Opaque and clear slitted covers	Providing additional ventilation by cutting open the row cover supported by re-mesh wire
Tomato leaf protruding through vent slits	Floating cover protecting a 30-foot by 60-foot raised bed plot

Floating covers have a variety of functions based on the weight of the fabric. Lightweight covers are used primarily for insect exclusion; heavier covers are used for elevating day and night temperature; and the heaviest material is used for frost control.

Don't expect crop covers to save your plants from heavy freezes. Row covers and medium-weight floating covers will keep the temperature only 2° to 3°F warmer than the ambient (outside) air. Wind speed and soil temperature influence the degree of protection achieved.

The major benefit of crop covers is their overall growth-enhancing characteristic when used in cool weather. Crops planted one to two weeks ahead of the normal time can mature three weeks early.

Particular attention must be given to cover removal. Depending on the crop and the environmental conditions, row covers can be left in place for about a month. Floating covers can remain in place longer because of their ventilation. Most of the heavier floating covers used for frost control are removed during the day.