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Best composts for sowing seeds

By Adele Dyer

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

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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. 

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Best composts for sowing seeds

Compost Our verdict Basil seeds Petunia seeds Score
Compost non-member logo
96%

Best quality seedlings

Peat content: 100%

This compost was a Best Buy for sowing seeds last year, too. It’s made from just peat with a base fertiliser, which was traditionally thought to be an ideal material for sowing seeds. However, as peat is a precious resource, we would urge you to consider only using this in small quantities. Germination was excellent for basil and exceptionally high for the petunia seeds, and the seedlings matured quickly into strong small plants, which lasted well before potting on.

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Compost non-member logo
92%

Excellent basil seedlings

Peat content: 80%

This compost has been a Best Buy for seeds every year since we first tested it in 2016. Mainly made from peat, but with around 20% wood fibre, it comes with a packet of controlled-release fertiliser, which we added when potting up in the compost for the young plants test. 

The basil seeds germinated particularly well, and while the germination rate for petunias wasn’t the best, both sets of seedlings grew well.

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Compost non-member logo
92%

High germination 

Peat content: 70%

This compost has been a Best Buy for seeds for the past two years. It has a high peat content, with a blend of rock dust, envii bacteria, vermiculite, zeolite infused with seaweed extracts, and base fertiliser. We’ve found this mix was great for seeds, but less so for young plants. 

More basil seeds germinated in it than in any other compost in the test, and both petunia and basil seedlings proved to be a good size as well.

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Compost non-member logo
90%

Great germination rate

Peat content: 100%

This is the first year we’ve tested this compost. We’ve tried to include them in previous tests but have been unable to find enough suppliers. This one has a very high peat content, so we would really only recommend it for sowing your seeds, and then choose a lower-peat compost when filling large pots. 

It grew particularly good basil seeds, which germinated and grew on very well. The petunia seedlings weren’t quite as good, but were still among the best on test. 

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The best peat-free composts for sowing seeds

This year, the best peat-free options for seed sowing are the two Melcourt SylvaGrow composts. Their scores show the germination was good and the seedlings were healthy, but weren’t quite as strong as our Best Buy composts.   

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

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 'Puck' and Petunia 'Express Rose', with 25 seeds of each in quarter-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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