How Much Compost to Mix with Soil


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When it comes to getting the right ratios in the garden, you might be wondering how you work out how much compost you should mix with your soil.

It’s important to get the balance right because this saves you money and ensures your plants are healthy, but how do you know how much compost to use?

The quantity of compost you need depends on the type of plant you are adding it to, but in general, you want to add between half and a quarter of an inch of compost if you are putting the compost on top of the soil. If you are digging the compost in, you can dig about one to two inches in.

How Much Compost Should I Mix with My Soil?

Some plants are much hungrier than others, and if you are dealing with vegetables like tomatoes, eggplants, squash, melons, etc., you may want to mix in manure or compost in greater quantities.

In general, however, you can add about half an inch if you are putting the compost on the surface of the soil.

Did You Know: You may be able to find a compost calculator online. This should help you work out exactly how much you need.

How Much Compost Should I Use in Raised Beds?

How Much Compost Should I Use in Raised Beds?
Perfect amount of compost

If you are building raised beds, you might want different compost quantities.

A couple of inches of good quality compost, mixed with the soil, should be sufficient to make sure your plants grow well.

If you are growing vegetables in your raised beds, slightly increase the quantity of compost that you include.

How Much Compost Should I Use in a Pot?

You will usually want a maximum of thirty percent of compost in any container.

This should be sufficient even for heavy feeders, especially if you are also applying plant food on a regular basis. Don’t add more than this, because too much compost can burn the roots of plants.

Seedlings in particular are sensitive to being planted in too much compost and will struggle if you grow them in pots with an imbalanced growing medium.

Avoid Common Mistake: Make sure you are very careful with the ratios for young plants!

How Much Compost Should I Use on a Lawn?

How Much Compost Should I Use on a Lawn?
Apply compost to the lawn

Sometimes, you want to increase the nutrients available to your lawn.

This is usually over a much larger area, but it’s important not to add too much compost. Again, large quantities could burn the grass, and will add a thick layer that is hard for the grass to grow through.

Depending on when you last fed your grass, you should apply up to half an inch of compost evenly across the top of the lawn.

If you are trying to fill in bare patches, go up to half an inch deep and rake it over the soil.

How Much Compost Should I Use on My Garden?

If you are just adding compost to your garden in general, boosting the nutrients available to your plants and flowers, you should add between an inch and two inches of compost, and then dig this into the soil.

Ideally, you should aim to dig it to about six to eight inches below the soil’s surface, as most plants’ roots grow downward, so this is the best way to ensure that the nutrients are available to them.

Although you can use compost as a mulch on top, you may want to decrease the quantity.

The nutrients will wash down into the soil over time, but you don’t want to add so much that the compost burns the stems of the plants.

How Much Compost Should I Put Around Shrubs?

How Much Compost Should I Put Around Shrubs?
Compost around shrubs

If you are planting a new shrub, you should mix together about twenty-five percent in compost and seventy-five percent in normal soil.

This will give the plant sufficient quantities to grow with, but not so much that it suffers from too much food.

Depending on the kind of tree or shrub, you may want to add plant food a few months later, but the compost should sustain the plant for quite a while.

How Do I Add Compost to My Garden?

Many experts suggest that, if possible, you should spread compost on top of the soil, rather than digging it in.

You can mix the soil in if you are planting into a pot or filling raised beds, but if you are just improving the soil, you can spread the compost on the top.

This is considered better for the garden because digging disturbs the soil. There is a network of fungi called mycorrhizal fungi, and this helps plants access the nutrients that are deep in the soil.

When you dig, you disrupt the delicate strands of the fungi and reduce your plants’ ability to access these nutrients.

However, if you need to improve the structure of the soil, it is usually best to dig the compost in, because it will help with both aeration and moisture retention.

Remember This: Both clay soils and sandy soils are made better by digging the compost in and mixing it with the soil where you can.

When Should I Add Compost to My Garden?

When Should I Add Compost to My Garden?
Adding compost to your garden

You should add compost to your garden in small quantities in spring, giving your plants a gentle boost as they begin to enter the growth period.

About half an inch should be sufficient in most cases. In fall and winter, because the plants are not growing as much, you can add slightly more compost.

This will slowly break down and spread throughout the soil during the winter, increasing the nutrients without overwhelming the plants.


You rarely want to have a ratio of greater than thirty percent when it comes to including compost in your soil. For heavy feeders, use twenty-five or thirty percent, but reduce this for light feeders and seedlings.

Too much food can burn a plant’s roots and make it wilt, so be careful.

If possible, avoid mixing compost into your soil, and instead just spread it on top unless you need the structural improvement that compost provides.

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