How to reuse compost in your garden: experts reveal their secrets for successfully reusing this nutrient-rich soil amendment

Whether you're trying to reduce your garden waste or repurpose old compost, there are multiple benefits to using old compost from pots.

If you're surrounded by barren plant pots and rather sad-looking compost, you may be thinking it's time for a trip to the garden centre. However, if you want to reduce costs with your gardening this season, you'll be glad to know that your used compost can be just as good as the fresh stuff.

Reusing old potting soil can help you transform your garden on a budget and keep your garden waste to a minimum. You just need to know how to prepare the compost for reuse and how to get the most benefits out of the stuff.

How to reuse compost in your garden

Even when we've done all we can to protect our plants from frost and heavy rain, it's pretty common for them not to make it through the winter. This usually means a few empty pots with old compost and a withered-up plant.

However, before you banish the compost to your garden waste bin, there is a way to revive it so you can use it again. Just because it's been used before doesn't mean it can't still provide your new plants with nutrients; there are just a few things you need to do before using it again.

"To improve the structure of previously used potting soil, you need to make sure it's free of old plant matter, removing old roots and debris by placing the used compost into a wheelbarrow or large tub and breaking up any clumps and removing any plant debris as you work your way through it," explains Lucie Bradley, gardening expert at Easy Garden Irrigation.

"For both previously used potting soil as well as old stored potting soil, you can restore the texture and break up any compaction by adding perlite or vermiculite, using approximately one part perlite to 3 parts potting soil, more if it is very compacted. Ideally, moisten the perlite or vermiculite before mixing it into the compost so that it mixes in evenly and doesn’t draw moisture from the soil," she adds.

If you're looking to add some of the best plants for shade to your garden, then you may want to try improving the texture of your old compost.

"You can improve the texture of the potting soil and make it more moisture retentive by mixing in coco coir or peat moss - again, a 50/50 mix is good to restore aeration and moisture retention. Soak the coco coir or peat moss before mixing it with the potting soil so that it is incorporated effectively," recommends Lucie.

Lucie Bradley

With over 28 years working in the garden industry, Lucie has been fortunate enough to spend every day speaking to both amateur and professional gardeners. Encouraged to garden since she was old enough to walk, she believes that you can never know everything about gardening, as it is constantly evolving.

Can you use the same compost twice?

Reusing things in the garden isn't just a great way to save some money, but it's fantastic for the environment too. In the same way you can reuse household waste in your garden, your compost can be given a second chance, too.

"You can use the same compost twice, but it is likely to be depleted of nutrients and compacted. Due to this, it will need to be revived before use, and it is best to use it for purposes other than planting," explains Richard Barker, horticulture expert at LBS Horticulture.

"However, if the compost previously contained plants that died of a soil-borne disease or if it is very mouldy and slimy, it should not be reused," he adds.

"It is safe to reuse compost, as long as the previous plants within the compost were healthy and free of pests or diseases. You should never reuse compost from plants that were infected with soil-borne diseases," finishes Richard.

Once your compost is properly prepped, you can use it to add some of the best fragrant plants to your garden and give it a spring refresh.

Richard Barker

With 4 years in the industry, Richard is an expert in horticulture and the commercial director at LBS Horticulture. He is keen to share his knowledge with both experienced and beginner gardeners, and prides himself on keeping up to date with the latest horticultural trends.

Garden Designer and Influencer Ish @Gardening.with.ish on TikTok explains, "Can you reuse old compost? Now the quick answer to this is yes, you absolutely can but it takes a few extra steps first."

To demonstrate his method, he shows a terracotta pot filled with dried compost and old stems, which were once blooming sunflowers. He says, "Our old sunflowers in here have had quite a good root base in them so I'm going to show you how to clear up your soil and get it prepared ready for next time."

"To make life easier don't hesitate just take this and put it in a big tub like that first and that will help us see what’s going on in the soil. Now you can see from the bottom of the pot I've added in some gravel and that's okay, that will work as additional drainage, so I'm not too worried about that," advises Ish as he dumps the old soil into the container.

He goes on to explain that even though there can be a lot of root base left over in your old soil, most of it will have been broken down through the winter so it's fine to be left in there. However, you will need to give it a good mix and remove weeds, stems and bigger roots.

"Now that those bits are discarded, I've got some organic material," Ish explains. "But as you can imagine it's still massively lacking in rich nutrition which new plants need so I'm going to just take some freshly rotted compost and add about 25% of this to 75% of the old soil and what that does is replenish some of the nutritional value in that organic matter."

How do you make old soil good again?

You can revive old compost easily with just a few steps, and unlike when your soil type is low quality, it's much easier to bring it back to life.

"Potting soil which has been used to raise plants before will have been depleted of nutrients as the plants have absorbed them," says Lucie.

"So to ensure that the potting soil contains sufficient nutrients to support healthy growth, you can either mix old and new potting soil - so a 50/50 mix would work. Or you could add fertiliser into the old potting soil, using either a low-release fertiliser or a balanced granular feed," she recommends.

You can also follow the previous steps given by Lucie, which help improve the potting soil's structure and texture to give your plants the best chance for growth.

"If you are concerned that the potting soil may contain disease or pests, then you will need to sterilise it, which means heating it to at least 180 degrees Fahrenheit but not higher than 200 degrees, as this can produce toxins in the soil," adds Lucie.

Alternatively, you can use boiling water to sterilise potting soil. Simply cover it with enough water to completely saturate it and leave it covered for 30 minutes in foil.

Can you use compost that is 2 years old?

If you've not decluttered your shed in a while, you might be wondering if there's an expiry date and how long you can really hold onto a bag of compost for.

"Although there is no formal ‘best before date’ with compost, there really should be as it definitely is not at its prime if you don’t use it until it’s over 24 months old. Even if you have kept the potting soil in a sealed bag and stored it somewhere dry, cool and dark, which helps to maintain its quality, after two years, its nutrients will have reduced, its structure will have become denser and more compact," explains Lucie.

She also points out that you might find some white mould inside the bag, which won't be harmful to your plants; it actually just shows the compost is nutrient-dense.

"So, after two years, you shouldn’t just open a bag of potting compost and start using it as it simply won’t be as good for your plants, but you don’t need to throw it away either. You can rejuvenate it, or you can use it in different ways in your garden, such as adding it to your compost heap or using it as top dressing in garden beds or mixing it directly into your garden soil," she continues.

Using a pH soil tester can be a huge help in figuring out what state your compost is in and how it can be improved by adding pH neutralisers.

Gardening can feel a little more challenging when your soil quality is naturally poor; however, several plants are happy to grow in poor soil. As well as improving your soil, it can be a good idea to choose more suitable plants that thrive in the specific conditions your garden has.