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1 October 2020

How to choose the right compost

Choosing the right compost can seem confusing. Read our guide to find out how to pick a compost that will be perfect for your gardening jobs. 
Compost for seeds antirrhinum 443522
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Adele Dyer

The best compost will have the perfect balance of nutrients, a medium-crumbly texture and good structure, while the worst will be too fine and use far too much fertiliser. 

Use our expert advice to help you decide what compost you need for sowing seeds, raising young plants and growing in containers – and then check our ratings to ensure you don't end up taking home a dud.  

Head to our best composts to find out which product you should buy. 

What are the different types of compost?

There are two main types of compost: multipurpose and composts for specific use, such as raising plants from seed or growing plants in patio containers.

Multipurpose and all-purpose composts 

  • Claimed to be suitable for germinating seeds, small seedlings and plants in patio containers, so there's no need to buy different types of compost for different stages in a plant’s life. 
  • Multipurpose composts are often cheaper than specific-use composts. 

Specific seed and potting composts 

  • Formulated to optimise plant growth by providing the right amount of nutrients to suit the plant at a particular stage in its life. 
  • They often contain additional ingredients to multipurpose composts, such as grit to aid drainage. 
  • Specific-use composts tend to be more expensive than multipurpose composts, but plants raised in these don't always grow any better, or even as well.

Here's our best composts for seed sowing and raising young plants.

Container composts

  • Container composts are formulated to optimise plant growth by providing the right amount of nutrients for plants in containers. 
  • Some contain a controlled-release feed and/or water-storing granules. 
  • Container composts tend to be more expensive than multipurpose composts.

Here's our best composts for containers.  

How much do I need to pay for a good compost?

Compost can be as little as 99p and as much as £15, it all just depends on the type and how many litres of compost you get in the bag. It's important to remember that a high price doesn't guarantee quality, though.

In fact, our testing shows really variable results for both cheap and expensive compost. The only way to really know what you're getting is to look at our results. 

Here's our best compost.  

Things to look for when buying compost

It's hard to know if a compost is good or bad just by looking at the packaging, but there are a few things to look out for: 

  • Good structure and aeration - whether you buy multipurpose or specific-use compost, this is important for encouraging strong root development and healthy plants.  
  • A medium-crumbly texture - is ideal. Composts that are too fine are prone to water logging, while those that are too coarse tend to need more frequent watering.
  • The right balance of nutrients - a good seed or potting compost should have the right balance of nutrients to grow a range of plants during this stage of their development, whereas a multipurpose compost should be able to support plants at all growth stages.

And remember: 

  • Quality isn't guaranteed - our compost trials have repeatedly found dramatic differences in how well plants grow in composts from different bags of the same brand.
  • Growing bags don't compare - traditionally, growing bags have been a low-cost way to buy compost. They have a reputation for containing cheaper-grade ingredients of inferior quality, and although we have found some good-quality bags in the past, this was not the case this year. 
  • Watch out for reformulated compost - one problem we face every year is manufacturers changing their composts after our tests are completed. We can't recommend reformulated brands because there's no guarantee that the new product will perform similarly. It's possible to find reformulated and old compost being sold at the same time, so our advice is to steer clear of buying compost in faded bags and, if possible, shop somewhere that has a high turnover of stock.

Keep your plants fed with one of our best controlled-release fertilisers

Is it true that I can catch Legionnaires' disease from compost?

The bacterium responsible for the potentially fatal Legionnaires’ disease has been found in many composts sold in the UK. The chances of you becoming infected are very low, but it makes sense to take the following precautions when handling compost:

  • Use compost in a well-ventilated place; keep the greenhouse or potting shed door open and avoid breathing in dust.
  • Wear gloves (and no smoking or snacking!) and wash your hands after use.

Want to go peat-free? Here's our guide on everything you need to know about peat-free compost

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