I hung shade cloth over my 24" plants, and piled straw around my others...with little fluffy straw toppers. This will make taller plants bend and curl though if there's rain or snow, so I only use it if the forecast is for clear and calm. If it's cloudy at daybreak and remains so for an hour or two after, or wet, they might be okay anyway. In my mind, it's that fast warmup of morning sunlight on frosted leaves that causes the most damage.
