As summer vegetables finish their season, cooler temperatures signal the end of their growing time.

If frost comes before the last tomatoes turn red, a gardener can put a thin fabric sheet over their cages.

This keeps the plants warm.

These white sheets are sold as row covers.

They can be used in two ways: floating over plants or attached to hoops in the ground.

The hooped method protects weak stems and leaves better.

The hoops stop the fabric from crushing plant parts.

Row covers also protect cool-season vegetables like spinach, radishes, cucumbers, potatoes, kale and lettuces.

The UV-protectant sheets cannot do miracles.

But they can raise the temperature around plants by up to 8 degrees F.

That can mean the difference between life and death.

Row covers come in different sizes and can be cut to fit.

They are sold in three weight grades.

Lightweight materials offer only a couple degrees of protection.

So they are mainly used as insect barriers in spring.

They let about 90% of sunlight reach plants.

Heavy fabrics give the most warming but block sunlight and water a lot.

They also risk making the temperature too high.

Medium-weight fabrics balance the two.

They let 70% to 85% of sunlight through and warm the air by 4-6 degrees F.

This can allow several extra weeks of growing time.

Floating covers should be put loosely over low-growing plants.

They are held down by burying their edges or placing stones or bricks along the sides.

Leave enough slack for plant growth.

For taller or more fragile crops, gardeners can buy ready-made hoops.

They can also bend flexible PVC piping into upside-down U shapes and put the ends into the soil.

Covers can go over a single plant, a whole row or a raised bed.

Plants still need checking: check soil moisture, remove covers when flowering plants need pollination, and pull covers back on warm days.

This stops the vegetables from cooking before harvest.