Sitting at room temperature in CostcCo they have become "forced" and sprouted prematurely. So now you have to keep the unseasonal new growth protected from frost. Maybe waiting until after the nights in the 20s F. predicted for the next few days are over and then planting out with some moderate protection like those waxed paper "hot caps" to hand would get you by.

When I've bought packaged perennial roots locally in order to get specific varieties without hunting around for them I've found the divisions to be small and weak. Treasures brought from the NW Flower & Garden Show and planted here on Camano threw up one or two tiny shoots and then disappeared. This includes items like astrantias and day lilies that are ordinarily quite willing.

A packaged Rheum chunk I bought there this year turned out to be small, rubbery and bearing a couple small shoots off to the side - in other words looking like more of same.

I've also gotten bags of under-sized bulbs off the racks at CostCo. It seems suppliers cannot be counted on to send top grade material when it is packaged and more or less out of sight (the sprouting packaged perennials at CostCo can be seen to be dinky right on the racks); so whenever possible it is preferable to buy roots, bulbs or growing plants that can be examined before purchase.

You take the same risk with mailorder. Stock coming through the mail can be be found to be dismayingly small when received.

If you can put them in a garage, basement where the temperatures are well above zero and you have some lights you could put them temporarily in pots until the weather in our beautiful Vancouver improves.I think you can remove the sprouts if you don't want to plant in posts and they should sprout again from different areas.YOU would loose them if you plant now.Its far too cold.

Thanks a lot guys! Yesterday I planted them in pots and put them in my garage.
For the Clematis and Peony, I'll let them stay in pots until fall. And I'll transplant Astilbe as soon the weather turns better. Thanks again everybody.

Removing sprouts from already minimal divisions could produce failures. This seems especially likely with a peony, which produces a single set of shoots once per year.

Keeping them in pots all summer may prove less satisfactory than getting them back into ground this spring.

There's no compelling reason to keep the peony in a container all summer - the oft-heard recommendations that these should only be planted in fall don't have anything to substantiate them. The plants grow just as successfully with spring planting.

But there ARE good reasons to hold the clematis. They are most successful when transplanted as 2 or 3 year old plants and have already developed a good substantial root system. Bare root plants are usually quite young and with minimal roots. Growing them on in a container for at least a season will increase their chances of success and you can give them the individual attention they will need. You might want to check out the Clematis forum for confirmation and specific planting/growing techniques.

Exerpted from Gardening with Clematis:
If you do find that you must buy a small or bare-rooted plant to get the form you want (or if the price is simply too good), transplant it into a one-gallon-size pot before transferring it into the garden. Let the clematis stay in this pot as long as it takes to get it into "fighting trim." A clematis should have a large root mass and strong new shoots before venturing into the ground. Small plants put to earth too soon will simply dissolve away, never to be heard from again. Strong plants will grow boldly once they are placed in your soil and given proper support.

Assuming you can provide better conditions in a container. Some people will have more trouble keeping potted stock watered and fertilized than they would a plant in the ground - where it belongs.

Slugs are also a factor here. Tiny hybrid clematis specimens need to be located where they will not be destroyed by them.

The bulbs I bought from Costco the year before last weren't true to the label...I won't do that again. They were supposed to be Oriental Lilies but they were Asiatics.

In this case, I'll keep Clematis in pots till fall. Thanks!

Use large containers and be sure to plant with a section of stem above the crown buried.