Quick Answer
Cutworms are nocturnal larvae that chew through seedling stems at the soil line, often killing transplants overnight. The most reliable defense is a physical collar placed around each stem when you set out seedlings. Simple DIY collars made from cardboard, plastic cups, or toilet‑paper rolls stop cutworms from reaching the tender tissue.
Install the collar so it extends at least 2 inches above the soil and 1 inch below the surface, creating a barrier that the larvae cannot climb or burrow under. Check the collars each morning for signs of damage and replace any that have been compromised. This method works for brassicas, tomatoes, peppers, and many other vulnerable seedlings.
Because cutworms feed primarily at night, a nighttime inspection with a flashlight can confirm activity, but the collar itself eliminates the need for nightly patrols. Combine collars with good garden sanitation—removing weeds and plant debris—to reduce hiding places for the pests. The result is a noticeable drop in seedling loss, often from 30 % or more down to under 5 %.
In short, a quick, low‑cost collar gives you immediate protection while you address the broader habitat factors that encourage cutworm populations.
Why This Matters
Seedling loss to cutworms can undo weeks of careful propagation, especially for high‑value crops like broccoli, cauliflower, and cabbage. When a transplant is severed at the base, the plant cannot recover, forcing you to re‑seed or purchase new starts. This delay pushes back harvest dates and increases labor costs.
Cutworms are especially problematic in early spring when soil is still cool and moist, conditions that favor larval activity. Gardens that have been recently tilled or that contain abundant organic mulch provide ideal shelter for the larvae. Without intervention, a single night of feeding can wipe out an entire row.
Beyond the immediate loss, cutworm damage can create gaps in plant spacing, leading to uneven canopy development and increased weed pressure. Gaps also make irrigation less efficient, as water runs off bare soil instead of being taken up by plant roots. Maintaining a uniform stand helps preserve soil moisture and reduces the need for supplemental watering.
Financially, the cost of replacing seedlings or losing a portion of the harvest can outweigh the minimal expense of making collars. A typical cardboard collar costs less than a cent per unit, while a lost tomato transplant may represent several dollars in potential yield. The return on investment is therefore high, even for small home gardens.
Finally, using collars reduces reliance on chemical controls, which can affect beneficial insects and soil health. A mechanical barrier is selective, targeting only the pest that tries to climb the stem, and leaves predators like ground beetles undisturbed. This aligns with integrated pest management principles that favor cultural and physical tactics first.
Step-by-Step Guide
Gather your materials: stiff cardboard (from cereal boxes or shipping tubes), a pair of scissors, a ruler or measuring tape, and a marker. If you prefer reusable options, cut sections from clean plastic cups or toilet‑paper rolls. Ensure the material is free of inks or coatings that could leach into the soil.
Measure and cut a strip that is 4 inches wide and long enough to wrap around the seedling stem with a ½‑inch overlap. For most seedlings, a 4‑inch length provides a 2‑inch collar above ground and a 2‑inch portion to bury. Adjust the width if you are working with larger stems, such as those of squash or melons.
Form the strip into a cylinder, overlapping the edges by about ½ inch, and secure the joint with a staple, a paper clip, or a small piece of tape. The cylinder should be rigid enough to hold its shape when pressed into the soil but flexible enough to slip over the stem without damaging it.
Before transplanting, prepare the planting hole as usual. Place the seedling in the hole, then slide the collar over the stem so that the bottom edge sits about 1 inch below the soil surface. Gently firm the soil around the collar to eliminate gaps that a cutworm could exploit.
Check that the top of the collar extends at least 2 inches above the soil line. This height prevents the larva from climbing over the barrier. If you notice the collar sinking after watering, add a little more soil to maintain the proper depth.
For added durability, you can coat the outside of the collar with a thin layer of beeswax or a natural latex solution. This makes the cardboard more resistant to moisture breakdown while still allowing it to decompose at the end of the season. Avoid synthetic sealants that could hinder soil aeration.
After installation, monitor the seedlings each morning for any signs of wilting or stem damage. If a collar appears chewed or displaced, replace it immediately. Consistent monitoring during the first two weeks after transplanting catches any early breakthrough before it spreads.
When the plants have established strong stems—usually after three to four weeks—you can remove the collars if desired. Leaving them in place does not harm the plant, but removing them reduces potential shelter for other pests and allows better air circulation at the base.
