Over wintering bonsai lowest temps allowable

I have always heard a wide range of freezing temperatures that you should allow non tropical trees to be out in. We have very mild winters here in the part of Texas I live in. I have always been confused on how low I can leave them out. Every year I take all of my deciduous trees into the garage. After the first light freeze. It is usually 28-31 degrees. I wait for all the leaves to turn brown and move them in. I leave all of my conifers and semi deciduous trees out all winter unless the temps threaten sub 25 degrees. I then do a dance of moving them into the garage then moving them back out to the benches when it gets back up above freezing. You have to realize we can have one night of freezing temps then not have another for two weeks. I'm starting to think I might be babying them to much. I wanted to know what some of you in zone 7 do. Other zones input is welcomed. I have listed the different type of nontropical trees I have below to give you an idea.
Black pines
White pines
San Jose junipers
Shimpaku junipers
Chinese junipers.
Bald cypresses
Trident maples
Japanese maples.
Chinese elms
Korean hornbeams
Crape myrtles
Hollys

you should be good with just leaving them outside im not posive but the trident is the only zone 7 plant you have listed everything else can handle lower temps. depending on how much rain you get during the winter months would be your issue .you may need to keep them in a covered area and water them by hand to prevent waterlogging

Hi Jeremy,
Just south of you in zone 8b.. winter before last was a wicked one that put everything here into deep freeze (dropping to a low of 16F). From your list, I lost Crepe Myrtles and Yaupon Holly. Everything else did fine here outside. Not sure how this translates to your own yard (wind, exposure, etc), but that's my experience.

Where I live we have a 7a pushing for 6b kind-a climate. Temperature as a rule stops dropping roughly at -15C/5F.

Last winter brought us -20 degrees celcius (about -5F) in Feb. after a winter without any real frost, and many plants at that stage were already pushing their buds (Extremely early, due to weeks of 10C/15F temps). That is when a lot of people lost their trees: Due to unpredictable extremely low temps. Normal winters however, most people would be happy to leave their tridents, hornbeams, beeches, oaks etc outside all winter, as long as temps don't drop below the -15C/5F mark; These will however be in a sheltered area outside and/or with pots mulched / burried in the ground. Japanese maples are treated a little better.

Important to note: Many trees wont die of the temperature, but because of lack of moisture. When winds blow over your trees, they dry out fairly quickly. Keep them sheltered and when freesing stops, water them if needed.

Hi
I agree totally that many trees do not need baby care just because it is winter. The cold period is often just as important to the trees cycle as the warm seasons and, as mentioned already it is waterlogging that can cause far more problems than freezing.

white pines - essential to let them get cold,
black pines - protect roots at 0 C
junipers - def leave outside - trees are healthier for it
maples -acers - leave outside as overprotection makes the buds break too soon - protect spring growth from bad weather
tridents - depends on pot size - shallow root systems will need protection but I have let a big one freeze for the last 15 years with no problem
elms - mine do fine left out, others feel happier protecting
crepe & holly- protect
hormbeams - again - no harm will occur outside.

basically this winter my unheated glass greenhouse will have black pines, satsuki azalea, and a maple that i need in leaf early for a show. My large yew will have the pot protected from frost with an insulation board surround and the foliage of a hinoki will be protected so the colour stays nice for an early show.

cheers Marcus

I have at least one of every tree on your list. They survived up-and-down temperatures ranging from 8 degrees F to 70 degrees F last winter here in zone 7. All were unprotected on my tables.

Your biggest problem may/will be from cold dry winds; not freezing.