Are Grubs Bad for Compost?

In most home compost piles, the stench of decay will attract flies and other insects that will eventually give way to grubs. Grubs in compost are very common and will accumulate anywhere there is abundant food and organic matter. The organic materials in our compost heaps can quickly become the home of thousands of wriggly crawling grubs.

While your initial reaction to a compost pile that is literally crawling with grubs may be disgust, like all natural processes, it is not a simple matter of whether grubs in the compost are good or bad. To find out if the grubs in your compost need to be gotten rid of or for more information on why grubs like the composting process, read on below.

Is It Good or Bad to Have Grubs in My Compost?

There are many kinds of grubs, white grubs, gray grubs, big grubs, and small grubs that will feast on the organic matter in compost materials. In most cases, these grubs will be harmless if it is near the beginning of the composting process. Common types of grubs will feed on the large compost mix, like banana peels and garden waste, and reduce it to nice finished compost. 

Some grubs can be undesirable, and a balance of beneficial creatures and kitchen food scraps should be maintained, or else your compost may turn into a black gooey nutritionless glop. When adult flies and other pests gravitate to your compost pile in large numbers, it is a good idea to try to eliminate the grubs at the larval stage to prevent new generations of pests. 

While many smaller white grubs will mostly feed on compost ingredients and eat microbes in the soil, others will eat the roots of plants if they survive and made it into your vegetable garden. In backyard compost, it is a good idea to try and get all the grubs out of the compost matter before adding it to garden beds to prevent grub worms from eating your plant roots.

As the number of common grub pests increases in your compost, you may start to lose nutritional content, and your end compost will not give much nutrition to growing garden plants. The composting process can be done quickly with grub worms through grub composting, but the resulting mix is not as nutrient-dense as a slow compost with animal manure.

The grubs of harmful insects and beetles can also lead to problems if adult beetles and pests make it into your garden. 

Types of Grubs in Compost Piles

Knowing which grubs will help your compost through aeration and the eating of microorganisms vs. the larvae that will grow into destructive adult insects can help you achieve better compost with fewer garden pest problems. Most grubs that turn into pests can still be beneficial in the early stages, so consider natural methods of removal later in their life instead of acting immediately. Even good grubs can become a problem if too many show up, so check out grubs and what to do with them.

Grub TypeFeeds OnCompost Benefit
Japanese Beetle GrubLive plant material Turn compost and break up compaction
Chafer GrubsRoot systems Break down rotting vegetable waste
Black Soldier Fly LarvaePlant wasteAn extremely fast breakdown of organic waste and non-aggressive adult forms
Vine Weevil GrubAll plant matterCreate large air pockets and move throughout the pile at night 
Pepper Weevil GrubPepper and nightshade plantsBreaks down fibrous stalks and vegetable waste
Bumble Flower Beetle LarvaeManure and rotting woodProcesses raw manure quickly

Japanese Beetle Larvae

Small white grubs only about an inch long, these larvae are found in most compost piles around North America. While mostly harmless in the compost, if they are able to enter your garden bed, they can create problems and do physical damage to your plants. Adult Japanese beetles are very bad for gardens, and stopping larvae from entering the pupa stage can keep pest populations down. 

Chafer Grub

These large white grubs can be around 2 inches long and live in rotting vegetable material. The large size of these pests allows them to aerate large chunks of a compost pile and helps break down organic materials much quicker than only worms and other soil microbes. Chafer grubs can live in the soil for many years, and when they emerge as Chafer beetles, they can cause damage to plants and gardens.

Black Soldier Fly Larva 

A common compost helper is black soldier flies; they look like wasps and act like houseflies but do not bite or sting and are easy to catch and relocate. Their larvae feed on rotting kitchen food scraps, and they can grow very big quickly. BSFL are great because they march their gray bodies out of the pile before entering the pupa stage, ensuring they won’t be around in your finished compost. 

Vine Weevil Grub

First seen as tiny eggs, these grubs hatch into maggot-sized c-shaped grubs. If these grubs make it into your garden, they can climb into the plants and feed on the roots. If they survive to adulthood, the beetles will feed on the leaves of the plants and wreak your garden. 

Pepper Weevil Grub

These small grubs have tiny dark oval-shaped bodies and are not c-shaped like other grubs. Most people will encounter this pest in a pepper garden or in composted fruit and plant materials from pepper plants. Adults eat the leave and exterior of the plant, whereas grubs in the fruit eat the peppers from the inside and cause them to fall off the plant. Make sure to remove these from compost before using them in a vegetable garden, as nightshades are at risk too. 

Bumble Flower Beetle Larvae

As an adult, these are noisy fliers that zip around our yard and gardens eating fermenting tree sap and rotting materials. These small white grubs also go c-shaped when disturbed but do not eat the roots of living plants. Bumble flower beetle larvae only eat rotting manure and decaying plant material and will not hurt your garden plants. 

What Should I Do with Grubs in Compost?

