If not at planting out then the next time it gets much below 20F. While there are a very few Washingtonias of some size still around as a rule these do not persist here. Plantings consisting of both Washingtonias and Trachycarpus tend to end up all Trachycarpus over time.

I do not recall any problems with transplanting them from my days working in a garden center in Phoenix AZ but am surprised you'd be planting one here......

Hi,
Thanks for the feedbacks. I saw them at Lowes with a label saying it's hardy to 10 degrees so I am hoping that they would survive:-)
Winsor

A Washingtonia should not lose any leaves upon planting out in a normal situation. W. robusta is most definitely not hardy to 10F degrees, and is not hardy long term in the PNW, so unless you treat it as a container plant and bring it under shelter when temps drop much below 28F, I'd think of it as an annual or experimental plant. They are very easy to grow as a longer term container plant if they are given a hot sunny spot and some protection from cold and wet in winter. They can take some degree of cold and even snow in winter where they get hot summers, such as the foothills of the Sierra Nevada Mountains, where they can be seen as quite old and happy specimens at up to about 3000 foot elevations, which do get periodic snow in winter and lows down to low 20'sF, but not every winter or for days on end.

I've been amazed by a Washingtonia planted against a south-facing wall in Dockton, WA on Vashon Island. It can look pretty bad in the winter but so far has bounced back and thrives in the summer. It's about 8 feet tall currently.

That's interesting to know about and sounds like a great use of a very protected microclimate. Washingtonia robusta can endure temperatures down to 10F (not without damage) in the New Mexico desert. There is a mature one in Truth or Consequences. But in our climate you can pretty much count on leaf loss around 25-28F and death in the 18 - 24F range.

As Bahia touched on at the end of his post low temperatures endured by plants for brief periods in hot climates are not as damaging as the same temperatures in northern regions. Up here the soil freezes, subjecting plants to the double whammy of cold foliage and frozen roots. The same Arctic Fronts that shove temperatures down into the teens and twenties (or lower) may persist for a couple weeks. In the south a 17 degree night may be followed two days later by a 71 degree day, with continued warmth.

Hot climates also do a better job of ripening and hardening off foliage growth than the cool, dull conditions that are frequent during the growing season here.

Hi,
Thank you very much for all useful info, I really appreciate it.
Winsor

Is it true that planting Washingtonia Robusta deeper than it's soil level (roots at ~10" deeper than soil) will protect it from freezing the roots in winter in the middle of South Carolina? Or should I replant it at soil level?