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Best composts for containers

By Adele Dyer

You need a great compost to grow pots of bedding and bumper crops of veg. Our tests find the best composts for pots and containers.

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The best compost for containers will help you grow large, healthy vegetables and plants that are covered in flowers all through summer. 

The worst we've tested will cost a fortune and only deliver slow growth, pale leaves and tiny harvests. 

But the only way to tell the good from the bad is to grow plants in the compost and compare the plants - which is exactly what Which? Gardening has been doing for more than 30 years. 

We've pulled out our top composts for containers from our tests in the table below. We also reveal the composts you're better off avoiding. 

Only logged-in Which? members can view our recommendations in the table below. If you're not yet a member, you can get instant access by joining Which?.

Best compost for containers

Compost Our verdict Pelargoniums Potatoes Score

Compost non-member logo

Peat content: 90%

M **** **** 72%

Good for flowers

This peat-based compost was almost a Best Buy in our compost for young plants test this year (Jan/Feb 19). It’s mostly peat, but also contains a small amount of green compost.

The pelargoniums were particularly robust. They were among the largest in the test from early summer and were some of the best-flowering plants with more than 80 flowers stalks over the summer.

There were plenty of good-quality potatoes, too, but most were small or medium in size.

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Compost for containers to avoid 

The worst compost for containers will leave you with diseased veg and plants with little to no flowers. Here are two composts that we wouldn't recommend buying: 

Compost Our verdict Pelargoniums Potatoes Score

Compost non-member logo

Peat content: 0%

M *** ** 43%

Nutrient poor

This mainly ‘green compost’ is made from green-waste bin collections and this year, it was very lumpy with large chunks of poorly milled wood.

Within weeks of being planted, the pelargoniums’ leaves were pale with a red tinge. The plants hardly grew in the crucial first weeks and didn’t recover later on, remaining small and flowering poorly. The potato yield was also very low.

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Compost non-member logo

Peat content: Not stated

M ** *** 40%

Needs supplementing

This peat-based compost has controlled-release feed added to the mix.

It has scored poorly in the past and this year the pelargoniums were clearly struggling to grow a few weeks after planting. We supplemented with a liquid feed after four months, but they continued to be small with few flowers and the potato crop was also low.

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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.

Here's a run through of how we test compost: 

  1. We grow 12 pots of pelargonium 'Designer Salmon' and 12 pots of potato 'Sarpo Axona'.
  2. We mix in a Best Buy controlled-release fertiliser, unless the compost bag stated that it contained enough feed to last for more than the four months that our trial lasted. In these cases, we assessed how well the plants were growing in July and started to liquid feed those that needed a boost, as suggested on the packaging.
  3. The pelargoniums were assessed for flowering impact and vigour, which means leaf colour, the size and bushiness of the plant and general health. We carried out these assessments three times through the summer in July, August and September. 
  4. The potatoes were harvested in September, when they were weighed and assessed for size and quality. 

Our scores are based on how well both trial plants did, weighting the results of both trials equally.

We test all types of compost - here's our round-ups of the best compost for raising young plants and the best compost for sowing seeds.

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