Any problems with frost heave in spring?

This spring I plan to put out some vegetable sets, such as broccolii and cabbage, in early April in my SFG. I just read in Wikipedia that silty and loamy soil types, which contain fine particles, were examples of frost-susceptible soils. Peat moss certainly contains many fine particles and so does vermiculite. Frost heave refers to the tendency of plants to be heaved out of the soil due to frequent freezes and thaws as happens sometimes in March and April. I remember losing some young poppy plants in April after a strange weather pattern. It looked as if someone had pulled the young plants out of the ground by hand. The freezing temperatures then killed the plants.

Is Mel's Mix susceptible to frost heave? I hope not because these sets are pretty expensive.

Frost can kill plants regardless of heave. If you are worried about your sets, you might wish to delay setting them out until you determine that your area is safely frost-free. That, or set up a row cover or other protection per your needs.

Fortunately SFGs like all raised beds do stay warmer than the surrounding native soil. Mel's book (page 167, new book) advises covering the box with black or clear plastic in early spring for a few days to help it warm up, turn soil, rinse and repeat.

I had no problems with heave when I put my plants out in April, in fact they are still going strong. Heaving comes with deep soil freezing, not frosts. IF the plants appear to be heaving, just push them back down either with your hand or by foot above the root system. Simple.

My guess about your poppies was a shallow root system, along with the weather, led to their demise.