"Mediterranean" and Other Tree's Winter Hardiness

[hemmy]

Everyone was very helpful on my "too early <20F freak-out". All the trees all went into the garage that stayed at 51F and are now back out for nights forecasted at 33 - 63F over the next 10 days. Hopefully they'll start acquiring some winter hardiness and we ease into the colder temps. Also hoping that highs in the upper 80s highs this weekend don't mess things up (friggin Midwest!).

But I'm looking for some guidance on winter hardiness for my soft, former SoCal trees as they experience their 1st winter. I think the pines (Japanese black and red), junipers, tridents, osage oranges, apples, zelkova, gingko, and english oak can take a frost and then go into the cold frame. But what about more "Mediterrranean" climate trees? The attached garage is south facing on the SE corner of the house and has surrounding it on 2-3/4 sides. I guessing that it will stay above 40F and probably hit 70sF on those occasional warm winter days. It will have LED lights for the plants.

Here's my garage list. Any bad ideas? Thoughts? My biggest question is how to treat my Cedar Elm, twisted pomegranates, satsuki azaleas, and shohin Chinese Elms. All of which I'd like to bring into the garage after leaf drop (except the Azalea, which I'd leave out for light frosts and then bring into the garage under light. I'd like to bring in my shohin Japanese maple and apple, but I think they need the extra cold under 50F. My maple did great in SoCal with temps rarely below 45F.

Pomegranate (Punica granatum 'Twisted Trunk') - I see Zone 8 in the ground, so Zone 9 in the pot, 20F. I figured I'd let set in the open cold frame down to high 20s, but mulched in so the pot stays above freezing. They are both too tall for the cold frame, so I was hoping to keep it in the garage once it starts getting really cold.

Satsuki Azaleas, USDA Zone 7, 0ºF (Zone 8, 10ºF), leave out for light frosts and then bring into lights in the garage.

Cork Oak, Quercus suber, Zone 8, 10ºF (so in a pot Zone 9, 20ºF), Habitat range includes coastal Algeria, Algiers, Tangiers, where average winter low is 42-47ºF. I was going to keep this under raised up LED lights in garage.

Coast Live Oak, Quercus agrifolia, some sources Zone 7b & others Zone 8, 10ºF (so in a pot Zone 9, 20ºF). Same as the corks, under light in the garage.

Valley oak, Quercus lobata, deciduous, USDA Zone 7, 0ºF (in a pot Zone 8, 10ºF), warm range down to San Diego where winter avg. 49-50ºF. No or minimal light in garage.

Blue Oak, Quercus douglasii, deciduous, some sources Zones 5-10 but others Zone 8, 10ºF (so going in a pot, Zone 9, 20ºF). Going to let it frost and then go into no or low light in the garage.

Floss Silk Tree, Ceiba speciosa, Zone 9, 20ºF (in a pot Zone 10, 30ºF). It was deciduous outside in SoCal. LED lights in the garage.

Coast Redwood, Sequoia sempervirens, USDA Zone 7, 0ºF (Zone 8, 10ºF), LED lights in the garage.

Sago Palm, Zone 8, 10ºF (pot Zone 9, 20ºF), garage or house under light

Zamia sp.?, palm, Zone 10b, 35 °F (pot Zone 11, 40 °F), garage or house under light

Black Bamboo, Phyllostachys nigra, USDA Zone 7, 0ºF (Zone 8, 10ºF), garage under light

Olives, Olea europaea, - I was going to treat olives like tropicals, indoors or in the "tropical" heated section of garage.

Bougainvillea, treating like a tropical heated garage under light

Goumi Berry, Eleagnus multiflora, Zone 5, cold frame with other trees. It doesn't seem very winter hardy, but several sources claim otherwise.

Thanks in advance!

 

[Dav4]

I can't speak for all your species listed, but I can tell you most Mediterrenean species can take light frosts but should be protected from hard freezes. This is how I've treated my own European olive over the last few winters. Any risk of falling near 32 F and it's going into the garage or in the house. Since moving to MI, I now treat it almost like a house plant. Last winter, I tried to give it a more prolonged dormancy by keeping it in the 30's in my garage... it didn't do well so now it's indoors and under lights this year.

I think the pomegranate is ok with light freezes but still needs significant protection from severe cold.
Your goumi can freeze solid in the cold frame for sure.
The Japanese(?) red pine is generally more cold hardy than JBP and won't need much protection in your zone... mulch the pot out of wind and sun is about it. The maples would be fine outside with protection, too... watch the vermin! The cedar elm can freeze but will need extra protection from severe cold I think.

