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4 February 2021

Best composts for sowing seeds

Seeds are self-contained packages that have everything inside them to germinate and start to grow. They just need fine, well-drained compost.
Adele Dyer

A great compost for sowing seeds should have a fine texture that will surround the seeds with everything they need for strong, healthy growth. 

It should also have the right balance of nutrients to grow a range of plants at this early stage of their development. The worst however, will be prone to water logs and will be full of lumps. 

Make sure your seeds get off to the best start and avoid growing lack-lustre plants and veg by checking out the full table of results below. 

Best composts for sowing seeds

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Compost Our verdict Basil seeds Petunia seeds Score
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Best peat-free compost

Peat content: 0%

Price: £8.99 for 50L

Price per litre: 18p

This compost has often done well in our tests. The base mix of composted bark and wood fibre with a little coir has remained unchanged for some years, and this version has a small amount of sterilised loam and sand added. This makes it very open and freedraining, and perfect for developing seedlings. Although germination was slightly lower than the best composts for the petunias, both the petunia and basil seedlings were among the healthiest.

Where to buy: Garden centres. 
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Widely available peat-free

Peat content: 0%

Price: £6.99 for 50L

Price per litre: 14p

This compost has been altered significantly over the past few years and is now made from a treated wood fibre that creates a very open structure, and coir. The compost doesn’t contain green waste. The open structure meant both seeds germinated very well, but use one of our Best Buys composts for young plants for growing on your seedlings as it performs poorly for that use since it has low levels of nitrogen. .

Where to buy: Garden centres.
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A great all-rounder 

Peat content: 80%

Price: £14.99 for 70L

Price per litre: 21p

This mix of peat and wood fibre is fine, well-drained and yet moisture retentive, making it suitable for both sowing seeds and growing on young plants. The fertiliser isn’t mixed into the compost, but comes in a separate pack of controlled-release granules. We sowed our seeds without adding the fertiliser and both seeds germinated and grew away well. The petunia seedlings stood out as the best in this test, with high germination and strong growth.

Where to buy: Online
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Very high peat content

Peat content: 100%

Price: £5.50 for 60L

Price per litre: 9p

This is a traditional seed-sowing compost, made from just peat harvested in Ireland, and a base fertiliser that should last four to six weeks. Peat is well known to be a great medium for seeds and so it’s unsurprising to find that seeds germinate and grow on well in this compost. However, peat extraction has a negative ecological and environmental impact, so we have only included this compost in the seed-sowing trial as you can sow many seeds in small quantities of compost

Where to buy: Garden centres. 

Not found the right product for you? Browse all our compost reviews

Things to look for when buying compost for sowing seeds

Here are two useful features to look for when buying your compost:

  • Balanced nutrients - the right amount of different ingredients to grow a range of plants at this early stage of development.
  • Good structure - will encourage strong root growth.  

For more advice on choosing the best compost for you, head to our compost buying guide.

Getting the best from compost

It’s best to buy only the amount of compost you need, and use it up as soon as possible. This is particularly true of peat, which ideally should be used sparingly as it's bad for the environment. If you need to store any compost for more than a month, put it in the shed where it will be cool and dry, or undercover, especially through wet weather. If you can’t use up peat-free compost within three months of buying it, use it as a mulch on your borders.

Why Which? compost reviews are better

Which? is independent and doesn't accept advertising or freebies, so you can trust our reviews to give you the full, honest and impartial truth about a product.

Before testing we send out secret shoppers to buy all our compost so we know we are getting the same product as you. 

We then sow seeds of basil 'Cinnamon' and Petunia 'Express Rose', with 25 seeds of each in three half-size trays. 

When the majority of seedlings are at the first two true-leaf stage, we count the number of seeds that have germinated and rate the seedlings for size and vigour. 

To find out more, head to how we test compost. Alternatively, browse all our compost reviews.

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