I was about to graduate, I was in a senior seminar class where a student pointed out that in Basic Soils we learned that "layers are bad for drainage" and suggested that it might be better to loosen soil twice as wide as the container and only as deep without mixing in compost. Since then this has become standard practice.

Along those lines I'm questioning our irrigation practices. Conventional wisdom here in CA is to water thoroughly but infrequently in the summer and reduce irrigation in the winter when it rains. Considering that 'Mediterranean climate' plants are adapted to warm DRY summers and cool WET winters, wouldn't it be better to water the other way; i.e. thorough deep watering between rain events in the winter and significantly reduced irrigation during the summer. These plants tend to be semi-dormant in the summer and susceptible to Phytophthora crown and root rots when watered in the summer.

Let me know your thoughts.

In an ideal situation you wouldn't need to water your garden at all. But ofcourse that depends on the types of plants that you grow (naturally occurring or in a similar environment)

And I'm not sure if 'mediterranean climate' is equal to warm dry summers AND wet winters (cool and dry perhaps, but not wet)

Assuming the plants in question are Mediterranean climate plants (ie. their habitat has a winter rainfall, summer drought climate) they should do very well with little or no summer water, provided temps don't get painfully hot in the summer. This would be Aeonium, Dudleya, a variety of plants from the west coast of South Africa, etc.

However, plants from other climates (eg. summer rainfall or tropical) may require some summer water to do well, depending very much on the plant and the situation. In all fairness xeric plants can often take a lot of summer drought if they are allowed to become established first. Your run of the mill agave or aloe will often deal very well with drought during any season, regardless of its climate of origin. I planted about 15 aloes and stopped watering after a year, and all of them survived our driest year on record, including an 8 month summer drought, regardless of whether they came from a winter rainfall climate.

There is definitely no reason to water more often or more deeply during winter, given that's when we get our rain. The average rainstorm here (not just a shower) will saturate the soil deeper and more evenly than it ever is when I water. Sure, if there's an extended period without rain, you might want to provide some water to keep plants looking good. But that's more like supplement to nature's goodness than a (poor) replacement for it (which summer irrigation would be in our climate).

One side note related to SoCal and NW BC local weather: we get some of our warmest and most of our driest days during winter (for example this past January we reached a couple degrees short of our annual high) due to the Santa Ana wind reversal events that take place at that time. (High) temperature and (low) humidity are big drivers for evaporation and transpiration, especially combined with wind. After 2 or 3 days with these conditions, the soil is very dry and plants tend to be beat up. The succulents look visibly deflated. So actually deep watering during winter makes a lot of sense if it occurs shortly after a Santa Ana event, especially when it hasn't rained for a while.

Since 80% of plants in retail nurseries (even here) are from more "typical" climates like England, continental Europe, Japan and southern China, they must be irrigated or die, at least here. For more xeriscaped landscapes, at least institutional and commercial, irrigation is standard practice. Many systems are on an ET (evapo-transpiration) schedule modification program. This automatically changes the watering duration depending on weather factors - warmer/dryer = longer cycle (more water).
Yes, a Mediterranean climate receives 90+% of it's rainfall in their cool winters, therefore, wet not dry. Or at least as wet as it gets.
This comes from a more 'landscape maintenance' point of view than a 'gardening' point of view, but the watering practices are essentially the same. I know it seems sort of counter-intuitive to cut back on water when it gets warmer and drier. But, if that's what the plants genetically "expect" then why not give it to them?

The way I understand it now is it all depends on the heat/temperature around the plant. Like California with its varying microclimates..
It may be summer weather near San Francisco but they have much cooler temps than my side. So in that area they can practice longer intervals in watering even in summer, and many succulents enjoy the cooler weather too. On my side since we get into a more intense and drier condition, then I have to step up watering a bit more. But still taking note that at 90F and higher and extreme heat, the succulents will shut down and wait it out. That is the time some gardeners do end up rotting the plant..since by then plant has gone dormant. So I have to consider moving the plants in shade otherwise whatever I do..they will just end up dry roasted. Very, very few succulents can tolerate excessive heat, so got to help them rest in shade or dappled light till they bounce back again in Fall's cooler weather.

As to winter time..Mother Nature's rain here in Cali is to all extent very intermittent and not in any way like the torrential downpours I have experienced living in the tropics. Provided media has been made very porous and temps do not go below 20F then cold survival for succulents is quite good. I like it when winter comes..finally much needed rain is here. But that being said, knowing which succulents with a higher threshold for cold temps is impt. Otherwise 50F is my bottomline, if it goes lower than that, I have to start moving some succulents indoors.

When I was new to succulents, I cannot understand how I killed many..then I realized the temperature is different each season. Overall Cali does have mediterranean climate..but intensity of heat varies, humidity levels vary. So got to take note of that and adjust accordingly. Especially now..season to season, year after year..growing conditions are so different. Got to protect the plants now from excessive heat...duration of heat waves is getting longer. Most succulents are drought tolerant..but got to take note many are not excessive heat tolerant.

That is also why in winter when frost advisories are announced, got to protect the succulents. A one hour exposure to excessively cold temps is bad enough..if it happens to rain too..then it is survival of the fittest mode for most of them.

CalPolygardener said:This comes from a more 'landscape maintenance' point of view than a 'gardening' point of view, but the watering practices are essentially the same. I know it seems sort of counter-intuitive to cut back on water when it gets warmer and drier. But, if that's what the plants genetically "expect" then why not give it to them?

The only thing the plants genetically "expect" relates to the conditions they came from in habitat, the natural cradle that gave rise to the species, the conditions that promoted its survival and evolution. For example, Mediterranean climate plants "expect" a summer drought. There is a fundamental difference (at least in my mind) between what a plant is programmed to survive based on genetics, and the way it may change its behavior or growth depending on local environmental conditions where it ends up growing. Nature vs. nurture, as it were. One does not necessarily override the other. Does that make sense? Cutting back on water when it's warmer and drier during summer may make sense for drought tolerant plants from a Mediterranean (winter rainfall/summer drought) climate. It does not make sense for plants from summer rainfall climates, except insofar as they may be more drought tolerant overall.

CalPolygardener said:Yes, a Mediterranean climate receives 90+% of it's rainfall in their cool winters, therefore, wet not dry. Or at least as wet as it gets.

That is an overestimate. In your climate (Pomona, or am I mistaken?) 80% of the rain falls from Dec-Mar, which includes an extra month outside of winter itself. This figure for other Med climate cities: Cape Town (months switched for southern hemisphere): 62%; Lisbon 47%. So even though it may feel like nearly all the rain comes in winter, that's not actually the case for any of these locations.

Baja, that's sort of what I'm getting at. That if plants from a Mediterranean climate are adapted to a warm/hot dry summer and a cool wet winter they should be watered more in the winter and spring wet season and less in the summer, which is contrary to the typical recommendation. Like I said in the beginning, the typical recommendation (even from the Native Plant Society) is to stop watering when it starts raining and start again when it stops raining. That sounds backwards to me. I would turn every winter into an El Nino winter and water very minimally in the summer.

Plants from other climates would obviously need summer watering. Even some of those will survive on less watering than they typically receive.