Best Row Covers for Cabbage Moths and How to Use Them

What are the primary physical differences between floating row covers and insect netting?

Floating row covers are typically made of lightweight, non-woven polypropylene that creates a microclimate by trapping heat and moisture. Because this material is opaque or translucent, it restricts airflow and light penetration significantly. In contrast, insect netting is a woven, monofilament fabric designed specifically for high ventilation. It acts as a physical screen rather than a thermal blanket, allowing rain and wind to pass through while still excluding pests.

A common example is using a heavy-duty spun-bonded cover to jumpstart early spring growth, which effectively warms the soil but risks overheating the cabbage once temperatures rise. An exception occurs with ultra-lightweight, high-transmittance netting that provides minimal thermal gain but offers superior pest protection throughout the entire growing season. This distinction is vital because choosing the wrong material can lead to stunted, heat-stressed plants that fail to head up properly.

How does the weight and light transmission of a row cover affect cabbage development?

Heavier covers often cause cabbage to become leggy or soft due to reduced light intensity and trapped heat.

• Light transmission: Standard insect netting allows roughly 85% to 90% of sunlight to reach the leaves, which is sufficient for robust photosynthesis.
• Leaf density: Excessive heat under thick covers can lead to loose, airy heads instead of the tight, dense structures desired in varieties like Savoy or Danish Ballhead.
• Moisture levels: High-density covers often retain too much humidity, which can encourage fungal pathogens or rot on the lower leaves.
• Growth rate: Properly ventilated netting maintains a natural growth rhythm, avoiding the rapid, weak stretching often seen under heat-trapping fleece.

What is the optimal timing for installing row covers to prevent cabbage moth egg-laying?

Install covers immediately after transplanting or as soon as direct-sown seedlings emerge. Cabbage white butterflies are active as soon as daytime temperatures reach 55 degrees Fahrenheit, so delaying installation by even a few days allows them to deposit eggs that will hatch and destroy your crop within a week.

How can gardeners effectively secure row covers to prevent moths from crawling underneath?

Securing the perimeter requires a complete seal, as moths are adept at finding small gaps. Using heavy-duty landscape staples spaced every 12 to 18 inches is a standard practice for keeping the edges flush against the soil. For uneven ground, you can use sandbags or heavy timber to create a continuous weight that conforms to the terrain. This creates an impenetrable barrier that prevents the insects from fluttering underneath the fabric.

One nuance involves the use of soil trenches. Digging a shallow furrow, placing the edge of the netting inside, and backfilling it with dirt provides a more reliable seal than surface weights alone. An exception to this rule is during heavy rain, where soil might wash away from the trench and create a gap. Regular inspections after storms are necessary to make sure the seal remains intact throughout the season.

What are the long-term impacts of using synthetic row covers on soil temperature and moisture levels?

Synthetic row covers generally increase soil temperature by 3 to 5 degrees Fahrenheit while slowing evaporation rates significantly.

Use these figures to gauge how often you need to check soil moisture levels, as covers that retain more water require less frequent irrigation.

Are there specific environmental conditions that make row covers more prone to tearing or degradation?

Yes, high-wind areas and intense ultraviolet exposure significantly shorten the lifespan of synthetic covers. Thin, 15 gsm fabrics often begin to degrade or tear after 500 hours of direct summer sun, necessitating replacement every season to maintain the integrity of the pest barrier.

How should row covers be managed to accommodate the pollination requirements of surrounding garden plants?

Row covers must be removed during the flowering phase if you are growing companion plants that require insect visitation.

• Pollinators: Bees and hoverflies cannot access nectar sources if the netting remains in place, which can reduce yields for surrounding crops like squash or peppers.
• Companion plants: Flowers such as alyssum or marigolds planted near cabbage to attract beneficial insects will be rendered useless if they are trapped under the netting.
• Hand pollination: If you must keep the netting on to protect the cabbage, you will need to manually pollinate any nearby flowers using a small brush.
• Timing: Remove the covers only during the specific window when your companion plants are in bloom and the cabbage is large enough to resist minor pest pressure.