 

[BrianBay9]

I faced this problem when I moved to the midwest a decade ago. The cold hardy trees are fine. The tropical/subtropical trees do well indoors. Even the deciduous "Mediterranean" trees were OK to store without light. It's the evergreen, "in between" trees that become a nightmare to overwinter in the midwest. Perhaps some locals have it figured out, but I gave up on cork oak, coast live oak and coastal redwood. Olives do OK inside under lights.

 

[hemmy]

It's the evergreen, "in between" trees that become a nightmare to overwinter in the midwest. Perhaps some locals have it figured out, but I gave up on cork oak, coast live oak and coastal redwood. Olives do OK inside under lights.

I’m changing my like to “dislike”!

I bought a nice cork oak before we left, because I loved working on the species at the Huntington.

What do you think the issue was for those evergreen oaks and redwood? Too little light, too hot/cold, humidity levels?

The cork and my redwood are probably my nicest trees. I even don’t mind the full time job that is pinching the redwood during active growth.

 

[BrianBay9]

What do you think the issue was for those evergreen oaks and redwood? Too little light, too hot/cold, humidity levels?

I think the problem I had was giving them enough light, enough (but not too much) cold, and probably was too dry in the house. My lights and grow tent were set up for my tropicals, so they didn't particularly like that either.

I'm sure with enough work and a segregated space you could keep them happy enough inside through the winter, but that was more work/expense than I could give them.

 

[Dav4]

I think the key to keeping those questionable evergreens is finding a place where they will reliably stay below 40 F for most of winter and early spring but not get exposed to temps significantly below freezing. I think they all can experience sub freezing temps without damage but deeper freezes will be problematic.

Full disclosure... that's what I did with my olive last winter... weakened it badly but it recovered nicely this summer. I suspect the coastal redwood and other zone 7 trees would be fine in that scenario, though.

 

[hemmy]

I think the key to keeping those questionable evergreens is finding a place where they will reliably stay below 40 F for most of winter and early spring but not get exposed to temps significantly below freezing. I think they all can experience sub freezing temps without damage but deeper freezes will be problematic.

Full disclosure... that's what I did with my olive last winter... weakened it badly but it recovered nicely this summer. I suspect the coastal redwood and other zone 7 trees would be fine in that scenario, though.

Thank you. I think the cold frames will likely get too cold of air temps for some of the broadleaf evergreens to retain leaves and fine branching. Fortunately, years of growing them in Ventura has gotten me comfortable they have gotten enough dormancy or rest period with overnight temps from 40-50F and days in the 50s-70F. The garage was already in the low 50s with outside temps in the 20s. As Brian mentioned above, I think light, humidity, and airflow at the optimal levels will be the challenge. I'm also concerned with keeping the garage cool when the daytime temps increase. I'm wishing we kept the portable AC unit, I could run it in the garage and vent the heat to the tropicals! I think ultimately the answer will be less trees next year.

 

[Crazy Diamond]

Olives dont mind the cold they like cool winters, what they dont like is being wet all the time

 

[hemmy]

It's the evergreen, "in between" trees that become a nightmare to overwinter in the midwest. Perhaps some locals have it figured out, but I gave up on cork oak, coast live oak and coastal redwood.

And we’ve entered the ‘nightmare’ phase. The live oaks, redwood, and a recently wired JBP stayed above freezing in the garage under lights during the -6F snap. But now we have 6 days at or above freezing. I’m debating taking the bigger cork oak outside and setting it in the mulch inside the open cold frame in full shade. The roots would stay above freezing.

But would too the drastic change in light intensity be detrimental? Considering that they have to come back inside when the temps go back down in a week.

 

[BrianBay9]

You're asking the wrong guy. I never figured it out. Maybe some local club members keep these kinds of trees and can advise on their success?

 

[Dav4]

We're not going to see sub freezing temps here for at least another week if not longer. I went out of my way to keep temperatures in my cold room in the upper 20's F over the last week or so, but the ambient temp in there is 36 F and only going to move higher. A few days over 40 will be fine but if cold weather doesn't come back soon, I may be moving everything outside for a short vacation, as I suspect some of the trees have already met their chilling requirements for the year and true spring is a long, long, long way off. This is the ONLY reason I don't like mid winter warm ups . Also, I wouldn't worry about light intensity as the sun is as far south as it can be during the calendar year. When I pull my JBP from the cold room this coming spring- read that as April most likely, when the sun intensity is significantly stronger, they go right on the bench with no issues.

