Is there a temperature below which you would not irrigate?

[Foggy Paul]

Here in SF we had a good drenching storm in mid-November, about three inches of rain, but since then nothing, and nothing is on the horizon for probably another two weeks. It's been clear and cold, about 52°F / 11°C during the day and 43°F / 6°C at night. I am guessing that the soil remains damp under our thick mulch. But I also have read many times that people water their palms year-round if rain is insufficient, especially for thirsty species like Archontophoenix, Hedyscepe, Rhopalostylis and Geonoma undata, all of which we have. Is there any potential harm in irrigating with these temperatures? Admins, please feel free to move this to the Climate section if that is more appropriate. TIA.

[tim_brissy_13]

Think it’s a h good question for the main forum rather than climate. My short answer would be yes, there’s definitely a temperate below which I just would water. The long answer would be I think it’s species dependent and also on a variety of other factors; soil type, natural rainfall, whether it has been windy etc etc. The temperatures you’re getting now are similar to what I’d get in winter during a chilly spell and I’m reluctant to water anything at those times. That being said, all the species you’ve mentioned are difficult to overwater. I still probably wouldn’t bother unless you’re getting weeks in a row without rain at those temps. Could you dig down to see how the soil feels below the surface?

[Foggy Paul]

Thanks @tim_brissy_13. It has in fact been weeks in a row with no rain. I can’t easily dig because we have gopher mesh underneath the entire yard, but every time I’ve planted anything, the soil has always been moist as it is cool here year round. Personally I’m inclined not to irrigate, but I keep reading that especially with the king, too much water is never enough 😆

[PlantMorePalms]

CIMIS publishes historical and real time evapo-transpiration data for California. There's no station in SF but there is one in Pescadero (probably most similar to the Sunset) and one in Oakland. I did a lot of research on irrigation when I set up my system and base my schedule on this historical data, though you could also use the real-time data if you wanted to. There isn't a lot of academic research done on irrigation needs for ornamental palms, but I use a plant factor of 0.75 since most of the palms I grow are pretty thirsty. So, if you look at the table below, reference evapo-transpiration in an average December is 1.4", so a palm would use say 75% of that, or 1.1" of water in a month, or 0.26" per week. I irrigate after ever 0.5" of cumulative evapo-transpiration to keep the soil pretty evenly moist, so in the middle of winter if there's no rain every other week should suffice. 

https://cimis.water.ca.gov/Stations.aspx

 

A much easier and more approximate approach is to simply take a long iron dowel rod and push it down into your soil, if it goes about 12" deep without much force, the soil is adequately moist, if it goes less you likely need to irrigate. 

[Foggy Paul]

That is extremely helpful. Thanks @PlantMorePalms. My sister has a vacation house in Pescadero and I spend considerable time there, so I am very familiar with the climate.

[PlantMorePalms]

Looking at the data for the last several days, even with the cold weather we've been having, daily evapo-transpiration is running at 0.04" per day, so that would still get to 0.5" in about 16 days.

[happypalms]

That depends on the forecast day temperatures and how full the moon is, for winter watering if a risk of frost try to avoid container waterings, try to pick a higher than average day temperatures to water your plants. Palms dislike cool feet in winter and the same us humans. If a full moon is approaching then you will get colder temperatures around that time along with the risk of frost. 
I try not to water in winter as much as possible, letting the rains do that job for the ground and containers. Maybe twice throughout winter I may water my containers, with temperature lows as 2 degrees celsius I try to avoid watering, if you do have to water in winter do it around 9 or 10 o’clock do it has time to dry out a little before the cool night air. So temperatures below 10 degrees Celsius I avoid watering. 

[TropicsEnjoyer]

50-60 degree day today, I don’t really water during winter but I can’t stop the rain right now…

[Jim in Los Altos]

Paul, It’s been warmer down here and I haven’t watered since the November rains. The ground is still very moist as relative humidity levels have remained high. Looks like the weather will remain pretty much the same for another two weeks before rains return so I’ll probably hand water a few plants that are in the sunniest warmest parts of my yard in a few days. With your chillier temps, I’d guess your soil is still holding a lot of moisture. 
 

 

 

[idontknowhatnametuse]

I don't water below 15°C. And if I do, it's with warm water.

[BayAndroid]

I'll simply say that I am experiencing very similar conditions in my location (Bay Area) and I chose to water. I figure if we were having normal rains, the ground saturated, it typically doesn't matter that much. I actually noticed some possible sun damage on some younger palms that I had not seen during the summer. The difference of course, could be my well draining soil. I don't have much, if any mulch right now, so those are all factors. I think you'll be ok either way. 

[Harry’s Palms]

We haven’t reached the cold down here , it is cooler than it was but still warm enough to water regularly., It seems , up in the Bay area , you guys are quite a bit cooler right now . Another warm spell is predicted this week so more water because we are not getting any rain since the November deluge. At my place , it has not yet dipped below 52f in the early hours with daytime temps in the upper 60’s to low 70’s. It looks like we will be warmer this week . Harry

[Darold Petty]

Paul,  I have irrigated 12 months per year for many years, sometimes for dryness, and sometimes as a political statement.  I would urge all California growers to read a book called "Cadillac Desert".

[sonoranfans]

Irrigation would depend on a number of things like

1) what palm species, wet lover or a deep rooted drought tolerant species.

