Whether you're a new gardener using containers or an expert with green fingers. One thing that you may end up with at the end of each gardening year is used or spent compost. You may be wondering what to do with it rather than simply put it in the garden bin. This guide is going to give you 3 ways to recycle old compost reducing your carbon footprint and reusing this precious organic gardening resource.

Compost is the life force of many gardens. Whether you’re buying it in bags from the garden centre (hopefully peat-free) or making your own with composting bins, this black gold is a multi-purpose wonder feed for the garden. However, most gardeners I speak to don’t know what to do with compost once it’s finished feeding your plants or once plants in containers have died back.

There’s a variety of different uses for recycling compost so I thought it was a good time to share my top 3 uses for spent compost!

  1. Mulching your garden borders
  2. Improving lawn seed germination
  3. Speeding up existing compost heaps

What’s the difference between compost and soil?

A number of people confuse compost with garden soil. The two are very different.

Soil is a mix of 5 key ingredients that are naturally occurring. Organic material, water, nutrients, minerals/ rock particles and organisms. Compost on the other hand is a man-made material from organic matter usually found in the garden. Its usually made of a mix of green matter (nitrogen-rich clippings) and brown (carbon-based) material such as twiggy woodier material. It creates a highly nutritious material that breaks down over time. When this breaks down into the soil it becomes humus (not the same as the delicious chickpea-based snack).

Garden Ninja holding out soil
Soil is a mix of 5 naturally occurring ingredients. Stable and able to support plants for their lifetime.

Compost is absorbed by the soil, used to feed plants, retain moisture and act as a temporary growing media. It has a limited shelf life as it degrades and breaks down. So the soil is the stable matter that plants live and establish in, whereas compost is a temporary growing medium that eventually needs replacing or replenishing, unlike soil.

A bucket full of compost in garden ninjas greenhouse
Compost; dark, rich and nutritious! A short lived fuel boost for plants and organisms to feed off.

Why recycle compost?

As conscientious ethical gardeners, we should always be looking to reduce, reuse and recycle wherever possible. There is no point getting closer to nature to then conversely place more of a burden on poor mother nature.

By reducing our demands on the environment we are also helping to protect and nurture our green spaces. It’s also far better to reuse things in the garden than have to pay someone to take them away. It’s win-win!

Compost believe it or not can still have many uses after plants have been grown in it. It still helps improve soil structure, retain moisture and add small amounts of nutrition to the soil in our gardens. So let’s have a look at my top 3 uses for old spent compost.

Garden ninja recycling compost
Removing old spent plants or weeds enables you to loosen old compost so it’s usable again

Should I remove dead or annual plants from old compost?

You’d be surprised how often people ask me whether to take out dead or spent annual plants from compost. The answer is yes. You can prepare your spent composted containers by lifting out the old dead plants and weeds. Shake off as much compost as possible then either compost or dispose of the old plant rootstock cutting it up with secateurs first so it breaks down easily.

Perennial weeds can be hot composted or placed in a bucket for 6 weeks then strained to make weed tea (a liquid feed for the garden).

You can then also use a griddle, riddle or garden sieve to then filter out any bits of old dead root or debris from your spent compost.

Garden Ninja sieving used compost
Sieving old compost removes old roots or bits of debris.

It’s worth noting that if your plants have had known pathogens, diseases or issues during the growing year such as blight you shouldn’t reuse this compost as it can further infect other plants. Use your judgement if you think your compost maybe harbouring nasties. For most gardeners your used compost will be fine as known issues will have been very apparent by looking at the previous plants health.

1. Mulch your garden borders

If you’ve been following my work for some time you’ll know that I love nothing more than to mulch my garden borders. Mulching helps reduce weeds, improve soil structure and can help reduce watering. It’s also a lovely mindful low drama gardening activity.

Used compost is an excellent organic material to help lock in moisture and provide a slow-release feed to flower beds. Even the most tired compost will help improve rich soil texture and help provide a better ‘crumb’ structure to your garden soil.

Mulching a garden with used compost

If you need to any more convincing here’s my garden mulching guide in more step by step detail!

2. Improve lawn seed germination

One of my best secret tips is to use spent compost as a lawn seed hack to help germination. I’ve even trialled this method versus the traditional lawn seeding method where the seed is scattered and then pressed on the soil. However, this leaves lawn seed prey to hungry birds and can mean that the seed never gets the optimal moisture to germinate effectively.

My top tip after reseeding a lawn, whether as a new lawn or lawn repair is to sieve used compost lightly over the seed. Then water well.

What happens is the compost holds onto the moisture far longer than the bare soil will, meaning that seed imbibes water (needed for germination) far faster. I also find that by scattering compost over the lawn seed it is easier to spot the grass seed as it sprouts.

Sieving compost over lawn seed

As the used compost is low in fertility it won’t affect the viability of the seed like a rich compost might. It also can be used as a wonderful lawn top dressing to help improve soil structure and lightly fertilise your lawn.

3. Improve your compost heaps

Whether you already have a compost heap or are about to start a new one, used compost it a great way to give it a boost. The beneficial bacteria already present in used compost can help speed up your home composting methods.

With a new compost bin as your first mix of green (nitrogen-rich) material and brown (carbon-rich material) and then mix in some used compost. This will help create the perfect environment needed for the material to start to break down. As the used compost retains more moisture it also stops your compost bin from drying out which can then slow down the composting process.

Spent compost is a great compost heap booster!

I’ve used old compost to also help improve compacted or smelly compost heaps. Usually, when too much nitrogen-rich matter such as grass clippings have caused the compost pile to stagnate. You don’t need much just enough to help your compost bin along. It can be beneficial to turn it into the existing pile to spread it around rather than just layering it on top.

Composting is a brilliant way to recycle all sorts of garden material from prunings, lawn clippings and growing your own vegetables. This in turn ends up in a cycle of recycling, reusing and so forth. Drastically reducing your garden waste! if you’re thinking of starting a new compost bin, my guide below should help set you up for composting success!

Summary

I’m a great believer that the process of successful gardening involves understanding how everything is connected. Then working with these connections for a more harmonious gardening experience. That even our organic garden waste has a cycle back into the earth which saves on waste to landfill.

By reusing your garden compost in one of these ways you can improve your garden with zero additional spend or unnecessary waste. So what’s not to love?

Do you have additional ways you’ve found to use spent old compost? If so let me know below. Why not share your gardening stories with me on Social media?

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You can TweetFacebook or Instagram me with your composting tips. If you need gardening advice why not check out my Youtube Gardening guides and subscribe if you haven’t already!

Happy Gardening!

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One thought on “Used Compost: 3 ways to recycle it

  1. Joan says:

    I’m reusing the compost I grew tomato plants in for planting a few daffodil and tulip bulbs. No idea if it will work but hey, I’ve done it now….!

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