Can Compost Kill Plants?

This article was reviewed by Steve Snedeker, professional landscaper.

Dying plant and composted soil held by gardenerComposting can be a rewarding experience. You get to recycle your kitchen scraps. You have the satisfaction of creating soil for your plants or yard or garden. Organic material is so good for your plants. Compost gives your plants an extra boost of nutrients. But sometimes, too much of anything might cause damage. We've learned that there are pros and cons to using compost. We got to wondering about the cons. Can compost kill plants?

The slow release of nutrients from compost helps grow healthy plants. But compost that is not matured correctly might harm or even kill your plants. And, using too much compost can smother and kill plants.

You might be thinking that compost is organic. How can compost harm or even kill your plants? We did the research. Keep reading as we explore the topic of compost in-depth and guide you on proper usage for your plants.

Can You Plant Directly Into Compost?

If compost is the only material you use for planting, you will likely create problems for adequate plant growth. The organic material, sometimes called "black gold," is rich in some nutrients, but not all. A compost only base might harm or kill your plant. Adding compost to your topsoil or mixing it with store-bought soil will enable you to create the ideal planting base. The combined materials will have the right mixture of nutrients and minerals that your plants need to flourish.

You've worked hard to create compost, so make sure you put it to good use and mix few inches into other dirt.

Can I Use Compost Instead Of Topsoil?

Compost and topsoil should be used together. Separately, these materials lack the ideal amount of nutrients for your plants. Over time, topsoil erodes and loses essential elements like nitrogen. Compost lacks some of the nutrients your planting soil needs to develop. You should add compost to your soil during planting seasons like spring or fall when you are tilling your dirt. The combination of the two materials creates a healthier soil for your plants to thrive in.

The University Extension of Missouri recommends that compost makes up 30 percent of the volume of soil you are using to plant with. The mixture of dirt can be added to your soil when planting trees, shrubs, or flowers into the ground. A thin layer of compost can also be added to the top of your grass. And if you are using containers for your plants, herbs, or vegetables, be sure to mix in the proper amount of compost to the soil.

How Do I Use Compost?

Compost inside wheel barrow and hauled by shovel

We've covered that compost shouldn't be used solo. For best results, a fully cured compost should be mixed with soil. There are several ways to incorporate compost into existing dirt.

Here are a few examples of adding compost to your soil:

Grass Yards

Once your compost is dark and crumbly, you can spread one to two inches of the material over grassy areas. Compost can also be used over your existing topsoil. Just be sure that you work it into the dirt with a rake or hoe.

Vegetable Gardens

Your in-ground garden can have a nutrient-packed planting bed by adding compost. It depends a bit on your growing season, but for most people, you should spread a few inches of compost over existing topsoil in the fall. When spring arrives, work the compost into the soil with a rake or hoe.

When it's time for you to plant, put a little compost in each hole you dig. As the plants grow, you can enhance the soil with small amounts of compost.

Plant Beds

Any annual or perennial plant bed can be improved with the addition of compost. Cover the area with about an inch of compost and work it into the soil. If you live in an area with frigid temperatures, a layer of compost added in the fall can help protect the roots from freezing. If you live in a warm or dry area, the layer of compost can improve drought resistance.

Potted plants

Just like the soil you use on the ground, the soil in your pots needs to be revived. Add about an inch of compost on top of the soil once or twice a year. And, if you are potting new plants, be sure to mix the right amount of compost into the soil.

Compost Is Food For Soil

We've established that compost is food for the soil. Working together, dirt and compost give your plants the right base of soil. Let's look closer at vegetables, perennials, and annuals.


Bonnie Plants is a popular grower of almost 300 plant varieties and available at most home or garden stores. Tomato, corn, and squash are a few examples of plants that require a lot of feeding energy and nutrient-filled soil. Even the best soil should be amended with compost when replanting.

Prepare the planting area by working a few inches of compost into the existing soil. Dig the holes for your vegetables and add a few handfuls of compost into the hole. If you're replanting into a pot, make sure to mix compost into the soil before planting.

Soil should also be fed compost throughout the growing season.


Seeing your plants return in the spring and summer can lift your spirits. So, it's essential to give your perennials' soil the right food.

When you're planning your garden with plants like Lady's Mantle, Hydrangeas, or Evergold, your soil needs to be healthy. For an established in-ground garden, you need to add an inch of compost material at least twice a year and work it into the soil. If you are creating a new garden or adding new plants, you might need two or three inches of compost tilled into the soil.

You should also be aware of your growing zone before you plant. Check out our post When to plant perennials (by zone and state) for detailed information on the best times to plant in your area.

For indoor or outdoor potted plants, amend the soil by adding compost in the spring and fall. You can also add a handful of compost throughout the year.


Annuals are amazing, growing from seed to plan in just one season. And even though most annuals will only last one season, they still need fertile soil to thrive. Like with the perennials, annuals need soil with the proper nutrients. Work a couple of inches of compost into topsoil in your garden beds. For your container plants, mix in about 30 percent of compost to the soil before you plant.

If you are looking for ideas on what type of annual to plant, read our post on 18 Full-Sun Annuals that Bloom All Summer.

Compost mixed into your soil will provide your vegetable and plant gardens the boost they need to be their best. Even your indoor houseplants need vibrant soil to grow. Keep your soil healthy with regular handful sized compost feedings.

Should You Buy Compost?

When it comes to compost, homemade is usually the best way to go. But it's not always possible, as you might not be able to create a space to compost in. Or, your compost might not be fully cured. There are many options for you to find a commercial compost supplier. Almost all local home and garden store will have bagged compost available for sale.

You can also visit The US Composting Council's site. They maintain a list of farms, companies, and organizations that have commercial compost available for sale by state. The Council also certifies the composting products.

Can Compost Be Dangerous To Pets Or People?

Compost can be dangerous to pets and people. The process of composting has four stages to complete before reaching maturity, where it's safe to use. During these stages, the pile of decomposing material will have bacteria and mold. Both of which are harmful to humans and animals.

Once the material has reached the full cure stage, it can be used with your plants in your soil. While the compost pile is breaking down, it should be covered or fenced off from animals and pets.

Composting Is Cool But Can Kill

Incorporating "black gold" or compost into your gardens and plants feeds the soil with a serious dose of nutrients. Composting is a cool way to recycle kitchen scraps and yard waste into soil.

But keep in mind, too much of a good thing can cause harm or even kill plants. To ensure your plants are not in harm's way, make sure the compost you use is fully matured. Your compost should be dark and crumbly with no evidence of any other materials.

Remember, you should always mix compost into existing soil or soil that you have purchased. Think of compost as the ultimate food your soil and feed it during spring and fall or as needed.

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