We use cookies to allow us and selected partners to improve your experience and our advertising. By continuing to browse you consent to our use of cookies. You can understand more and change your cookies preferences here.

Choose the right compost

By Adele Dyer

Put us to the test

Our Test Labs compare features and prices on a range of products. Try Which? to unlock our reviews. You'll instantly be able to compare our test scores, so you can make sure you don't get stuck with a Don't Buy.

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 tasks.

What are the different types of compost?

Our trials test several different types of compost, including multipurpose and those for a specific use, such as raising plants from seed or growing plants in patio containers.

Multipurpose and all-purpose composts 

These are 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. We have found that some multipurpose composts, especially peat-based composts, have done well across the board in our tests. 

Specific seed and potting composts 

These are 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.

Find out which are our Best Buy 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.

If a controlled-release feed has not been added already, use a Best Buy controlled-release fertiliser. Read our review to find the best controlled-release fertiliser. 

What makes one compost better than another?

Whether you buy multipurpose or specific-use compost, good structure and aeration are 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.

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.

Does quality vary between bags of the same brand?

You could be forgiven for assuming that one bag of compost would be the same quality as any other bag of the same brand. But this isn't always the case.

Our compost trials have repeatedly found dramatic differences in how well plants grow in composts from different bags of the same brand.

How do growing bags compare to other bags of compost?

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.  

What about reformulated composts?

Composts change for a number of reasons, such as availability of ingredients, cutting costs, improving performance or reducing peat content.

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.

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.