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Best Buy composts for raising young plants

By Adele Dyer

Seedlings and small plug plants need a compost that's low in nutrients to start with, but it should be able to keep the plants well fed as they grow.

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Our Best Buy composts for young plants consistently gave seedlings and plug plants the right conditions to put on impressive growth. 

Best composts for raising young plants for 2019

Young plants, such as seedlings and plug plants, need a compost with enough fertiliser to let them grow well, but not so much that it burns their roots. It also needs to retain enough water, while not drowning young plants in soggy compost. 

See how all the composts scored by looking at the full results table. 

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Compost Our verdict Young cabbage plants Young antirrhinum plants Score
Compost non-member logo
96%

Great all-rounder

Peat content: 80%

This peat-based compost has done very well in our tests for the past three years. It's mixed with 20% wood fibre. 

The young plants were particularly good, and those we didn't liquid feed grew strongly to the end of the test. 

A 100g bag of controlled-release fertiliser is included, which we mixed into the compost for the young-plants test, but not the seed test. 

It's only available online and delivery is extra. 

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Compost non-member logo
89%

Large young cabbage plants

Peat content: 50%

This has less peat than many we have seen this year and is mixed with wood fibre, which is free-draining and works well in peat mixes.

The cabbage seedlings romped away as soon as they were potted into this compost and were some of the largest plants in the test. the antirrhinums also grew well and were covered in flowers. 

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Compost non-member logo
88%

Fantastic antirrhinums

Peat content: 60%

This has a lower proportion of peat than many peat-based composts we have tested this year. the manufacturer doesn't tell us what else the compost contains, although we know that it has its own process for producing wood fibre and doesn't use any green waste. 

The cabbages were a good size and healthy, but the stars were the antirrhinums. These were among the largest in the test and covered in flowers.  

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How we test compost for raising young plants

We grew cabbage 'Caraflex' seedlings from the two true-leaf stage, and Antirrhinum 'White Appeal', bought as plug plants from a specialist nursery. After six weeks, we judged both the young plants on how vigorous they were, which includes looking at size, leaf colour, and whether the plants are stocky and strong or long and straggly. We also noted how well the antirrhinums were flowering. 

Don't Buy composts for raising young plants 2019

None of these composts grew good young plants. We think you should avoid them. 

Compost Our verdict Young cabbage plants Young antirrhinum plants Score
Compost non-member logo
38%

Lumps of woody material

Peat content: 0%

This is a mix of 80% composted bark fines and 20% green waste, which is garden waste that has been composted. Unfortunately quality control seems not to have been tough enough in this compost that we bought in spring 2018. It was full of large lumps of wood. 

Neither the antirrhinums nor the cabbages grew well - both were among the smallest in the test. 

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Compost non-member logo
33%

Poor nutrient balance

Peat content: 0%

This peat-free compost is clearly made from green waste, and was lumpy, woody and unworkable. The nutrients were imbalanced, with very little nitrogen but staggeringly high amounts of sulphates and phosphates, which make it acidic. 

The cabbages were tiny, pale-leaved and struggled to survive, and the antirrhinums were also small and had just a tenth of the flowers of our Best Buy composts.

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