As someone else who gardens in a cold climate with a short growing season, I tend to agree with Flora - you started your beans too early. Your bean transplants are nearly ready to go into the ground, with warm weather still weeks away. While I can direct seed most common beans here with a good chance of success, I use a lot of bean transplants. For heat-loving beans such as limas & yardlongs, transplants are virtually necessary in my area to ensure a good harvest. It is also good practice to use bean transplants if you have limited seed or temperamental Spring weather, since it overcomes cool-soil germination issues & means that nearly every seed which germinates will survive. And if growing a bean for seed, it increases the chance of getting dry seed before wet Fall weather arrives. I would never use flats filled with soil though, for the reasons given in the OP. My preferred method is to use peat strips, with sterile soil less mix. Planted pot & all, this avoids root damage during transplanting. 32's work well for larger beans, and 50's for smaller beans & Vignas (cowpeas, yardlongs, adzuki). To further lessen transplant shock, place a little sand in the bottom of the tray & nestle the peat strips into it after planting. Provided the sand is kept moist (but not overly wet) those long bean roots will not be air pruned, but will grow into the sand. At the time of transplanting, those roots can be gently pulled from the sand. Working quickly to keep the roots from drying out, gently coil them into the hole beneath the plant, then water immediately. I have had virtually no transplant shock using this method. As a rule, I consider beans to be ready for transplanting when they have their first true leaf. This generally takes about 2 weeks, so I start bean transplants that much earlier than the recommended date for direct seeding. If transplanting is delayed by bad weather, I've held bean transplants up to a month before planting. Much beyond that, though, and they will become stunted. For squash & cucumbers, I use the same procedures as above, except I omit the sand. It is worth noting that it takes an intense light source to grow beans, cukes, and squash indoors, or they quickly become leggy... shop lights are not up to the task (spoken from experience). If at all possible, those transplants should be placed in direct sunlight as soon as possible after germination.

Been my experience that established tall garden phlox shock easily when transplanted. Also been my experience that all of a sudden they settle in and perk up. If the weather does dry out, keep them watered. They're pretty hardy and you shouldn't loose them - especially since you transplanted them in a clump rather than trying to separate the individual stems.

While it won't help for any possible cold damage done up until this point, I second the frost cloth suggestion. I'm in the inland empire, and have 6 in-ground plumeria in the back yard. They've been covered with frost cloth since the first cold spell, and it seems to be working. I didn't do the frost cloth thing last winter until too late, and ended up having to amputate several branches of one of the plumeria the following spring to save it from rot. I don't do anything really fancy - I just buy the long garden stakes at Lowes (6'ish) and stick them in the ground around the plumeria, then throw the frost cloth (also from Lowes) on top and secure it with clothespins. The cloth should touch the ground on all sides. The plumies still get some airflow and light, but the cloth keeps it slightly warmer underneath. I agree with everyone else that you should probably leave it alone (just protect it from future cold spells). Keep an eye on any branches that you think might have damage, though, and if they start feeling mushy, you may need to take action.

Did they overwinter in your garden? Or did you just plant them like a week or two ago? I grow Sasa Palmata bamboo and a harsh winter turns the leaves dry and lifeless and they fall off- BUT- the roots grow new plants back rapidly. This winter was mild and so they stayed green, but last winter I had to cut them down and let the roots grow new plants. Another experience I had - someone gave me a small bamboo plant and I was new to growing it and the newly transplanted bamboo did not get enough water and by winter it looked like your photo and it didn't make it. ps.. And I just read your post again ... Some of your roots might live but big tall bamboo plants like yours need an extensive root system to survive at that tall size and it's doubtful you got enough root to support it. I made that mistake also with some Black Bamboo.