100+ Temperatures by this Thursday?

Lamorinda:

Beginning Tuesday, and peaking on Thursday, we’re looking at some of the warmest temperatures thus far this year:

https://www.wunderground.com/forecast/us/ca/orinda/KCAORIND17

Considering our microclimates, and WeatherUnderground’s established track record of underestimating high temps, it’s realistic to expect we could see over 100 degrees by mid-afternoon this Thursday. Usually we ramp up to this kind of heat in July or August. However, since we’re faced with an extended “heat event” this early in the season:

*** Please consider deep-watering BEFORE the heat hits.***

There is a significant delay between watering and most plants’ ability to actually make full use the water, and spread it to the furthermost tips of the branches and leaves. Ideally, this would be done by Tuesday evening / Wednesday morning (Wednesday evening at the latest) in order to prepare for Thursday’s projected baking.

Those who only utilize drip irrigation should take this especially seriously; supplemental hand-watering will be necessary. Container plants (hello, terra-cotta pots!) will be particularly vulnerable to heat and the kind of late-afternoon winds we’re seeing increasingly often. But, as our water table is already dangerously low during this drought, watering plants that are in the ground — deeply and infrequently — is nearly always better than watering shallowly and frequently. This is why I like hand-watering and soaker hoses better than drip irrigation, or sprinklers.

For those who rely on sprinklers / overhead watering: please resist the temptation to turn such irrigation on during the warmest part of the day. It’s estimated that up to 40% of water is lost to evaporation when using sprinklers.

That said, on Thursday, when humidity drops and temps inch towards 100, it can be helpful to briefly “foliar water” our more sensitive flora — especially near the tips of the branches — during the warmest part of the day. This temporarily raises humidity and lessens the possibility of leaf scorch and wilt. I do this with my azaleas, camellias, bamboo and Japanese Maples, especially.

See you out there. Stay cool — and hydrate!

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