Winter time is here.

[marc206]

Ok last night was a cold 26F out of nowhere. This morning after dropping my son off at school, I looked at my trees a lot had frost on the leaves and soil was rock hard.
Last night I looked up what others were doing to protect their trees from frost. I read that most people start to winterize when it gets around 15F. Last year I only had a minor collection and we had a pretty warm winter. But this year I think it will be cooler and my collection has tripled since last year. Should I protect my trees from frost?

 

[Poink88]

What trees do you have?

 

[marc206]

Cotoneaster, Elm, hemlock, dougs, azaleas, cedar, pines, rosemary, apple, heavenly bamboo, dogwood, junipers, holly, JMs, boxwood, hawthorn and ninebark. With many different amounts and varieties of each.

 

[Poink88]

The list should help you get better response.

I am in zone 8b and I see you are 7b. You can check hardiness online of each of your tree but remember to factor that they are in pots. I've read that you should lower their hardiness by up to 2 zones due to this.

Good luck!

 

[cmeg1]

15 seems pretty extreme.I think that is the temp for intra-cellular root damage.

 

[cmeg1]

As for experience I once buried a pot wrapped in semipermeable landscape fabric(The gray and black kind without holes) on mounded earth so it didn't sit in frozen soil like a puddle of water. It was under an inch of Earth and mulch. The landscape fabric kept Moisture consistent as long as I watered the mulch a bit. The bonsai pot soil never got waterlogged because the fabric did not let much water into the pot. It was perfect moisture consistency in spring when I un- earthed it. I would overwinter in the ground or in a shed if I was you rather than leaving them exposed. It is just a hunch though, I've never used those wintering options.

 

[Dav4]

15 seems pretty extreme.I think that is the temp for intra-cellular root damage.

This varies from species to species...and this reference is for the actual root temperature, not ambient temps outside.

To the OP, what zone are you in? Winter temps that briefly fall into the low 20's or upper teens are unlikely to cause cold damage to hardy trees. The problem comes when temps are falling into the teens or lower every night and only getting up into the low 30's. If you are in zone 6 or colder, I'd definitely recommend winter protection for your trees- mulch the pots on the ground out of wind and sun...zone 7 or higher, maybe not. Fwiw, my temps fell to 23 F 2 mornings in a row last week...but daytime temps bounced back into the 40s...they're all still on the benches and will stay there for most of the winter unless we get an arctic blast that will last for more then a day or two.

 

[marc206]

This varies from species to species...and this reference is for the actual root temperature, not ambient temps outside.

To the OP, what zone are you in? Winter temps that briefly fall into the low 20's or upper teens are unlikely to cause cold damage to hardy trees. The problem comes when temps are falling into the teens or lower every night and only getting up into the low 30's. If you are in zone 6 or colder, I'd definitely recommend winter protection for your trees- mulch the pots on the ground out of wind and sun...zone 7 or higher, maybe not. Fwiw, my temps fell to 23 F 2 mornings in a row last week...but daytime temps bounced back into the 40s...they're all still on the benches and will stay there for most of the winter unless we get an arctic blast that will last for more then a day or two.

I am in zone 8b. All of my trees were fine outside last year but I only had 20-30 of them. Now I have hundreds and now I have more to lose.

 

[Dav4]

I am in zone 8b. All of my trees were fine outside last year but I only had 20-30 of them. Now I have hundreds and now I have more to lose.

I think most of your trees(don't know about heavenly bamboo) will be fine with little or no protection. By little protection, I mean placing them on the ground when cold temps are forecast for a day or two, maybe a week if the cold sticks around. If you know someone in your area that has a descent bonsai collection, you could ask them what they do, but zone 8b Seattle sounds pretty mild cold wise.

 

[Poink88]

I am in zone 8b. All of my trees were fine outside last year but I only had 20-30 of them. Now I have hundreds and now I have more to lose.

Wow, your area is much milder than I thought.

I have most of the ones you listed and I do not protect them here (zone 8b also)...BUT I doubt our lows are comparable.