How to Use Compost Well

I’ve seen endless information about how to make compost but very little about what to do with it once it “happens.” One frequent question I get as a Master Gardener is when and how to use this garden black gold. I decided to write a comprehensive post about it.

Whether you put organic matter in a bin, a pile, or directly in your garden beds you can use the resulting compost in many ways.

Photo caption: My mom's commercial compost bin and aerator tool.

First, you need some compost. You can make it in a commercial bin, put it in a homemade bin, use a worm bin, compost directly in your garden beds, pile it in a lasagna garden, find some free compost,  or buy some compost (in bags or by truckload).

If you don’t know how to compost you can check out one of these resources to get started:

Fully decomposed compost should smell good (not sour or stale) and have no recognizable bits of debris left in it. In undisturbed piles you may need to dig to the bottom for the usable compost.

Photo Caption: Fully decomposed compost should smell good (not sour or stale) and have no recognizable bits of debris left in it. In undisturbed piles you may need to dig to the bottom for the usable compost. "Compost" sold at garden centers is often a lifeless pile of decomposed bark -- be wary what you pay for.

Once you have compost (a glorious state to be in) you get to use it.

The problem is, a lot of people don’t know how to do that. Sure, you put it in your garden or flower pots… but how much? When? How often? Is it a soil amendment or a fertilizer? Can you use it to start seedling trays?

As far as when to use it — anytime. But winter is often the most convenient since you don’t have to dodge dumping shovel loads on your plants when they are dormant.

  1. USING SCRAPS: If your main composting incentive is sustainably getting rid of a chunk of your garbage, deciding how to use your compost is pretty simple. You can just spread it anywhere in your yard that you’d like to make plants happy. You can even rake it lightly over lawns to improve the quality of your grass. If you don’t have anywhere to put it, give it to a grateful gardening friend.
  2. AS A BED AMENDMENT: More serious gardeners tend to start composting when they hear it will improve their beds. This can be disappointing if you’ve invested in one of those little commercial bins — you get your first load of finished compost, spread it in the garden, and when the weather heats up your compost vanishes. Most soils are so impoverished for humus that organisms use it up in a matter of weeks. I know how tempting it is to think, “I only have a small pile so I’ll spread it out over as much space as possible.” Don’t waste it! It’s better to put a thicker layer in a small area. If you really want to improve your soil you need a lot of compost. A whole lot. Rent a truck and pick it up somewhere if you have to! It’s hard to use too much and the more, the better. I’ve been known to spread it as thick as 8″ deep on new beds and I try to add at least 3″ more per year. If this seems like too much work to you, think of how many times you’ve gone out to plant new things and had to dig and amend a hole for each transplant or seed. Did you have to dig through rocks or clay? Did you mix in what seemed to be a lot of organic matter only to find the hole you dug was like concrete (and the plant suffering or dead) only months later? Surely it’s easier to amend the whole bed with a thick layer of compost once a year and have soil so friable that you can plant with your bare hands (I do). Do it in the winter when everything is dormant and summer heat doesn’t beat you down. If you can’t handle the labor, consider hiring someone to help or bribe your friends with a nice meal. Once you’ve put on that heavy blanket of compost it does take a season to really work itself in. Don’t step in it! Mark your beds with obvious walkways and stepping stones!
  3. AS FERTILIZER: Compost aerates soil and provides food for plants and useful organisms like earthworms. The humus retains water and helps soil form a crumbly texture, allowing nutrients to be taken up more readily by roots. It encourages symbiotic fungi that improve plant growth, buffers pH, and reduces erosion. If you use an organic fertilizer, the organisms that compost hosts will help break it down for your garden. These benefits lower stress and improve the immune system of your plants. It is a satisfying and practical way to recycle table scraps. But it isn’t a miracle fertilizer. The NPK value of compost varies depending on the ingredients you use (manure compost will rate higher in Nitrogen, etc.) but in general, compost from home scraps is estimated around 1-1-1. That doesn’t mean it doesn’t add to the fertility of your garden but if you want heavy production in food or flowers you should get a soil test (or test your compost itself) and add amendments to fertilize your soil. It’s important to realize that the amount of organic matter (compost)  in your soil will affect how well your plants take up food. For example, applying compost at the same time you use natural rock fertilizers encourages organisms that help release the nutrients so your plants can absorb them. (SEE BELOW FOR COMPOST INGREDIENT LIST).
  4. AS SEED STARTING MIX: Compost is alive with mostly good critters but indoors this can get off balance. Therefore, it is best to sterilize your compost before you use it for a seed starting medium. If you’re worried about earthworms you can spread the compost on a sheet in bright sunlight to get worms to leave your compost before you heat it up. My recipe calls for 1/3 compost to 2/3rd lightweight growing mediums like vermiculite. Sift the mixture to remove large particles that could block or smother seedlings. Some people use 100% compost but your seedlings may grow leggy if it is very rich. You should not need to fertilize until the seedlings grow a set of true leaves.
  5. IN POTS: You can make the above potting mix (without sifting) to plant or repot with. If you need to spruce up an existing container you should top it off with 1″ – 2″ of fresh compost twice a year. If you use slow-release fertilizer it is good to do it at the same time you add compost.
  6. AS MULCH: Compost is great at helping soil retain water but poor at repressing weeds. I tend to use unfinished compost for mulch because the larger pieces are more likely to smother weed seeds. You can also put down a wet layer of newspapers (3 – 5 sheets thick) underneath your mulch to block weeds. If you don’t have room for a compost pile, using your mulch as compost is a great time and space saving way to get organic matter to your beds each year. Just choose a biodegradable mulch — once it breaks down you can simply mulch over the top of it with a fresh layer. Layer it 3″ – 5″ thick and make sure it doesn’t rest against the trunks of trees or crowns of plants because it can cause them to rot.
  7. AS COMPOST TEA: I don’t use compost tea but I know many gardeners who swear by it. Here’s a photo tutorial on how to make it and an article on how to use it.

