I'm sorry, the posting intended to ask about saving blue salvia over WINTER in Minnesota, not over night. I'm sorry about the confusion.

Mary Ann, I save both the Blue Angel type Salvia patens and the Black and Blue salvia through the winter successfully, at least for the last several years. I wait until frost takes the tops or they die back, whichever comes first and then dig them carefully to avoid breaking any of the fleshy root.

After digging them, I clip back the tops so that the stem is only 3-4". I used to put the roots carefully in dry peat moss in a plastic bag with the stem end up. Lately, I've been lazy and just put the roots in a paper bag, stem end up, and then put the paper bags inside a plastic bag, left open a bit at the top. I put all of this in a cold, dark place (my underinsulated entryway) and leave them there all winter. At the end of February or March or so, I'm usually surprise to see that they've started to sprout. I pot them and put them outside in an unheated greenhouse in April and cross my fingers, and most pots generally work for me.

BTW, you can tell which is which after digging them because the Salvia patens has smooth roots, but Black and Blue has constrictions regularly along the roots.

Thanks for reminding me to dig mine soon. Good luck!

Bitterwort, thank you so much for your response and a detailed instruction on how to save blue salvia. I will try to dig them up this weekend! I think for geraniums and this, my challengen is to find a place that's cool enough. My basement has heat, so not that cool, but I'll try to find a spot that's farthest away from the heat source. Garage will get freezing so probably too cold.

One question I have is how much dirt can left on the roots while they are in bags over winter. When I dug up geraniums last weekend, I pressed on the roots/dirt to get the dirt off, and I noticed that many small root bits fell along with dirt. Not sure if I'm not supposed to do that or it's OK to have dirt on the roots while they're in bags over winter.

Again, thank you so much!

I don't grow geraniums, so I don't know about those. With the salvia, I remove as much as I can without getting too crazy and damaging the roots. The salvia roots are fleshy, sort of like dahlia roots although not quite as thick. They seem a bit brittle, so I try not to stress them by breaking them up too much.

It doesn't matter at all if the smaller roots fall off--they will regrow from the fleshier roots next year. What you are trying to accomplish is to keep as much of the plant and its storage roots intact--it may look a bit like a bunch of very thin sweet potatoes joined at the top where the main stem comes up. If what you have looks remotely like that, you should be in good shape. As for storage, the goal is to keep them dormant (but definitely not frozen), so think cool, fairly dry, and dark. Good luck!

Hi, Bitterwort, thank you so much for your response!

I did try to dig up my blue salvia, and boy it was hard! It took a good hour or more to dig two of them up. They were in a maybe 1ft x 1ft x 1ft wooden container each, and I just could not pull them out. One of them, I realized had grown into the bottom of the container (put it in bag with the bottom still attached). The other wasn't, but I had to turn it up side down and pour the dirt and the plant out to get it out.

I realized that they did not have "fleshy" roots at all. The roots were all "thin" and wavy, like hair. Maybe I found one that was a little wider, but still loooked like a line. So maybe mine was different from the kinds you mentioned. They did look like the one in the photo in this link and seems like they're called "blue salvia" as well.
http://www.creekviewlandscape.com/per_blue_saliva_1.html

Anyway, they're in the basement in a paper bag inside a plastic bag now. I hope it does work, and I will report in spring how they fared!

Here is a link that might be useful: blue salvia photo

Oh-oh, Mary Ann--now that I see the photo, I realize that I have steered you in the wrong direction. When you mentioned the Black and Blue salvia, I mistakenly assumed you were referring to Salvia patens, what is often referred to as 'Blue Angel' and similar varieties (see link below). These and the Black and Blue (S. guarantica) do have fleshy roots that can be saved in the house over winter.

If yours really looks like the one in your photo, I can understand why you didn't find any fleshy roots. It is more likely to be Salvia nemorosa or something similar to that (a "meadow sage") and those are hardy here, at least in the ground. (See http://www.bluestoneperennials.com/SAEF.html) I have only overwintered those in the ground. My understanding is that a pot exposes plants to harsher conditions more like increasing the zone rating a couple of numbers, so your effort of digging them may not have been wasted. With fibrous roots, like your plants have, I don't think the strategy of keeping them in a bag will work well as it does for the fleshy roots I was talking about. You don't by any chance have a place in the ground that you could dig up quickly and water those plants in well (and repeatedly until the ground freezes hard for the winter) instead, do you? If you do, I would try that strategy instead.

I am very sorry I misunderstood what type of salvia you were talking about! It does sound like you had quite a fight with those roots, but they may have a better chance of overwintering out of the containers. There's a FAQ on this page about overwintering perennials in pots that seems to offer good advice.
http://www.bluestoneperennials.com/faq.html#winter

Good luck! I hope it works for you.

Here is a link that might be useful: Salvia patens 'Blue Angel'

I also would plant them in the ground and mulch them well right away. The mulch will help keep the ground from freezing for a bit extending the time for roots to get established.

Bitterwort, thank you for clarifications and further advice! mnwsgal, thank you for your advice too.

Today, I did put one of blue salvias in the ground. The soil in the area that I dug up looked clay-ish, so I wondered if it was soft enough for the roots to grow in but I also saw an earthworm squiggling about, so hopefully it was good enough. Next weekend I'll put mulch over where I planted it.

The second one still had the wooden bottom of the container stuck to the roots, so not knowing what to do, I put it back in the container. Reading your link, Bitterwort, maybe I should have put the whole container in the ground. Or do you think it would be OK to chop off the ends of the roots so the plant can get detached from the bottom?

Again, thank you for your advice!

Sure, I would just slice the bottom of the roots off to remove the container bottom and then put the root ball in the ground. I have a strong old knife that I use only for garden work in just that way(carefully, no plant is worth slicing your fingers!) In fact, I use it to slice plants out of their pots to bring in the house for the winter--this prunes the roots and I then prune the tops accordingly. Cutting the wooden container off the bottom of yours may encourage new root growth there, especially if the soil doesn't freeze for a while, and root growth is what you want.

I agree heartily with mnwsgal's advice about mulching them to delay freezing the soil in that spot. Keep watering them both too so that the soil doesn't get too dry.

Again, sorry about the mixup!

Hi, bitterwort and mnwsgal

I replanted the one in the container last Monday or Tuesday (I pulled the bottom hard and it came off without using scissors). I put shredded leaves on the soil around the plants. I was able to water them only on that day -- and it is snowing today.... Hopefully they will survive. I'll water them if it gets warm again and the ground gets exposed. Thank you so much for your advice!

Glad to report that my blue salvia survived!! Green leaves are growing. I'll probably keep them in the ground (not put them back in the pots), because of how difficult it was to untangle the roots out of the pots last fall. I'll see how they do where they are now, clay-like dirt worries me a bit (although I think I transferred dirt from the pot in the area around the roots).

Thank you again for your advice!

I'm glad to hear that, Mary Ann. That's very cool! Leaving them in the ground sounds like a great idea too--I expect they'll be very happy. Thanks for circling back.