Which? reveals the best composts for containersTests reveal a third of composts are Don't Buys

19 March 2015

Growing flowers

We grew almost 1,000 Sunpatiens 'Spreading Corona' to find our Best Buy composts for containers

Which? Gardening’s compost tests have shown that a good compost is hard to find. Out of the 27 composts for containers tested, only three were Best Buys, while nine, a third of the total, were Don’t Buys.

We know from years of testing that colourful bags and big name brands do not guarantee a good compost, nor does a high price tag. You can’t open the bags to look at the compost in the garden centre and even if you did you would have no idea whether it would grow good plants. 

Every year Which? Gardening tests a wide range of composts and last summer we grew almost 1300 plants for four months, choosing bedding plants and vegetables that we know our members enjoy growing in pots and hanging baskets. This year we found many of the composts failed to grow healthy plants and produced very disappointing displays, although we had three Best Buy composts for container plants. 

Nine Don't Buy composts for container plants 2015

Many of the Don’t Buy composts for container plants contain fertilisers that were meant to last the summer, but we found them to give poor, weak plants that struggled to grow and flower, and looked very unattractive. Some had pale green, yellow or even purple leaves, and the stems were straggly with few leaves, while our Best Buy plants were lush, dark green mounds of foliage, covered in flowers. 

Our expert advised this was because the composts didn't release enough nutrients, leaving the plants starved. He told us that claims of compost that have enough feed to last all summer are ambitious, given so many factors can effect a plant's growth, such as the temperature, how much it is watered or how much rainfall the pot is receiving, and where the pot is, such as on a sun-trap patio, a greenhouse or in a shady corner.

 Log on to find out which brands were Don't Buys. 

Peat-free Best Buys composts for container plants 2015

We were very pleased that among the Best Buys were two peat-free composts. This is good news for everyone worried by the ecological and environmental damage caused by peat extraction. Peat is due to be phased out of composts for home users over the next few years, but reliable peat-free composts have been hard to find.

The third Best Buy also came out top in Which’s sowing seeds and raising young plants tests, so is a good all-round buy.

To make sure you have stunning pots of plants covered in flowers to brighten up your patio, or a bumper crop of veg, look at our Best Buy composts for containers and check out our full results table. 

More on this.... 

  • Discover our Don't Buy composts for containers
  • Try our Best Buy composts for containers
  • Learn how we test compost