Garden Basics

What Is The Best Ratio Of Compost To Soil?

Adding compost to your garden soil acts as an organic soil conditioner and amends the soil structure by adding the required nutrients for optimal growth.

Different types of soil require different amounts of added compost, but all soils will benefit.

Soil Type


Add Compost

Clay Soil

Compacts easily and needs compost to improve structure and drainage

3-4 inches (7.5-10cm)

Sandy Soil

Dries out quickly and benefits from compost to help retain moisture

3-4 inches (7.5-10cm)

Loam Soil

Loam soil has adequate soil structue

1 inch (2.5cm)

Types Of Compost 

  1. Homemade compost made from compost ingredients from kitchen and garden waste - carbon and nitrogen. This organic compost is easy to make and often has the added benefit of worm castings.
  2. Mushroom compost is made from used compost from mushroom growers and is a slow-release organic compost and a great soil amendment.
  3. Composted manure such as chicken, horse, or cow manure must be well decomposed and weed-free.
  4. Peat moss can be added to acid-loving plants such as rhododendrons and blueberries. Do a soil test to determine the pH of your soil. Use acidic pine needles or oak leaves as mulch.
  5. Green Manure. Growing a cover crop to improve the humus content of the soil. The crop is cut and left to decompose or dug into the soil.

Amend A New Garden Bed With Compost


Spread 3 to 4 inches (7.5-10cm) of compost and work it into the garden soil at a spade depth if it is heavy clay and sandy soil. 

Leave the bed for two weeks after tilling to allow the nutrients to become established in the disturbed soil. 

For loam soil, it is not necessary to dig it in.  

Compost For New Raised Beds


Always make sure that finished compost is free of weed seeds in raised garden beds.

Use a soil mixture of 30% finished compost to the other soil mixes, such as 60% topsoil or existing soil and 10% perlite/vermiculite.

After the first growing season, add 1 inch (2.5cm) of compost to the raised bed soil's surface. The compost does not have to be finished decomposing as the composting process will continue on the surface.

Adding Compost In Established Flower Beds

Add 1 inch (2.5cm) compost on the surface as a mulch so as not to disturb the roots of the established flower bed.

This compost addition will add to the plant growth over the next season.

Adding Compost To Soil For Container Gardens


Use equal parts of finished compost from the compost heap, vermiculite, and topsoil, garden soil, or bagged soil for container gardens. Bagged potting mix has an addition of peat moss, vermiculite, sand, bark, etc.

Different container plants require different mix of potting soil.  Try your hand at these DIY potting mixes.

Compost For New Lawns

Mix 1 part finished compost to 1 part topsoil to equal 2 to 3 inches (5-7.5cm) in depth.

Compost Applied As Top Dressing On Established Lawns

Sieve compost to fine particles. These particles will drop down amongst the blades of grass and encourage a lush green lawn.

Keep the top dressing to about a quarter inch in depth. Top dress the lawn regularly if there are bumps that require smoothing. 

Use grass clippings from regular mowings that can be left on the top as a regular topdressing. Mow the lawn without the grass catcher with regular mowing the grass clippings will add nutrients to the soil.

Compost For Established Trees and Shrubs

Add 1 to 2 inches (2.5 to 5cm) of compost  annually as a mulch to maintain healthy soil.

Compost For Newly Planted Trees

Dig a hole double the width and the same depth of the container.

Modern thinking is not to amend the soil, as amended soil encourages the tree roots to stay near the amended soil and not venture out into the native soil.

Backfill with the native soil after removing rocks and stones.

Apply mulch, which could be 1 inch (2.5cm) compost.

Water adequately until well established.

Compost For Newly Planted Shrubs

  • Dig the hole twice the depth and width of the container the plant came in.
  • Mix a third compost into the soil from the hole.
  • Add compost and soil mix into the hole positioned slightly higher than the soil line.
  • Backfill the rest of the compost soil mix.
  • Tap down with your foot.
  • Mulch with organic matter to improve soil health.
  • Water well and keep adequately watered until it is well established.

Can You Add Too Much Compost To Soil?

Compost that has matured will be beneficial for the growth of healthy plants. Unfinished compost should not be mixed into the soil until it has matured.

However, use unfinished compost as a mulch for trees and shrubs and in your veggie garden, and the worms will help with the decomposition.

Can Plants Be Grown In Compost Only?

Butternut, pumpkin, and squash sometimes grow directly out of the organic material in my compost pile or compost bin.

I add most of my spent potting soil from my annuals into my compost, which probably contributes to the added plant nutrients and minerals a growing plant needs.

But compost on its own is a soil amendment and conditioner and not a planting medium.

If using compost as a mulch in your garden bed or vegetable garden, then plant seeds and transplants directly in this mulch. The plant roots will develop deeper into the garden bed soil.

However, planting into compost alone as in a container or raised garden bed would not be advisable.

Best ratio of compost to soil.1


Different types of soil require different amounts of added compost, but all soils will benefit.

Unfinished compost should not be mixed into the soil until it has matured.

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