If you prefer a ready‑made option, commercial collars are available, but the DIY method described here costs virtually nothing and can be scaled to any garden size. For further reading on seedling health, see our guide on preventing damping off: Prevent damping off seedlings.
Best Conditions
Cutworm collars work best when the soil is moist but not soggy, as overly wet conditions can cause cardboard to disintegrate quickly. Aim for a soil moisture level that feels like a wrung‑out sponge—damp enough to hold shape when squeezed, but not dripping.
Ambient temperatures between 50 °F and 75 °F favor cutworm activity, making early spring and late summer the peak periods for collar use. In hotter weather, larvae may burrow deeper, but the collar still blocks surface access.
Full sun exposure helps the soil dry quickly after rain, reducing the time cardboard remains wet. If your garden is shaded, consider using a more water‑resistant material such as a plastic cup collar, which holds up longer under persistent dampness.
Soil texture influences how easily the collar can be inserted. Loamy or sandy soils allow the collar to slide in with minimal resistance, while heavy clay may require a slight widening of the hole to avoid tearing the material. In clay beds, a short pre‑soak of the cardboard can make it more pliable.
Finally, avoid placing collars directly against fresh manure or uncomposted compost, as the high nitrogen content can accelerate breakdown of cardboard. A thin layer of finished compost or straw mulch around the base is acceptable and can even help retain moisture without compromising the collar.
Seasonal Timing
Begin installing collars as soon as you transplant seedlings outdoors, which for most temperate zones falls between mid‑March and early May. This timing coincides with the emergence of overwintering cutworm larvae that become active as soil temperatures rise above 45 °F.
For succession plantings, such as a second round of broccoli in late summer, reinstall collars at each transplanting event. Late‑season larvae are often smaller but still capable of severing young stems, especially when soil remains warm into September.
In regions with mild winters, cutworms may remain active year‑round. In these areas, consider keeping collars on perennial vegetables like artichokes or asparagus until the plants develop woody stems that are resistant to chewing.
Monitor local extension services or gardening forums for cutworm alerts; many regions publish weekly pest activity reports based on pheromone traps. When reports indicate a spike in larval catches, double‑check that all new transplants are collared and inspect existing collars for wear.
If you miss the initial window, you can still add collars to established seedlings, though effectiveness drops if the stem has already begun to lignify. In such cases, focus on cultural controls—removing weeds, turning soil to expose larvae, and applying beneficial nematodes—to supplement any physical barrier.
Common Mistakes
One frequent error is making the collar too short, leaving the top edge flush with or just above the soil surface. Cutworms can easily climb over a barrier that is less than 2 inches tall, rendering the collar useless. Always measure the height after installation and adjust if needed.
Another mistake is failing to bury the bottom edge sufficiently. If the collar sits entirely above ground, larvae can tunnel underneath and reach the stem from below. Aim for at least 1 inch of burial, and firm the soil around the base to eliminate gaps.
Using materials that degrade too quickly, such as thin newspaper, leads to premature collapse. While newspaper is readily available, it often disintegrates within a few days under moist conditions, leaving the stem exposed. Opt for corrugated cardboard or plastic for longer durability.
Some gardeners place the collar too tightly around the stem, causing constriction as the plant grows. This can stunt development or create a wound that invites disease. Leave a small gap—about ¼ inch—between the collar and the stem to allow for natural expansion.
Neglecting to check collars after heavy rain or irrigation is another oversight. Water can wash away soil, lowering the effective burial depth and creating a gap at the base. After each watering event, inspect the collar and add soil if the bottom edge has become exposed.
Finally, relying solely on collars without addressing habitat factors can lead to persistent cutworm pressure. Tall weeds, dense mulch, and plant debris provide daytime shelter for larvae. Combine collars with regular weeding and mulch management to reduce the overall population.
Pro Tips
Label each collar with the planting date using a waterproof marker. This simple habit helps you track how long the barrier has been in place and reminds you when to inspect or replace it as the seedlings mature.
If you have a large number of transplants, create a collar‑making station with a template cut from a piece of plywood. Trace the template onto cardboard, cut multiple strips at once, and assemble them in batches. This reduces preparation time and ensures uniform size.
For gardens with persistent cutworm problems, consider planting a trap crop of sunflowers or corn around the perimeter. Cutworms favor these plants, and you can monitor the trap crop for larvae, then destroy them before they migrate to your main beds.
Encourage natural predators by providing shelter for ground beetles and parasitic wasps. A small pile of stones or a piece of bark near the garden edge offers daytime refuge for these beneficial insects, which will hunt cutworm larvae at night.
