Average last frost date, I meant.

Bachelor buttons are tough. I'd go ahead and plant out in the garden. Do not put them inside under lights!!! That would ruin the wonderful simplicity that is wintersowing.

Martha

I haven't grown Bachelor's buttons, but if they're an early sprouter they're probably pretty hardy, so it's possible that they will be okay if you transplant early, especially in zone 7, as long as the soil is workable.

Sometimes I will pot seedlings up into small pots, cups, or flats to grow on outside, before being ready to transplant in the garden or perhaps to bring to a swap or something. You can put the seedlings in pots until you think the weather is better for planting.

This is only my 2nd year wintersowing and I didn't try Bachelor's Buttons last year so don't have a direct comparison. I did wait quite a while to transplant from my wintersown containers because we have such crazy weather in CO, we actually had quite a bit of snow and very cold nights in May last year. I waited until almost the end of May to transplant and quite a few of my seedlings were large, starting to crowd up to where the gallon milk jug gets narrower, some a good 4-6 inches high, but had no problems transplanting them. Some had grown quite thick; had to break a matt of seedlings into sections rather than put down individuals but they did great. I had all of my containers on a raised deck under partial cover and pulled back the tops every warm day and kept up watering from the bottom. Even left in the jug that long I was amazed that I didn't have leggy seedlings; they were nice and bushy and healthy looking, enough to make a wintersowing convert out of me! Especially when I compared them to the wimpy mail order seedlings I was planted them with! No mail order seedlings this year (but I did break down and order lily bulbs).

Bachelor buttons are pretty hardy, and could probably withstand being planted out now. If you are uneasy about doing that yet, you could do as terrene suggests and re-pot to larger containers - maybe big plastic cups or some such. Or, you could just leave them where they are (what type of container are they in now?) and give them a very weak feeding. My records say that I've planted out bachelor's buttons in the first few weeks of April each time I have sown them (and they have germinated at various times in February /March).
Where is 7a are you? I have to change my zone designation since I'm now in zone 7 (NYC). Personally, I'd wait to plant them out for another week or two - you don't have to wait until your last frost date.
Whatever you decide to do - DO NOT put them inside. If they were to survive under lights inside, you'd have to deal with all that hardening off, which defeats the idea of winter-sowing.
Good luck!

PV

Thanks all for the suggestions! I am nowhere near ready to put them in the ground yet (bed isn't ready yet) and some I will probably take to a swap meet that's coming up in the next couple of weeks. So I think this weekend I will just transplant them into some 18oz Solo cups, which I have a bunch of thanks to a visit last weekend to Costco, as a temporary measure until I'm closer to getting ready to put them in their final spot.

The weather will still be a wild card for a while yet (forecast to freeze overnight the next two days for instance) but I'll just have to watch it and bring them onto the porch if it looks like it's going to freeze overnight.

PV, you asked what kind of flat they're in - it's basically a large but relatively shallow (maybe 4-5" tall) takeout container. So they're threatening to bust out at this point (though I have taken off about half of the top covering as it's gotten a little warmer here).

I'm in Washington, DC, not too far from you.

Here's a picture of the flat I took on March 9th (they've grown a bit more since)

Here is a link that might be useful: Bachelor Buttons flat

2010 was my first year wintersowing. I've grown BB's every year. Our average last frost date is about May 22, and the "safe" plant out date is May 30. We continue to get snow as late as the third week of May. In 2010 I was in a different location. Same city but downtown which is a solid zone 6, due to different elevation plus the thermal mass of the pavement and buildings. In 2010 I planted out April 15 when the sprouts hit the top of the container. In 2011 I planted out May 15th, and in 2012 May 5th. The earlier plant-outs bloomed better than the May 15 planting.

Your seedlings are half-hardened. They are already fine in whatever temperatures you have right now. If you haven't had the top of your containers open, they may be a bit soft to go directly out into the wind. Gradually expose them to wind, rain, sleet, etc, and they will be fine. You can plant them in the ground now and put cloches over them to protect them from wind. Easy cloche: milk jug with the bottom cut off, held in place with a stick through the hole where the cap goes. Remember to uncover them for a while each day so the wind can help them get strong.

Kwolfe, your problem is one reason I favor the milk jugs and 2L containers -- they have more headroom to grow. That said, I've often had plants grow to the very top all crowded together and they've survived until May when I planted them out. As long as they've got enough water they should be fine.