If you stumble upon a compost tumbler or pile full of grubs, you may be taken aback at first and unsure what to do. Once you have identified whether the pests are harmless or dangerous for your heap, you can decide what you want to do with them. There are a few options, and each one will require different amounts of time, energy, and overall effort to make happen. 

If you have decided that the grubs are not going to hurt your compost and, even better, will help you build soil much quicker, you may opt to leave them alone. Leaving them alone consists of feeding them the right worm food scraps and keeping the compost at optimal moisture levels, as you would with worms and other compost microbes. 

If you want the grubs to eat the large compost material at the start of the decomposition process but do not want them around depleting nutrients and possibly affecting garden soil, you can change the compost’s chemical composition over a few weeks. Adding more brown material, lime, citrus, and other biodegradable materials can decrease the grub population through starvation and other effects of a hostile environment.

How to Remove Grubs from the Compost Pit?

If you choose to remove grubs from your compost, you will want to choose a method that is easiest, cheapest, and the least time-consuming for you. Removing grubs can be as easy as exposing them to sunlight or heating up the pile. Choosing the right process will help you get the most out of grubs without risking the health of future garden plots. 

Sift Compost

In most cases, when we are ready to use our compost in our garden beds, not all organic materials will be broken down. A sifter made of different-sized screens or mesh can be quickly assembled and used to separate the finished compost from the materials that are still breaking down. Finer compost can be used for potted plants and seedlings, whereas a course sift works better in a garden bed or as a lawn amendment. 

When sifting grubs out, toss shovels full or pour compost over the mesh and let the grubs collect. Make sure to shake the screens back and forth until all the compost has fallen through and only the grubs remain. Once you have the sifted compost in a separate container, you can add the grubs to a new compost pile or use them in many other ways.

Hot Compost

Most of the compost critters in home compost piles like temperatures between 70 and 100 degrees but a hot compost pile can reach heat much higher than that. When heating up compost, you will need the right amount of organic materials 3×3 ft of waste is a good start, and the correct ratio of carbon to nitrogen; 30:1. 

Once the temperatures rise above 100, it is likely the grubs will begin to die off, and any remaining will be mixed into the rest of the biodegradable waste in the pile. Some eggs and pupa stages may survive higher temperatures, but the top temps of 160 should be enough to kill almost any pest stage in your compost pile. 

Use Chickens or Wild Birds

When fly and maggot problems get out of control, there are some natural biological solutions that may be free or cost very little to execute. If you happen to have a compost pile and a chicken or two, then letting your hens lose on the pile can quickly reduce grub and larvae populations. Chickens are ferocious eaters and can clean up a grub infestation in a matter of hours. 

If you do not have access to chickens to clean up your compost, you can make use of wild birds in the area. Exposing maggots and grubs to the surface of your pile can be enough to attract their natural predators. If that doesn’t work, you can try using bird seed in the pile to attract them and then let them peck the grubs while they are there. 

Expose to Sunlight and Weather

The inside of a compost pile can become a safe microclimate for grubs and decomposers, but the external temperatures on the surface of your compost may fluctuate greatly. If you are in the middle of summer or approaching winter, you can use the temperatures outside to kill grubs and stop them from spreading. 

If you turn your pile and expose the grubs on a hot day to the light of the sun, they will dry out completely and greatly reduce the number of pests. Repeat this for several days until each turn reveals few or no new grubs. In cold weather, you can get the same results as the frigid temperatures cause grubs to die or go dormant. and fall out of the pile.

Beneficial Nematodes

Earth-friendly nematodes can be used to quickly and effectively eliminate even extremely large populations of harmful grubs. It can be hard to get sprays and chemicals deep into compost piles, and fears of the effects of insecticides on microorganisms are real. To get around these limitations, nematodes can be deployed. 

These microscopic critters grab onto grubs and eventually eat them in much the same way a colony of ants can pick apart larger animals. Nematodes will not harm worms and will naturally reduce their populations as their food sources, grubs, become scarcer. Nematodes are readily available online or at garden stores. 

Add Diatomaceous Earth/Lime

DE and lime will cause dehydration and harsh environments for grubs to survive in. With a large enough application, most of the grubs that directly contact these powders will quickly die. The remaining grubs that are deep enough not to be contacted may be exposed later when the pile is flipped. 

Over time, lime and DE will make the compost unsuited for grubs and insects to occupy, and you will be able to stop adding more additives. Once the grubs have gone, you should experience a pest-free compost until new decomposing materials are added due to the reduced scent of decay. 

Chemical Treatment

In extreme conditions, carbaryl and trichlorfon can be used to chemically kill grubs and larvae in your compost and soil. These chemicals should only be used if a large number of dangerous grubs will become adults and attack the plants in your garden. You may also choose to use this option if no other method has worked or is feasible for you. 

When adding the chemicals, make sure to wear gloves and avoid contact with skin or any inhalation. Apply it according to the instructions and keep the application centralized to where the largest population of grubs is. Re-treat your compost pile as needed until you have a grub-free garden soil amendment ready to use in your lawn.