For those of you who would like to use your compost as a fertilizer you’ll need to use a composting formula high in NPK to get the best results. Here’s the NPK values of possible compost materials:

Values represent NPK: “Material Nitrogen”, “Phosphorus”, and “Potash” (K)

Use of a – means a zero value for that slot

  • Alfalfa hay 2.45 0.5 2.1
  • Apple fruit 0.05 0.02 0.1
  • Apple leaves 1 0.15 0.35
  • Apple pomace 0.2 0.02 0.15
  • Apple skin (ash) – 3.08 11.74
  • Banana skin (ash) – 3.25 41.76
  • Banana stalk (ash) – 2.34 49.4
  • Barley (grain) 1.75 0.75 0.5
  • Bat guano 6 9 –
  • Bean and pod 0.25 0.08 0.3
  • Beet waste 0.4 0.4 3
  • Beet waste (root) 0.25 0.1 0.5
  • Blood meal 15 1.3 0.7
  • Bone meal 4 21 0.2
  • Bone (ground and burned) – 34.7 –
  • Brewer’s grains (wet) 0.9 0.5 0.05
  • Brigham tea (ash) – – 5.94
  • Cantaloupe rind (ash) – 9.77 12.21
  • Castor bean pomace 5.5 2.25 1.13
  • Cattail reed & water lily 2.02 0.81 3.43
  • Cattail seed 0.98 0.39 1.71
  • Chicken manure 1.63 1.54 0.85
  • Coal ash (anthracite) – 0.125 0.125
  • Coal ash (bituminous) – 0.45 0.45
  • Cocoa shell dust 1.04 1.49 2.71
  • Coffee grounds 2.08 0.32 0.28
  • Coffee grounds (dried) 1.99 0.36 0.67
  • Corn (grain) 1.65 0.65 0.4
  • Corn (green forage) 0.3 0.13 0.33
  • Corncob (ground, charred) – – 2.01
  • Corncob (ash) – – 50
  • Cotton seed 3.15 1.25 1.15
  • Cottonseed meal 7 2.5 1.5
  • Cottonseed-hull (ash) – 8.7 23.93
  • Cotton waste 1.32 0.45 0.36
  • Cow manure (fresh) 0.29 0.17 0.1
  • Cowpea, green forage 0.45 0.12 0.45
  • Cowpea, seed 3.1 1 1.2
  • Crab (common) 1.95 3.6 0.2
  • Crab (king, dried and ground) 10 0.25 0.06
  • Crab (king, fresh) 2.3 – –
  • Crabgrass 0.66 0.19 0.71
  • Cucumber skin (ash) – 11.28 27.2
  • Dog manure (fresh) 1.97 9.95 0.3
  • Duck manure (fresh) 1.12 1.44 0.49
  • Egg 2.25 0.4 0.15
  • Eggshell (burned) – 0.43 0.29
  • Eggshell 1.19 0.38 0.14
  • Feather 15.3 – –
  • Felt hat factory waste 3.8 – 0.98
  • Field bean (seed) 4 1.2 1.3
  • Field bean (shell) 1.7 0.3 1.3
  • Fish scrap (red snapper) 7.76 13 0.38
  • Fish scrap (fresh) 6.5 3.75 –
  • Greasewood (ash) – – 12.61
  • Gluten feed 4.5 – –
  • Greensand – 1.5 5
  • Grape leaves 0.45 0.1 0.35
  • Grapes (fruit) 0.15 0.07 0.3
  • Grapefruit skin (ash) – 3.58 30.6
  • Hair 14 – –
  • Hare and rabbit waste 7 2.4 0.6
  • Hoof meal and horn dust 12.5 1.75 –
  • Horse manure (fresh) 0.44 0.17 0.35
  • Incinerator ash 0.24 5.15 2.33
  • Jellyfish (dried) 4.6 – –
  • Leather (acidulated) 7.5 – –
  • Leather (ground) 11 – –
  • Leather (ash) – 2.16 0.35
  • Lemon cull 0.15 0.06 0.26
  • Lemon skin – 6.3 31
  • Lobster (refuse) 4.5 3.5 –
  • Lobster (shell) 4.6 3.52 –
  • Milk 0.5 0.3 0.18
  • Mud (fresh water — dredging product) 1.37 0.26 0.22
