Start your annuals later in the spring. Here, i start in mid to late April and into May. You might be able to start a little earlier. I have had to cover, and i've had to bring containers indoors because we've had a few lousy Mays, but it beats fussing with everything under lights and paying a big hydro bill. :)

I've put containers into my cold frame and put tarps or blankets over that, and the same with the mini-greenhouse. Your plant cart should work fine.

Also, look for "half-hardy" or "hardy" annuals. You will have less trouble with these. Things like lobelia, nicotiana, marigolds, dusty miller, snapdragons etc. are more forgiving of a couple of cold nights than very tender annuals.

It pays to do some research into how fast your annuals will mature when wintersown. Some will flower much later than greenhouse grown plants, or not have time at all.

I am in Zone 5 and did my annuals mainly in March...morning glorys, poppys, bach buttons and powderpuff asters....all bloomed but to be honest I think I should have put the morning glorys somewhere sunnier...Of course you can not plant them out till after the last frost same as store bought ones.

I do most of mine in late March/early April too, especially if they are new to me or tender annuals. Zinnias go out even later.

If you know that some reseed in your gardens or are 'hardy/half-hardy' as Northspruce states, put those out earlier. Such things as Bachelor Buttons can take a mean frost - even an ice storm! A couple of years ago we had an uncovered container of BB sprouts which got hidden under 2 inches of ice pellets and came through.

I have large heavy plastic containers which I used to cover things up if there's a mean frost on the way. Sometimes I forget to place it on, and most times things have done fine.

Thanks so much everyone, I am gonna try some annuals, Alyssum and Calendula, maybe some more, the annuals I really want I'm still gonna do those indoors, It wouldn't be the same without the longer bloom period and some do take quite a few weeks to set buds. I have at least 20 different perennials outside already, and about 20 different kinds indoors started already. So if the winter sowing is somewhat successful, that will be just fine. Janet