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Recycling and reusing old compost

Val Bourne ( 01 June 2015 )

Recycling is the gardener's watchword - even old potting compost. But it's not that straightforward. So follow our guide to successful re-use of old compost.

Gardener potting a plant
Used potting compost should not be used for seed sowing or propagating

Recycling has never been as enthusiastically received, and never more necessary, than now. This applies to garden waste, too. But when it comes to reusing old potting compost, is it a good idea? Well, a guarded yes and no.

Old potting compost cannot be reused for seed sowing or propagating unless it has been effectively sterilised because it might contain the eggs of insects (like vine weevil or flies), or pathogens that might lead to disease.

Related: how to improve your soil.

Sterilising soil

Unfortunately sterilising soil involves high temperatures and it’s a smelly process - rather like fermenting hops. So this is not at all viable for many home gardeners, although there are sterilisers on the market.

Reusing loam-based compost

You can recycle friable loam-based composts by adding them to the ground to improve soil structure, or using them as a moisture-retaining, weed-suppressant mulch.

If you add a fertiliser to the loam-based compost you can also pot up mature plants with it. I have a spent-compost heap close to my own shed and greenhouse that I use to pot up divided perennials.

Related: how to make a compost heap.

Avoid peat-based composts

Gardeners care about the environment and extracting peat is known to be damaging to plant species and habitat. So we should look at other forms of compost in an attempt to find one good enough to replace peat.

The government has set 2020 as the date when all compost sold to gardeners must be peat-free. Peat-based composts are impossible to rehydrate once they dry out. They can form dry balls in garden soil so you need to take care how you use them. They are not as easily recycled as loam-based products which contain sand, silt and clay.

Green waste recycling

A significant change has occurred in recent years in the way local councils deal with green waste. If you use your local council waste station, you’ll be aware that they are composting green material from gardens, sterilising the product and then selling it on, rather than putting it into land fill.

Many councils are selling it back to their residents and others are supplying commercial companies.

So there is no reason why you couldn’t put spent compost straight into a green waste bin – it will still be useful. Contact your local council to see what measures they are taking – and if they’re selling their own bags of compost.

Related: how to help your local area be more environmentally-friendly.


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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.