Watering in Summer

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I think the window for watering is 4am to 9am.  That gives the garden plenty of time for surface water to evaporate by evening so that the plants don't go into the night in a situation of high humidity.  With most plants and most foliar diseases, the critical factor that causes foliar diseases is not "free water" on the foliage.  The environmental factors are cool, moist nights and warm dry days (much as what we have here on the Central Coast!).

 

I've never seen any good studies that showed cool, moist soil in summer was better than hot, moist soil for root development.  But given that most Mediterranean climate plants do most of their root growth from late winter into spring and then essentially rest during the summer, it could be that those "temporary" water-temnperature situations in summerhave some effect on the roots.

 

With that said, there's a lot more to be said -- as others have already said.

 

First, a good "Mediterranean" garden should need little to no water in summer.  (Yes, I know, this has been a serious subject of another recent thread.)

 

Second, something I've found that works very well during the hottest part of summer when some plants are flagging and I know I shouldn't put water to the soil is to spray the plants or turn on the overheads.  Because it's so hot and/or windy, the plants dry out before evening.  This works for every Medit. plant I've used it on with no ill effects.  And no, water on leaves doesn't "burn" the plant (an old myth).  The real benefit is that I've not watered the soil and hence encouraged the complex of root rots (Phytophthora as well as Pythium, Rhizoctonia and more).

 

Third, the factors that lead to root rot are many and complicated.  It's not just that the soil is "moist and warm".  It also includes the fact that a saturated soil -- one that is wet from frequent waterings -- lacks oxygen and the root rot organisms thrive in such anaerobic conditions.  Most importantly, an anaerobic soil discourages (outright kills in most cases) the beneficial organisms of a soil, particularly mycorrhizal fungi -- the really good guys that are key in the survival and optimal growth of natives (in their native land). In the summertime, our mycorrhizal fungi go dormant and are not prepared for water, hence they themselves "rot".  Mycorrhizal fungi offer many benefits including that they actively keep detrimental fungi in check.

 

Another factor in root rot development is an accumulation of salt in the soil.  Much of California has hard water (it's INCREDIBLY HARD here and almost as hard in Southern California).  Most root rot organisms thrive on higher salt levels.  And, as a seque to my final point, salt levels in gardens have increased tremednously over the last couple of decades with the rising popularity of drip systems.

 

Fourth, drip systems (not that you asked, Pamela) are an efficient way to use water (as engineers would testify) but not close to being the most effective way to water plants to encourage them to become more drought tolerant in our climates.

 

Too many people have bought into the concept of Micro-Irrigation and there's too much money behind it so I don't suspect that it will be questioned too much nor too soon.  But there are many inherent problems with it. I won't go into the cosmetic issues nor a host of minor issues but the four big issues are that drip systems don't water in a way that encourages a plant to have a wide and deep root system, drip systems leave a soil saturated for too long,  drip systems concentrate salts and, fourth, drip systems don't push oxygen into a soil as do typical sprinkler and other, more "effective" systems.

 

Micro-irrigation -- including "drip" -- was invented in Israel to make use of little available water that offered a low-pressure situation.  It was created for row crops and some fruit trees.  It was not designed for a drought-tolerant landscape.

 

Joe