When using plastic cups as collars, cut the bottom out and slit the side to allow easy sliding over the stem. The cup’s rigidity makes it resistant to moisture, and the smooth interior prevents larvae from gaining a foothold.
For an extra deterrent, sprinkle a thin line of diatomaceous earth around the base of each collar. The fine powder is abrasive to soft‑bodied larvae and can reduce the number that attempt to cross the barrier. Reapply after rain, as moisture neutralizes its effectiveness.
Finally, record your results in a garden journal. Note the date of transplant, collar type, weather conditions, and any observed damage. Over seasons, this data will reveal which materials and timings work best for your specific microclimate, allowing you to refine your approach.
Troubleshooting
If you notice seedlings wilting despite collars, check for stem damage above the collar. Some cutworm species will climb onto leaves and feed on foliage, causing water loss. In such cases, inspect the plants at night with a flashlight and hand‑pick any larvae you find.
When collars appear chewed or torn, the culprit may be larger pests like slugs or snails, which can gnaw through cardboard. Replace the damaged collar with a more resistant material, such as a plastic cup, and consider adding a copper tape barrier around the base to deter mollusks.
If the soil around the collar remains constantly soggy and the cardboard disintegrates within a week, switch to a water‑resistant option or improve drainage. Raising the bed slightly or incorporating coarse sand can reduce water retention and prolong the life of cardboard collars.
Sometimes, seedlings show no visible damage but fail to thrive. This can indicate root‑feeding pests like wireworms, which are not stopped by a stem collar. In such cases, examine the roots for tunnels or lesions and consider applying beneficial nematodes targeted at soil‑dwelling larvae.
If you find larvae inside the collar after a few days, it suggests the collar was not buried deeply enough or there was a gap at the seam. Re‑install the collar with at least 1 inch of burial and ensure the overlapping edges are securely fastened.
Lastly, if collar installation feels time‑consuming, enlist a helper or set up a simple assembly line: one person cuts strips, another forms cylinders, a third secures the seam, and a fourth places them over seedlings. This teamwork reduces the effort per plant and speeds up the process.
FAQ
How high should the collar be above the soil?
The top of the collar should extend at least 2 inches above the soil line. This height prevents most cutworm larvae from climbing over the barrier. If you notice larvae reaching the stem, increase the height to 2½ inches for added security.
Can I reuse the same collar for multiple seasons?
Cardboard collars are designed for one season; they break down with moisture and soil microbes. Plastic cup collars can be rinsed and reused for two to three growing seasons if they remain uncracked and free of chemical residues.
What if I don’t have cardboard or plastic cups?
Stiff paperboard from frozen food boxes, the inner tube of a paper towel roll, or even a cut‑down plastic bottle can work. The key is rigidity and a smooth interior that larvae cannot grip.
Do collars work on all types of seedlings?
Collars are effective on any tender‑stemmed transplant, including brassicas, nightshades, cucurbits, and leafy greens. Woody‑stemmed plants like established asparagus or rosemary rarely need them because their stems are too tough for cutworms to chew.
Should I remove the collar once the plant is established?
You can leave the collar in place; it will not harm the plant and will continue to offer protection against any late‑season larvae. Removing it is optional and may improve air circulation at the base if you prefer a cleaner look.
Closing
Protecting seedlings from cutworms does not require expensive chemicals or complicated routines. A simple collar, properly sized and installed, creates a physical barrier that stops the most damaging behavior of these nocturnal pests. By combining collars with good garden hygiene—removing weeds, managing mulch, and checking for damage—you keep losses low and maintain a steady, healthy stand of transplants.
The method is scalable, whether you are tending a few balcony pots or a large community garden. Materials are readily available, often recycled, and the time investment pays off in saved seedlings and earlier harvests. Remember to monitor the beds each morning during the vulnerable establishment period and replace any compromised collars promptly.
As the season progresses and plants develop stronger stems, the need for collars diminishes, but the habit of inspecting your garden at dawn remains valuable. It builds awareness of other potential issues, from nutrient deficiencies to early signs of disease, making you a more attentive gardener overall.
Take the first step this planting season: cut a strip, form a cylinder, slip it over each seedling, and watch your transplants thrive. Your efforts will reward you with fuller rows, healthier plants, and the satisfaction of knowing you have outsmarted a common garden foe with nothing more than a bit of cardboard and a watchful eye.
Related: Prevent damping off seedlings