 

[Deep Sea Diver]

Well… likely not. It is definately possible to get light damage, depending on the species if one were to just jerk a tree outside after being in weak artificial lights for a look period of time. Mostly for soft tissue leafed out trees though, say an azalea.

Folks do a process called ‘hardening off’ for both light and temperature over a week or two to acclimate plants kept inside to get used to outside conditions. ….Out for increasing amounts of day time over the hardening off period

About the high day light temperatures….scrolling back in time. Dormancy requirements are fulfilled by gathering the accumulated chill hours, vs a continuous number of chill hours.

Once each species of tree gets the amount of accumulated chill hours needed is when issues can occur. btw: Varying genetics within a species are a factor too.

At this point, a higher temperature trigger can trump the photoperiod trigger, and deaccilimation can occur… taking from a minimum of about 3 continuous days above the individual species deaccilimation temperature to about 7 days, species dependent.

Fluctuations are not usually an issue as long late afternoon through nighttime temperatures are in the zone.
For example I wouldn’t go to General Quarters for fluctuations that looks like the past week data in this image for Greenhouse Two.



Now if nighttime temperatures were consistently above say, about 42F / 5.5C…. then I would start to be concerned. In this case the nighttime temperatures will be in about 40F/4.4C for a day more, then move closer to the 32F/0C range as the week progresses.

Given your scenario, wouldn’t just opening the garage door during the day help you during warmer days?

cheers
DSD sends

 

[Ben in Kzoo]

Having to leave for a trip soon, I am glad I found this thread… but I didn’t get a definite answer.
For my olives in particular, I am wondering if they would do well over the winter in a shed I keep between 34 and 36 (it’s not well insulated, some trees have light frosts)
The shed has no light in there (my pines and azaleas are there anyways)
Recommendations: put the olives in the shed, or keep under lights indoors around 70 degrees?

 

[hemmy]

Having to leave for a trip soon, I am glad I found this thread… but I didn’t get a definite answer.
For my olives in particular, I am wondering if they would do well over the winter in a shed I keep between 34 and 36 (it’s not well insulated, some trees have light frosts)
The shed has no light in there (my pines and azaleas are there anyways)
Recommendations: put the olives in the shed, or keep under lights indoors around 70 degrees?

Sorry, this is my first olive winter. Mine are inside house and also heated grow tent in garage under light. I’ve read olives in the ground need above 15-20F. But in a pot, I would not let mine freeze (especially the roots).

For yours, I think it would depend on how long you are gone, the risk of below freezing in the shed, and if they will get proper watering inside under the lights. I’d hesitate to go from 70F to 34F. I also wouldn’t want them in complete dark for more than a week. But maybe if it is below 40F, they wouldn’t need light or water.

 

[hemmy]

I had read that fruiting olives need 2 months or 300 chill hours of dormancy to fruit. Optimal winter temps 40-50F (which was also my SoCal night temp range). I’m not looking to make olive oil, but I will try to reach those conditions. Since mine probably can’t go out until late April to early May, I will wait until mid-Feb before they go into the garage under light. After a couple months of winter, I’m more comfortable with temp. expectations and management for my ‘Mediterranean’ section in the garage. Which is 40F-60F.

 

[Nivel]

Olives can handle 32 F or 0º C with no problem, just avoid frozen soil or cold wind under 32F. You can place them outside under cover to protect them against frozen dew and they will be ok.

 

[Knightlife]

I even had a friend who kept their olive tree in a dark cold cellar… eventually it dropped some leaves but then recovered in in spring. Olives are very tough.

 

[Nivel]

Crazy week in January 2021 and today. Oh I remember now I wrapped the pot and soil with newspaper .

 

[Ben in Kzoo]

I am thinking more and more that olives need dormancy too, and preferably with light
I think I’ll move them in the garage after I get back, and next year have them in shed with all the rest
Thanks all

 

[hemmy]

Well the young cork and live oaks are waking up. But the bigger cork doesn’t appear to have any swelling buds. I will try and repot the small ones this week. They are all in the garage under LED or Fluorescent. Outdoor temps are warming up this week so I expect the garage is going to be 65F day, 40sF night. Any advice on cork oak repots in the climates? Bottom heat?