Can I Re-Use Potting Compost?

Can I Re-Use Potting Compost?

hands holding compost

It is conventional wisdom that you should discard used potting compost but, given that we are all trying to be more  sustainable, I think we should review this advice. 

Unless your potted plant died from a soil borne pest or disease (e.g. vine weevil or verticillium wilt), I see no reason why old compost can't be reinvigorated and used again. 

 

Old compost that looks tired, dry and full of roots is probably best broken up and used as a protective mulch in other pots or elsewhere in the garden. 

Tired compost will be low in nutrients, but it will help retain moisture, suppress weeds and add some organic matter to your garden soil. Alternatively you can add it to your compost heap, where it can recycled along with the rest of your garden waste. 

Mixing old compost

Compost that looks fresher - maybe 3 years old or less - can be re-used if more nutrients are added. If it is very compacted, you can 'open it up' by using sand, perlite or horticultural grit. 

I would take all the compost out of pots, especially large ones; as constantly amending the upper layers will lead to a compacted lump at the bottom that roots will struggle to penetrate. 

Start by breaking up the compost with your hands. Then mix in your chosen drainage material at a ratio of about 4: old compost to 1: sand, grit or perlite. 

You can use this mix to partially fill larger pots because, as you know, feeding roots tend to stay closer to the surface while moisture-seeking roots will grow further down the container. It is therefore fine to use your recycled mix in the base of a pot, and top up the upper layers with a new (and therefore higher nutrient) compost. 

a scoop of healthy compost

If you want to make a higher nutrient compost for general potting, I would mix the recycled blend with new, fresh compost at a 50/50 ratio, and add a slow release fertiliser. 

I prefer a natural fertiliser like our 'Seafeed' seaweed and poultry manure pellets, added at around a 20:1 compost to manure ratio. Throw the new mix into a pot, and away you go again!

Seafeed slow release pellets

4kg Seafeed Natural Seaweed Extract & Poultry Manure Fertilizer

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