Although grown as an annual in gardens across the United States, tomatoes are tender, warm-season perennials that require protection from frost. In southern gardens, tomatoes may ripen fully on the vine before cold weather returns, but in northern climates, green tomatoes may linger well into the fall. To extend the growing season and provide tomatoes an opportunity to ripen on the vine, many gardeners cover tomato plants with blankets or sheets when frost threatens in the fall.
Spread the sheets to cover all areas of foliage. Edges of leaves or tips of stems exposed to the air risk damage from frost.
Anchor edges of the sheet with rocks or sticks to prevent winds from uncovering the plants or exposing tender foliage.
Remove sheets in the morning once the sun has risen and temperature climbs to allow the sun to shine on the tomato plants.