Wednesday, April 14, 2021

Row covers protect spring and fall gardens

by Mark Amara, WSU Grant-Adams Master Gardener
| March 28, 2021 1:00 AM

In a year like 2021, floating row covers may provide ways to get a jump on the outdoor gardening season earlier or extend it longer.

Season extenders come in all shapes, sizes, materials and thicknesses. They are used for frost protection, insect or other critter control (like birds, squirrels or rabbits), for passive heat and to maintain more uniform growing conditions in erratic weather (which sometimes occurs in the Columbia Basin).

Row covers can be used early in the spring or in the fall. The products best suited to temperature variations or extremes provide some protection from freezing, are good heat insulators and may help keep insect pests from plants.

They are typically made of synthetic polypropylene or woven polyester that allows water and air to move freely through them. Plastic may also serve as a passive heater cover. However, plastic does not breathe, nor does it allow air or water in unless opened on the ends or with an irrigation system, like a drip system, that provides water under it.

With the exception of plastic, materials come in different thicknesses and weights, which vary in the amounts of light and heat that they transmit. If row covers are carefully handled, they can be reused over multiple years.

Lightweight row covers allow 90% light through, and are often advertised as insect barriers but are not intended to serve as frost protection. These materials are very thin and may rip easily. So, they are generally not reusable after they rip.

Medium-weight row covers allow 85% light and frost protection to 28 degrees Fahrenheit.

Heavy row covers allow 35% to 50% light through and frost protection in the 24- to 28-degree range.

All types of row covers should be cleaned or hosed off to keep soil from adhering to them. Without proper cleaning, materials tend to break down more quickly.

Be sure cover materials are thoroughly dry before storing to keep them from molding or breaking down further.

Row covers are usually sold 5 feet to 50 feet in width and may be up to 1,000 feet in length. They are laid directly over plants or over support structures made of aluminum, PVC or plastic hoops and anchored with soil, rocks or other heavy objects.

If using them for insect protection, check to be sure insects are not present on plants before and after covering to reduce infestation issues.

For example, in my Moses Lake vegetable garden, I often use both the lighter insect covers and heavier frost protectors supported by wire hoops for different situations.

I anchor the fabric to the ground with wood or steel fence posts rather than by soil so it can be easily removed and it reduces opportunities for weeds to proliferate on the edges.

Row covers are generally resilient when it comes to irrigation. Ideally, drip irrigation works the best, though overhead sprinkler irrigation works fine, since materials (except plastic) are usually quite permeable.

Once plants are established in the warmth of spring, the frost protection covers can be removed. Alternatively, they can be left on for pest protection or used to re-cover plants later in the fall when cold temperatures threaten.

For answers to gardening questions, contact the WSU Grant-Adams Master Gardeners via email at or visit