How to Use Row Covers

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How to use row covers starts with one question: are you covering plants to keep insects out, to add a few degrees of frost protection, or both? The answer decides the fabric weight, how the cover is supported, and when it comes off. The extension pages checked for this guide, from Maryland, Utah, Washington and New Hampshire, agree on the basics and differ on some numbers. This guide flags those differences rather than smoothing them over.

Quick answer

• Pick the weight first: light fabric for insect exclusion, heavier fabric for frost, with hoops or a frame for the heavier grades.
• Lay the cover over the crop early and hold its edges down with soil, boards, bricks or pins.
• Take the cover off insect-pollinated crops such as squash and cucumbers once their female flowers open.
• Lift the cover to water by hand, or run drip or soaker hose underneath it.

Decide what the cover is for

A row cover is a light fabric laid over or across crops. Maryland Extension describes it this way: “Row cover is a white, lightweight, non-woven fabric made from spun-bonded polyester or polypropylene.” Utah State University Extension notes that row covers are “generally made of spunbond or netted synthetic materials, such as polyethylene, polyester, or polypropylene.” The materials vary, but the job is consistent. Utah State says that “row covers act as a physical barrier that prevents the movement of pests such as insects” to host plants, and that they “shield crops from environmental factors like cold or hot temperatures”.

Weight is the main choice. Maryland Extension lists three grades. The lightweight grade is “marketed as an insect barrier,” and it gives about 2°F of frost protection. The medium-weight grade has 70% to 85% light transmittance and gives 4 to 6°F of frost protection. The heavyweight grade “allows 30% to 50% light transmittance and gives up to 8°F of frost protection.” Washington State University Extension puts the lighter materials on the crop itself and the heavier ones on hoops, which is the practical split this guide follows.

The frost numbers are not identical across pages. New Hampshire’s blog says that “A lightweight row cover might provide 2ºF of frost protection, whereas a heavy-weight row cover might provide as much as 6ºF to 10ºF of frost protection.” That heavy-weight range does not match the 8°F top figure in Maryland’s grade table. Treat any frost number on a cover as an estimate, and check the weight of the fabric you actually own, since the grade boundaries also differ from page to page.

Lay it down early and hold it tight

Timing matters because the cover works best before the pests arrive. Maryland Extension says that “To be effective against pests, row cover must be installed over plants soon after planting and held tightly to the ground.” Washington State describes the same early start from the seedling side, noting that a floating cover “placed over seedlings before they emerge” keeps insects away from tender plants. Utah State adds a plainer rule: growers should “coordinate applying row covers with the targeted pest’s life cycle and the growth stage of the crop.”

Spring transplants are the easiest case. New Hampshire notes that “In the spring, when transplants are small, row cover can often be simply draped over plants without a frame.” That is the floating method, in which the fabric rests on the plants and rises as they grow. Even when the cover rests directly on small crops, Maryland’s standard still applies, so the fabric has to be held tightly to the ground along every side to work against pests.

Edges decide whether the cover does its job. Maryland Extension lists several ways to anchor the cover: “Anchor the cover to the ground with sod pins (also called landscape fabric anchors or staples), wooden boards, bricks, sandbags, rocks, or soil.” New Hampshire makes the same point in its own words, saying that “Row cover should be weighed down – bricks, stones and garden staples are commonly used in a garden setting”. Once the cover is down, check each edge against that standard before you walk away from the bed.

Support the heavier fabrics

Heavier fabric needs a frame. Maryland Extension states that “Using a support is recommended when using medium- and heavy-weight row covers.” Washington State makes the same split, explaining that lighter materials lie on the crop while “heavier materials require hoops to hold the fabric off the plants.” The reason is physical, not just convenience. Washington notes that “plant material touching the cover material could be damaged by frost”, so a frame keeps the fabric off the leaves in cold weather.

Frames can be simple. Maryland says to “Assemble simple frames using wood, slender PVC pipe, #9 gauge wire, or other available materials to support the row cover above the plants.” Utah State describes two set-ups: “Support row covers by hoop structures or by laying directly over the tops of crops needing protection.” If you plan to use the frame for several seasons, Utah State also advises that you consider “whether it will be used for a single season or multiple uses” before you choose the frame material. For a hoop option that many gardeners use, see our guide to PVC pipe for garden bed covers.

Light fabric has its own limits. Utah State warns that “Lightweight row covers tend to rip easily, and thus, have a short life span (up to a few months).” If you need a netting option for pest exclusion rather than fabric, see our piece on bird netting for the garden.

Water through or around the cover

Watering is the step most often forgotten. Maryland Extension advises that “Rainfall and water from a hose or watering can will pass through row cover fabric, but it’s best to pull the cover back if hand-watering.” Washington State agrees that “Overhead watering will permeate the fabric, but drip or soaker hose irrigation is best under the fabric.” Maryland also suggests that you “Use drip irrigation or a soaker hose under row covers to irrigate plants easily and efficiently.”

Some of the water stays in the bed. Washington State says that “Rather than evaporating, water condenses on the underside of the row cover and returns to the soil.” Utah State adds that “Less irrigation may be required under row covers since water collects as condensation on the inside of the cover and returns to the soil.” Utah State also cautions that “However, overall water use may increase since crop growth is earlier and greater and occurs over a longer period of time.” The two effects pull in different directions, so check the soil rather than assuming the cover will save water.

When no drip line is in place, Utah State gives the simplest instruction: “If not using drip irrigation, lift the row covers to allow watering.” Set the cover back and re-anchor the edges afterward, since Maryland’s standard requires the fabric to be held tightly to the ground.

