Cloth beats plastic for frost protection in most garden situations. The plastic vs cloth frost protection debate comes down to one key issue. Plastic touching your plants transfers cold directly to leaves. I learned this lesson after finding black spots on my tomatoes.
Fabric covers plants without causing the damage plastic can. Cloth creates an air pocket between the cover and your plants. That air buffer adds insulation value. Fabric also breathes which prevents moisture buildup under the cover.
Plastic touching leaves during a freeze causes more harm than good. The cold conducts straight through where plastic contacts foliage. Those contact points freeze faster than uncovered leaves would. I saw frost damage exactly where my plastic sheet touched pepper leaves.
Moisture creates another problem with plastic covers. Water condenses on the inside during cold nights. That moisture can freeze on your plants. Frozen water droplets on leaves cause their own damage. Fabric lets moisture escape instead.
This frost cover comparison has one exception. Plastic works fine if supported above your plants. Use stakes or hoops to hold plastic at least 6 inches above foliage. The air gap prevents contact damage. I use PVC hoops for row covers this way.
Old bed sheets and blankets make excellent fabric frost covers. Cotton breathes well and provides good insulation. I keep a stack of worn sheets just for my garden. They cost nothing and work better than plastic tarps for most situations.
Commercial frost cloth falls between plastic and fabric. It breathes like cloth but lasts longer in weather. The lightweight versions let some light through. You can leave them on longer than solid covers. I tested this myself and found plants stayed healthy underneath.
Weight matters when choosing your cover material. Heavy plastic can crush tender plants. Light fabric drapes gently over foliage. I bent several pepper branches before switching to lighter covers. Check your plants each morning for any damage from weight.
Always secure your covers at ground level no matter which material you use. Loose edges let cold air sneak underneath. I use rocks bricks or soil to hold down edges. Trapped soil heat warms plants from below all night.
Pick cloth for most frost protection needs. Save plastic for situations where you can support it above plants with stakes. When I first switched from plastic to cloth I saw fewer dead leaves. Your garden will thank you with healthier plants.
Read the full article: Protecting Plants from Frost That Works
