Hmmm. The problem is the forecasters are not that accurate.....and 34 can turn into 30. That "25" forecast may be too low. Cardboard or upside down pots or similar may help in the borderline freezes. You may want to put a bottle of hot water (e.g. empty milk jug) under the box with them to throw off a little heat. Cold wind coming in at the time of the temp drops also can cause havoc. If there are not too many plants and you can dig them back up (Since they were recently planted they are probably not rooted in well yet) maybe you can put them in a temporary tray/pot in protected garage or basement and replant them next week when temperatures return to "normal".

mothers day or the third week of may is usually the MI time to plant ..

yes.. cover them ... i wouldnt bother with the plastic .. but if you can remove it every morning.. it probably wouldnt hurt ...

the simple equation is actual frost or ice on the leaf itself .. hence covering it ... it doesnt matter with what.. but best if you can keep the cover from touching the leaf itself.. so cold cant transfer thru ...

and the heat of the soil in the barrel.. should probably give you the few extra degrees you need to protect them ..

a little cold.. or frost.. usually wont KILL the plant.. they might just not be pretty until they outgrow the damage... what you really need to worry about is a FREEZE ... there is a big difference between a frost and a freeze.. that our warmer zone peeps dont get ...

ken

If it's only a few plants, it might be easier to just temporarily pot them back up and move them to a protected area until the correct planting time.

Ken, even those of us that can leave tropicals(like cannas, crinums, palms, gladiolus,etc) outside over winter, do know the difference between a frost and a freeze. We still get both of those ;)

Yes, if 25, I doubt much that you can do short of bringing inside. It's dependent upon what you planted (snapdragons for instance should be able to take it). The ones you mentioned...no.

Yep, they need to be covered to protect from frost. Another problem is that daytime temps aren't forecasted to get out of the 50s for a few more days at least (haven't looked far ahead yet), and lucky if gets into mid-50s here in MI. What that means is *soil* temps are not warm, and that leads to problems -- namely stunted root growth and potentially rot. WAY to early for annuals up here in MI -- consider it a lesson learned, and for now cover at night and better yet take the above suggestion to dig them up and replant at the appropriate time. If you don't go that route, consider some draping with some plastic sheeting with ventilation holes that will concentrate the heat and warm the soil for the time being.

I have covered them the last 2 days with the cardboard boxes. Should I keep them covered during the day also?

^^ I would if it is windy or really cold -- it's weather dependent. But if temps in 50s they'll be ok during the day, and the more sunshine you can expose them to the better (to warm the soil at this point). Definitely cover them at night if you're not going to dig and bring back in. Supposed to be record low temps. Brrr...

Should I keep them covered during the day also?

===>>>NO!!! .. you are making a relatively warmer hot house.. and encouraging faster growth.. which will be more tender to cold damage ...

uncover them as the day warms ... they should be rather acclimated to usual 40 degree F plus temps ... presuming they were properly hardened off ...

ken

We're expecting 30 degrees tomorrow night and forget the annuals (as if--I planted them too early, too)--I'm worried about the hostas! I read somewhere to place a flowerpot upside down over the plants, so I"m going to try that. I also would consider putting a box in the middle of a bed and spreading a sheet over it (the box would keep the sheet from sitting directly on the plants) and weighing it down with rocks. Come ON....Spring!!!!

We're getting down to 25 overnight. Should I be covering all the perennials? Hostas, huechera, ferns?

You can, but at what point do you stop being a slave to the garden and worrying about every little weather change? Sure there are a few things I give special attention to (at the moment -- my potted fruit trees), but just that -- a few, and a very few at that. They're plants for goodness sake, they'll be fine if they're zone-hardy perennials. By fine I mean they'll survive -- may get tattered or leaf burn but cold night temps are not going to kill them. This is hard thing to let go of -- this mentality that we have to baby everything out there. Believe me I know, I used to be that way, but after gardening for a few years I realized the plants don't need me to coddle them in order to do well. They have an innate desire to survive and reproduce -- and they will. So cover what's "prime" to you and let the rest be what it's going be.

Now, annuals and warm-season vegetables are a whole other story -- I think you got the primer on that in the above posts.