I am surprised you can already plant in Kansas. I haven't walked through my back yard since Dec due to knee high snow. The piles are starting to melt a bit, but it will be a long while before the soil un freezes. Maybe by the end of April I'll be able to get the cole crops going, but I doubt it will be before then.

Ugggggh! mandolls!! My older sister lived in WI (Madison/Beaver Dam) for 15 years & never adapted to WI winters! Kansas winters can be brutal, but we can't compete with WI!

I've got my brassicas under low tunnels & we're supposed to be down to 20F tonight...... Agribon protects to 26-27F, so I may be replanting!

The good thing is that all of those veggies except the potatoes are quite tolerant of mildly alkaline soil.
Properly hardened off, your arugula, radishes and spinach will shrug off 20 F no problem. Damage won't start showing up until it gets below about 15 degrees. Don't be alarmed if the cotyledon leaves get burned by a freeze - this is normal.

Pea plants are good down to about 20 degrees.

Lettuce doesn't like it if it gets below the high 20s F, so I would focus on protecting that.

Edit: just reread your post and realized you sowed them today, so it doesn't really matter.

This post was edited by Slimy_Okra on Sun, Mar 16, 14 at 21:29