The toughest thing to factor would be any plant newly in the ground -- good roots or not.

If you had to select only one method (versus a combination) to keep your plants alive over winter: water, leaf-envelope, heat, roof including wind-control on one side, GH, humidity control, etc.
I'd choose roof (assuming it's not a Zone 11 plant).
Barb

Yep,I think in your area all you would need is a mini g/h type set up.In Iowa you may be able some years to go with this set up, if we are talking the most cold hardy of the cold hardy;sabals,trachycarpus,needle palms,etc but heat would need to be provided some years as we almost always(always as far as I know)go below zero F at some point.I think at some point with the right protection and hadening off you may be able to bring a sabal,needle or trachy through below zero weather but I have not personally tried this,although I hear it is not uncommon for them to survive this.

In the end, we can't eliminate the risk, just plan for it.

Arizona gardening websites warn against unexpected cold temps that occur at some time each winter.
And even Florida gets nailed now and then with frost.

Barb

Here is a pic I took of the west side of the yard at night,I used 8 strands of C-9 lights,I also put 4 lights a piece in the strofoam covers,this adds about 40F+ to the inside temp,I hope the mini g/h's are as warm as they are bright 8)
<a href=" " target="_blank"><img src=" " border="0" alt="Winter protection"></a>

Nicely done, Jim.
Be that'd work nicely for temps down to 10 F.
Or even a bit lower, I'd imagine.
Barb

I had it on for about an hour today,(not while sun was up )the outside temp was 20F and inside it was 50F,it does have some ice and snow on it and that does help to insulate it,however if I turn it on the ice/snow will melt and it will loose some insulation but it was only on for an hour and if I can get a 30F bump,I figure I'm good to -20F as these palms are acclimated at this point and have already seen 12F with NO damage.The nice thing about these x-mas lights is if they make it to warm inside,you can always loosen a few bulbs!

Thirty degrees above outside temps.
Great!
A good feeling knowing your valuable plants are safe for the entire winter.

You'll want a chair inside 😆
Barb

Funny you should mention a chair,I guess great minds think alike 😉 Here are some more pics of the rest of the mini g/h's and some inside pics of the larger g/h.I have not had much of a chance to use the chair in the past month but after this week I should be able to enjoy it more often!The pic with the thermometer is 4"down in the soil-
<a href=" " target="_blank"><img src=" " border="0" alt="Chill'in"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="Looking back"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="soil temp 12-6-08"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="Parryi 12-6-08"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="2 Trachys 2nd winter"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="W/P 12-5-08"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="12-05-08"></a>

Looks fantastic!
What do your neiboughrs say? 😆

Attaboy, Jim!
Those agaves are especially nice.

I looked for agaves last month...not one to be found around here.
Will check again in spring.

Since your goal is to increase hardiness in these planted specimens, I presume you'll nudge them closer to freezing than the current 47F soil temp.

What soil temp will you be trying to maintain as "real winter" arrives?

Barb

Ha,"real winter weather" has arrived here! Last winter the lowest soil temp was 40-41F under protective mulch,there is about 3" of (mulch)gravel in the cactus garden,so I don't imagine it would get much less than that .My plan now rather than taking these to single digits, is to not let it drop below upper teens as I don't think parryi or havardiana have seen much cold weather where they came from so I will baby them for 4-6 weeks. The Mazari is one I am really pulling for!
<a href=" " target="_blank"><img src=" " border="0" alt="Y.gloriosa"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="12-6-08"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="12-6-08"></a>
<a href=" " target="_blank"><img src=" " border="0" alt="Mazari,hanging in there"></a>

Jim,
Your hardier plants will certainly benefit from the parryi/havard.-protection temps.
Still growing!
They'll "think" there wasn't any winter at all! 🙂

The Mazari will only become more beautiful...already great color.
Barb

I would really like to see the Mazari make it,I have tried so many of these,as with most plants be tried in colder zones getting one that is a little older is the best bet,this palm is very well rooted and I think some of its color loss from earlier this season is from cold and miosture together.The Mazari was just starting to get going as the cooler fall weather hit,maybe a hot summer would do the trick.Barb,have you tried e-bay for agaves,etc?,this is where I buy basically all my plants.
<a href=" " target="_blank"><img src=" " border="0" alt="Nannhorrhops S.silver 7-17-08"></a><a href=" " target="_blank"><img src=" " border="0" alt="Mazari,hanging in there"></a>

Jim
D.Francko of Palms Won't Grow Here and Other Myths states that Mazari palms might be even more cold hardy than Needle palms, so that's encouraging for you.
AND they're reported to LIKE hot hot temps...up to 125 F.

I saw Agaves a couple of years ago (when I didn't want one).
Now that I do, they're all sold out.
Will try the nursery again in spring; they'll probably get a supply at that time.
I'll try eBay last...shipping into Canada from the US is such a pain, unless I find a Canadian supplier.

Good soil temp you've got.
Barb

I have read(palms won't grow here etc)that to,I have also heard that they usuallyy don't survive below middle teens but I think people sometimes are not aware that there is a big difference between a palm stressed in drought mode(so basically dry) going into cold weather and one that is wet,this is one plant I payed special attention to keeping dry.It is always tough the first year trying to keep things watered in and not having them be wet going into winter,this mazari is very well rooted and looks like it has a good chance! 8)