  • Mud (harbor — dredging product) 0.99 0.77 0.05
  • Mussel 0.9 0.12 0.13
  • Mussel mud (dried) 0.72 0.35 –
  • Molasses residue (brewing) 0.7 – 5.32
  • Moss 0.6 0.1 0.55
  • Oak leaf 0.8 0.35 0.15
  • Oats grain 2 0.8 0.6
  • Olive pomace 1.15 0.78 1.26
  • Olive refuse 1.22 0.18 0.32
  • Orange cull 0.2 0.13 0.21
  • Orange skin (ash) – 2.9 27
  • Oyster shell 0.36 10.38 0.09
  • Paint processing waste 0.02 39.5 –
  • Pea pod (ash) – 1.79 9
  • Peach leaf 0.9 0.15 0.6
  • Peanut (seed & kernel) 3.6 0.7 4.5
  • Peanut shell 0.8 0.15 0.5
  • Peanut shell (ash) – 1.23 6.45
  • Pigeon manure (fresh) 4.19 2.24 1.41
  • Pig manure (fresh) 0.6 0.41 0.13
  • Pigweed (rough) 0.6 0.16 –
  • Pine needle 0.46 0.12 0.03
  • Potato (tuber) 0.35 0.15 0.5
  • Potato (leaf and stalk) 0.6 0.15 0.45
  • Potato skin (ash) – 5.18 27.5
  • Poudrette 1.46 3.68 0.48
  • Powderworks waste 2.5 – 17
  • Prune refuse 0.18 0.7 0.31
  • Pumpkin (fresh) 0.16 0.07 0.26
  • Pumpkin seed 0.87 0.5 0.45
  • Rabbit brush (ash) – – 13.04
  • Ragweed 0.76 0.26 –
  • Redtop hay 1.2 0.35 1
  • Rhubarb stem 0.1 0.04 0.35
  • Rockweed 1.9 0.25 3.68
  • Rose (flower) 0.3 0.1 0.4
  • Salt-marsh hay 1.1 0.25 0.75
  • Salt mud 0.4 – –
  • Sardine scrap 7.97 7.11 –
  • Seawood 1.68 0.75 4.93
  • Sheep manure (fresh) 0.55 0.31 0.15
  • Shoddy and felt 8 – –
  • Shrimp head (dried) 7.82 4.2 –
  • Shrimp waste 2.87 9.95 –
  • Silt waste 9.5 – –
  • Silk mill waste 8.37 1.14 0.12
  • Silk worm cocoon 9.42 1.82 1.08
  • Sludge 2 1.9 0.3
  • Sludge (activated) 5 3.25 0.6
  • Sludge from sewer beds 0.74 0.33 0.24
  • Soot from chimney flue 5.25 1.05 0.35
  • Starfish 1.8 0.2 0.25
  • Sunflower seed 2.25 1.25 0.79
  • Sugar (raw, residue) 1.14 8.33 –
  • Sweet potato skins (ash) – 3.29 13.89
  • Sweet potato 0.25 0.1 0.5
  • Tanbark (ash) – 0.34 3.8
  • Tanbark ash (spent) – 1.75 2
  • Tankage 6 5 –
  • Tea grounds 4.15 0.62 0.4
  • Tea leaves (ash) – 1.6 0.44
  • Timothy hay 1.25 0.55 1
  • Tobacco leaves 4 0.5 6
  • Tobacco stalk 3.7 0.65 4.5
  • Tobacco stem 2.5 0.9 7
  • Tomato fruit 0.2 0.07 0.35
  • Tomato leaves 0.35 0.1 0.4
  • Tomato stalk 0.35 0.1 0.5
  • Wheat, bran 2.65 2.9 1.6
  • Wheat grain 2 0.85 0.5
  • Wheat straw 0.5 0.15 0.6
  • White clover (green) 0.5 0.2 0.3
  • White sage (ash) – – 13.77
  • Wood ash (leached) – 1.25 2
  • Wood ash (unleached) – 1.5 7
  • Wool waste 5.5 3 2

*Note: I found the above list on at least 30 different websites. I’d love to credit the original source if someone has it.

If you’ve found additional ways to use compost please let me know!

Eliza Lord

I'm a Greenville, SC native (the Appalachian foothills) who wears the hats of Greenville Master Gardener & Upstate Master Naturalist. I love to write about food and sustainability.

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