2) soil type, does it retain water well or is it just sand are the extremes.  I have some extremes in my yard where I have high sand and high clay/organics.

3) weather: is there much dew? or is it the desert?

4) is the palm root system established or is it a new planting?

 

I have grown palms in arizona in heavy clay and in florida in sandy soil, as much as 3/4 sand to 3' deep.  

We rarely see freezing here but we have hit 39F 2x, in the 40's 5-8 times so far.  No rain for a month till last night.  I have not changed my irrigation timer from summer (3x a week) but I have stopped supplemental watering using hose or rainbird.   We have had a lot of dry breezes this winter so I watch the wet loving palms to see if they look thirsty.

Some palms really dont like consistently wet roots.  These are the ones that I sometimes cut the irrigation off for when it rains in summer.   I also separate the wet lovers from the drought resistant palms for easier care.   I have Bismarckia, (BxJ)xJ, and BxJ that are not targeted with the irrigation system for the reason of allowing better drying in relatively unammended sites.   Fresh plantings get increased water for at least 18-24 months depending on species.

The simple answer is I adjust the irrigation timer frequency with ambient weather(wet summer, dry "low" humidity spring and winds).  I never stop irrigating but I do cut it way back in volume(manual rainbird and hand watering).  

[Foggy Paul]

Wow, so many great replies here, thanks all! If @Darold Petty irrigates year round then I am inclined to do so as well 😁 @Harry’s Palms I grew up in Sherman Oaks and remember those lovely warm winter days in SoCal. Here we have fairly sandy, fast draining soil in most of the yard, and most of our palms are on the thirsty side. The only real drought tolerant one is Chamaerops. In addition to the species mentioned above, we have a few Chrysalidocarpus, Chamaedorea and dwarf Ravenea. Unfortunately all the yard is on the same drip loop so the only way to provide additional is by hand, except I have a dedicated hose sprinkler going to the area with the Hedy and Rhopie. I did give a lot of consideration to relative water needs when laying out/revising the drip, and plan a wholesale redo next spring as the palms have grown considerably since planting. I've been hand watering the king frequently but stopped all overhead watering last week. These comments have given me a good idea on how to proceed.

[Harry’s Palms]

@Foggy Paul Yes , the Indian Summers extend our growing season and are nice , as long as we don’t get the howling Santa Ana winds with it. The one negative of being up on hospital hill is exposure to the winds. Harry

[Josue Diaz]

I am in Fresno, but we're under that dreaded tule fog at the moment. Haven't seen the sun since that last rain in November just prior to Thanksgiving. Just fog all day long. My soil is still wet and my palms look good, so I probably won't be irrigating unless we go another month without rain and I notice the soil becomes too dry. 

[mnorell]

If you're in the Tule fog, your humidity and dewpoints are going to be at saturation, so why would you irrigate? Virtually all of your plants (including palms) are likely to have fully open stomata in these conditions and are surely gorging themselves on the atmospheric moisture in addition to what they can harvest from your soil moisture. And of course your soil-structure/composition is all important in figuring this out in your situation once your humidity and dewpoints decrease. I'm sure your Rhopies would be just fine with irrigation since it's plenty chilly and wet where they come from, but IMHO it would just be a waste of your $$$ to do it, particularly if they're established. 

I agree with what Tom Blank says above, and will add anecdotally that I lived on Big Pine Key in the hot, hot Florida Keys with very little rainfall for months at a time and brutal tropical sun bearing down, particularly in springtime with few clouds and near-zero rain. On a limestone rock, basically. And very different from Miami and much of mainland Florida, where there is land and convection to make rainfall, the Keys have nothing really to generate any rain on their own. And yet they are covered in vegetation. The Lower Keys have a freshwater lens that plants can tap into (it was about 3' deep at our house) if their roots can reach, but I had many plants--containerized, planted or native--that just survived almost entirely on the perpetually high humidity and the occasional bit of rainfall for all that time. And in the upper Keys (e.g., Islamorada and Key Largo) there isn't any groundwater, and yet plants survive there as well during the dry season. Many parts of the world have similar situations where there isn't much regular rainfall, and yet plants can do just fine using whatever atmospheric or soil-based resources are at hand, through drought and deluge.

I now find myself in the Palm Springs area, where it is much, much drier in winter than either Florida or the Central Valley of California where you are, and palms here are generally still growing albeit at a very slow pace, I reduce irrigation markedly for the cool season, but don't turn it off completely. I factor in, additional to simple observation and past experience, the individual needs/metabolism and stress-tolerances of the plant; soil composition/structure (our porous sand and DG/granitic alluvium); sun/shade exposure and positioning; our low atmospheric humidity, in which water transpires out so very quickly; and the level of establishment of the plants (in my garden usually about three years for most plants to establish a far-ranging root-system). I change cool-season distribution of irrigation to one-minute spurts late morning and very early afternoon where solar warmth is still incoming (and always water containerized plants about 10-11am for that reason)...I avoid any late-day irrigation, which will likely deliver quite an unhealthy, wet chill to the roots of any tropical lowland plants.

You'll of course have a very different situation where you are in Fresno, but this just to illustrate that I think all of the above factors have to be considered by anyone in delivering the right amount of irrigation, always keeping in mind the often very diverse native climes from which our garden plants originate.