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Best Buy 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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Our Best Buy composts for sowing seeds all grew great seedlings. Almost all the seed we sowed germinated and then grew on to make robust young plants. 

Best composts for sowing seeds

A great compost for sowing seeds should have a fine texture that will surround the seeds with everything they need: water to kick-start germination and help the plant to grow; air to help the plant to mature, and a small amount of nutrients to fuel growth once the seed has exhausted its own stored nutrients. All our Best Buy composts give seeds all they need for strong, healthy growth. 

Each year, we test a wide range of composts by sowing a large seed that is usually easy to grow, and a small, fine seed that will be a little more tricky to germinate. This year we chose sweetcorn 'Lark' as the large seed and petunia 'Express Rose' as the small seed, sowing 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. 

See how all the composts scored by looking at the full results table and see which were Don't Buy composts for sowing seeds. 

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Compost Our verdict Sweetcorn seeds Petunia seeds Score
Compost non-member logo

Superb sweetcorn seedlings

Peat content: 57%

This peat-based mix has 10% grit and horticultural sand as well as 33% green compost and coir. 

Almost all the sweetcorn seeds germinated and the seedlings were large and healthy. The petunias had a lower germination rate than those in other composts, but the seedlings were some of the strongest in the trial.  

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Compost non-member logo

Best peat-free on test

Peat content: 0%

This compost has done very well in our tests in recent years and is peat-free without incorporating green compost. It uses sterilised loam and horticultural sand in the mix, which seems to suit small seeds. 

The sweetcorn germination rate was marginally lower in this compost than others, but the seedlings were the largest and some of the strongest on test. The petunias germinated very well and grew quickly. 

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Compost non-member logo

Best for small seeds

Peat content: 70%

This compost produced the largest and most robust petunia seedlings - the best in the trial. The sweetcorn had a 90% germination rate and the seedlings were among the tallest and healthiest. 

The fine-textured peat and wood-fibre mix was a Best Buy for both sowing seeds and raising young plants last year. This time around, the fuchsias didn't flower as well in this compost as in our Best Buy composts for raising young plants, so didn't make the grade

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Compost non-member logo

Large petunia seedlings

Peat content: 58%

This compost is a mix of peat and green compost, derived from sources other than municipal green waste. It seems to be well suited to seeds, with a fine texture that allows seedlings roots to make good contact with the compost. 

All but a handful of the sweetcorn seeds germinated and grew quickly. Only average results were achieved for petunia germination, but the seedlings were large and robust and would have made good plants. 

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