What Is Compost & How Do You Use It?

Updated February 28, 2022
tipping compost in wheelbarrow

There is almost a 100% chance that in any given article, book, or television show about gardening, compost will be mentioned and recommended. And there's a good reason for that: compost is magical. Truly. Not only does the process of composting allow you to recycle things normally destined for the trash, but the end product can improve garden soil, add fertilization, be used as mulch, and help retain soil moisture. See? Magic.

What Is Compost, Exactly?

Compost happens regularly in nature, all the time. Think of a forest: leaves fall every year, as do fruits, branches, and even entire trees. Animals die and fall to the forest floor as well. Over time, all of that decomposes thanks to insects, bacteria, and the effects of weather. What's left is a nutrient-rich substance that keeps the forest growing healthy year after year.

That's all compost is: decomposed plant matter. Gardeners can speed up and somewhat control the process by making their own compost, and it's absolutely worth doing. By adding lawn clippings, plant prunings, leaves, twigs, vegetable scraps, coffee grounds and other home and garden waste to a bin or pile, you can turn all of that "trash" into compost and then add it to your garden, containers, or lawn to improve soil health and retain moisture, while adding those nutrients right where they're needed most.

What Can You Add to Compost?

Composting can be as straightforward or as detailed and complex as you want it to be. Some gardeners simply heap up all of their grass clippings, prunings, leaves, and kitchen scraps and give it a turn every once in a while. Others carefully alternate layers of carbon-rich and nitrogen-rich ingredients in their compost bin to get the optimum mix for fast compost.

Either way, there are some tips about what you should and shouldn't add to compost piles.

Items to Add to Compost Piles

adding vegetable scraps to compost

You'll want to avoid adding things that will be smelly, attract pests, or make the compost harmful in any way (via disease or noxious weeds). You can definitely add:

  • Kitchen scraps, including egg shells, vegetable and fruit peels, apple cores, etc.
  • Leaves
  • Grass clippings
  • Small twigs
  • Weeds that you've pulled from the garden
  • Flowers that you've deadheaded or pinched off of your plants
  • Manure from chickens, hamsters, rabbits, gerbils
  • Coffee grounds
  • Tea bags
  • Sawdust or wood shavings
  • Black and white newspaper (shredded)

What Not to Add to Compost Piles

There are also a few things you definitely want to avoid adding. These items can encourage harmful bacteria, spread problem plants, or attract pests.

  • Animal bones/meat/fat
  • Dairy
  • Noxious weeds
  • Cat or dog waste
  • Diseased plants

You can make or build a compost bin, or you might want to consider a compost tumbler. When deciding how to compost, you'll want to take your space and how much compost you plan to make into consideration to find the method and container type that works best for you.

No matter which method you use, you'll want to turn the pile regularly. This moves unfinished compost to the center of the pile, and also adds oxygen, which helps the contents of the pile decompose faster.

How to Tell if Your Homemade Compost Is Finished

If you're not familiar with making and using compost, it's easy to be unsure about whether your compost is actually "done," and ready to be used yet or not.

Finished compost should have a rich, earthy scent. You shouldn't see any recognizable food scraps or remnants of what went into the compost pile, since those can cause pest and disease issues if you add them to your garden.

The most failsafe way to be sure your compost is fully finished is to put a scoop or two of compost into a plastic zipper bag or other plastic container that has a tight-fitting lid. Close it up and set it aside for two to three days. Then open it up and give the contents a sniff --if you pick up an ammonia or putrid scent, the contents aren't finished decomposing. Give the pile a turn and give it some more time.

Finished compost will smell good and be dark in color, with a crumbly, light texture.

Eight Ways to Use Compost in Your Garden

adding compost to garden

Now that you have a batch of finished compost, what can you do with it? Honestly, the question is what can't you do with it? There's a reason gardeners are obsessed with this stuff, and you'll soon see why they make all the compost they possibly can.

Amend the Soil in New Planting Beds

If you're starting a new flower garden or vegetable bed, adding compost will improve the fertility, texture, and water-retention of the existing soil. Add an inch or two of finished compost to the top of the bed, and then use a shovel or garden fork to work it into the top few inches of soil before planting.

Add it to the Vegetable Garden

Vegetable gardens, which need more fertility and moisture than most other types of gardens, really benefit from the addition of compost. You can either topdress and mix in the compost before planting, or, if you already have some things planted in the bed, you can simply topdress the entire bed, or add a bit of compost to each planting hole if you're putting in transplants.

Spread Compost Over Your Lawn

Compost is also great for the lawn. You can use a traditional lawn spreader (the kind you would use to spread seed or fertilizer) and spread the compost over your lawn. Or, if you don't have one, you can simply add shovelfuls to your lawn and then rake it, so that it falls to the surface of the soil. Do this in spring and fall (or even one or the other), and your lawn will need less water and look healthier over time.

Add Finished Compost to Potting Soil

If you enjoy container gardening, compost is a perfect addition to your planting containers. If you're planting a new container, simply mix compost into the soil you plan on using (up to 50% of it can be compost, if you want to use that much, but even a small amount is good!)

Or, if your containers are already planted, you can add a layer of compost to the top of the soil. When you water, the nutrients will work their way into the soil. You can do this a few times during the growing season, and your plants will love you for it.

Add Compost to Planting Holes

Whether you're planting perennials, annuals, shrubs, vegetables, or spring or summer-blooming bulbs, adding a bit of compost to the planting hole will help whatever your planting have a strong start. Trees are a bit different (and those are the next item in this list).

Topdress Around Newly-Planted Trees

The only case where you won't just want to add compost to the planting hole is when you're planting trees. You want tree roots to extend out into the native soil in search of moisture and nutrients, so if you just amend the soil in the planting hole, they're less likely to do that, instead confining themselves to that small area.

To counteract this, it's a good idea to topdress the soil around the tree, adding one to two inches of compost in an area that extends out to the ends of the branches forming the tree's canopy. The nutrients will wash into the soil when it rains or when you water, and the tree's roots will grow out in search of those nutrients.

Topdress Existing Beds

Any bed can benefit from the addition of compost. Existing beds, whether they're perennial gardens, annual beds, shrub borders, or mixed beds, are good candidates for a topdressing of compost. Add one to two inches (or really, as much as you have available) to the top of the bed and then rake it smooth.

Make Compost Tea

Compost tea is fairly straightforward to make it and is a wonderful organic fertilizer and foliar feed for your plants. You can use it anywhere in your garden or in your containers to give your plants a little extra nutrition while you water.

The best way to make compost tea is to use a pump or aerator to keep the water moving while it brews. However, if you don't have one, just make sure your brewing container is in an area where you'll see it several times per day. When you do, give the contents a stir to add more oxygen to the mix. Anaerobic compost tea will start to smell and will contain potentially harmful bacteria. So the safest way to make it, unless you're absolutely sure you'll take the time to regularly stir, is to buy an aerator to help with the process.

Compost: A Must for Your Garden

Whether you make your own compost or buy it from a local source, compost is definitely something you'll want to add to your garden. Your plants will be healthier, and your soil will improve with each addition of compost. Not too shabby for a bunch of decomposed plant matter!

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