Uncover for pollination and weeds

Insect-pollinated crops need the cover off at flowering. New Hampshire is specific about the cucurbits: “For insect pollinated vegetables, like the nightshades (tomato, eggplant, pepper) and cucurbits (squash, cucumber, pumpkin, melon), row cover should be removed when female flowers bloom so as to allow pollination to occur.” Washington State gives the same principle for its region, saying that the cover should be removed “when the insect-pollinated plants begin to flower”.

Crops that do not depend on insects can stay covered longer. Maryland Extension says that “Crops that don’t need their flowers pollinated by insects, like spring leafy greens and green beans, can be kept covered until harvest.” Weeds are a side effect of the warmth. Maryland notes that “For the same reason row covers can boost vegetable growth, weeds also grow faster under row covers.” Check the bed for weeds when you lift the cover, so they are not left to grow in the dark.

Timing through spring and fall

The cover is a season extender, so it has a start and an end. Maryland Extension says the cover can “enhance plant growth in spring and fall by increasing the temperature and humidity under the cover” and can “extend the growing season in spring and fall by providing 2 to 8°F of frost protection”. Washington State adds that the cover warms the bed directly: “The greenhouse effect warms the soil and speeds up germination, root growth and nutrient uptake.”

The end date depends on the weight and the crop. New Hampshire says that “Once we get to early June, a heavy-weight row cover would no longer be appropriate.” It also states that cool-season crops, such as greens and brassicas, “should typically be removed by early June.” Those dates come from New Hampshire’s climate, so use them as a cue to check the weather and the crop stage rather than as a calendar for your garden. Washington State gives its own window for its medium-weight fabric, with the cover to be “removed early to mid-June,” which again reflects a different region.

Care, cleaning and storage

Cut the fabric to fit before you lay it down. New Hampshire notes that “Row cover can be cut to size using sharp scissors, which is helpful because it typically comes in large rolls of varying widths and lengths.” Utah State gives the same tool: “Cut row covers easily to size using scissors.”

Clean the fabric when it is off the bed. Utah State says that “Row covers can be hosed down with water to clean, but it is important to let them dry completely.” Store the cover dry, because Maryland warns that “Mice can nest in stored row cover material, ruining it for next season.” Clean and dry the fabric before you put it away, so the roll is ready for the next planting.

Mistakes to avoid

• Leaving the cover on squash or cucumbers after the female flowers open, when New Hampshire says it should come off so pollination can occur.
• Putting heavy fabric over a bed with no frame, when Maryland recommends support and Washington calls for hoops.
• Leaving the edges loose, when Maryland says the fabric has to be held tightly to the ground.
• Keeping a heavyweight cover on into early summer, as New Hampshire warns.
• Putting washed fabric away before it dries, which Utah State advises against.

How we chose

This guide uses four extension pages, all opened with curl on 2026-10-23 and all returning HTTP 200. Maryland, Utah State and Washington State are extension publications, and New Hampshire’s entry is an extension blog post. We searched each page for passages on weight, frost protection, support, anchoring, watering, pollination, and storage, and we quoted only sentences found in the page text. Retail listings were left out because they describe products rather than methods. The guide reports the places where the pages disagree, especially on frost numbers and removal dates, and does not average them into a single figure.

What we could not verify

The pages do not give one set of rules for every crop or climate. Frost protection, light loss and removal dates depend on the local weather, the crop, and the weight of the fabric you own, and none of the pages measures those factors for a specific bed. The pages also place the boundaries between weights differently, so a fabric labeled with one grade may fall into another page’s category. The pages were not written at the same time, so newer fabrics or practices may be missing from this guide.

What the sources do not say

The pages do not agree on heavy-weight frost protection. Maryland gives up to 8°F, while New Hampshire gives 6°F to 10°F. The pages also give different removal dates for different regions, and none offers a single date for every garden. Washington State and Utah State both describe condensation that returns water to the soil, while Utah State also warns that overall water use may increase. None of the four pages says how much water a cover saves. This guide does not supply that figure.

Frequently asked questions

Is a light or heavy row cover the better choice?

Choose light fabric when the main job is keeping insects off young crops, and choose a heavier grade when frost is the concern. Maryland and Washington both place the heavier grades on a support, so plan the frame before you buy the fabric. Check the weight of the fabric you own, because the grade boundaries are not the same on every page.

How can insects be kept from getting under the cover?

Set the cover down early, before pests appear, and hold it tightly to the ground. Anchor every edge with soil, boards, bricks, rocks or pins. Maryland’s guidance lists those anchors and also says the fabric must be held tightly to the ground to be effective against pests.

When should the cover come off a cucumber or squash bed?

Remove the cover when the female flowers open so that pollinators can reach them, as New Hampshire explains for cucurbits. If the plants do not depend on insects, such as leafy greens and green beans, Maryland says they can stay covered until harvest.

Can a crop be watered with the cover still on?

Rain and hose water pass through most fabrics, but Maryland recommends pulling the cover back for hand watering. Drip irrigation or a soaker hose under the cover avoids that step, and Washington notes that these are the best options under the fabric.

Can a row cover be reused next year?

Lightweight fabric tends to rip, and Utah State gives it a life span of up to a few months. Wash the cover if needed, let it dry completely, keep it away from mice, and inspect it for tears before each use.

Sources

• https://extension.umd.edu/resource/vegetable-garden-weather-and-pest-protection (opened 2026-10-23)
• https://extension.usu.edu/planthealth/research/row-covers (opened 2026-10-23)
• https://s3.wp.wsu.edu/uploads/sites/2076/2024/07/C187-Row-Covers.pdf (opened 2026-10-23)
• https://extension.unh.edu/blog/2020/10/using-row-covers-garden (opened 2026-10-23)

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