Which? Gardening has tried 17 composts for sowing seeds and 15 for raising young plants, such as seedlings and plug plants.
We found some gave great germination rates and produced robust seedlings. But even some big-name composts grew weak, unhealthy plants that would struggle to give a good summer display.
Sustainable Best Buys
We have two Best Buy peat-free composts for sowing seeds and two Best Buys that are peat-based. Peat is well known by gardeners for being the best compost for sowing seeds. It naturally contains little fertiliser, and its texture makes it easy for seedlings to grow healthy roots and strong shoots. But peat harvesting causes environmental damage and releases large amounts of carbon dioxide into the atmosphere.
There have been attempts by government for over twenty years to stop the sale of peat, but we’re still waiting. Until a ban is in place Which? Gardening magazine wants let gardeners know that great alternatives are available.
There are also three new Best Buy composts for raising young plants, such as seedlings and plug plants. One of these is peat-free and it scores as highly as the two peat-based Best Buy composts.
Learn more about going peat-free in your garden.
Popular brands named as Don’t Buy composts
At the other end of the scale we found two Don’t Buy composts for raising young plants, one of which is one of the most widely-available peat-free composts, and the other is John Innes Young Plant compost from one of the largest compost manufacturers.
John Innes used to be a name that gardeners trusted to contain great compost. Our tests have shown that all too often it’s now far poorer quality than multipurpose composts. This is largely down to poor ingredients being used in the compost, often making it hard for water to drain from the compost. As a result seedlings struggle to grow.
Discover how to choose the right type of compost for your needs
How Which? tests compost
Which? Gardening has tested compost every year for over 30 years. We know how important a good compost is to successful gardening, and that premium or big-name composts don’t always give good value for money.
We choose composts that are widely available, and we include as many peat-free brands as possible. We grow two varieties of seeds, and two of young plants to make sure our composts are good for plants that need different conditions to grow well.
It’s also important that composts are consistently good, as quality can vary from batch to batch. So we buy four lots of each brand to make sure there are no dips in standard. This makes for a lots of pots. In total we grow 24 seeds trays, each containing 25 seeds, and 48 pots of young plants for each of our brands.
Find out more about how Which? tests compost