Where Can I Dispose of Old Compost?

Emma Loker Headshot - DIY Garden
Written by: - Gardening Expert

You’ve got innovative ideas for your garden. Out with the old, in with the new. But what about all that old compost?

In this article, we uncover the ins and outs of old compost. Find out what it is and the benefits of reusing it (there are lots!). By the end of it, you’ll know what to do with old compost and how to keep your compost heap healthy. You’ll be a compost expert!

What’s Compost?

Most people get garden soil and compost mixed up. Soil is made up of organic matter, organisms, minerals, water, and nutrients. Compost, on the other hand, is made of green matter, like leaves, and brown material, such as twigs. 

The critical difference between the two is that compost is manmade. It’s also nutrient-rich because it retains the nutrients from broken-down waste. Soil absorbs compost and uses it to feed plants and keep the ground moist.

Soil also lasts forever, whereas compost’s days are numbered. How long does compost last, you ask? Compost loses the majority of its nutrients within 6 weeks.


Why Reuse Compost?

Your containers, beds, and borders look great when the plants are thriving. But when it’s time to replace them, you’re left with a load of old compost lacking nutrients.

It’s a general consensus that once the compost is old, it’s spent, useless. That’s far from the case. Much of gardening is about reducing waste. We attempt to give something back to the earth because we humans take so much! But throwing away old compost is increasing your carbon footprint. 

Even old compost can invigorate soil, giving it structure, moisture, and nutrients. Additionally, it’s too costly to keep buying it new for those of us not made of money.

Asking yourself what to do with spent compost? Here are 4 solutions:

  1. Make mulch
  2. Boost your lawn
  3. Grow root veggies
  4. Revitalise your compost heap

Let’s take a look at how to make the most of old compost using these methods. 

Making the Most of Old Compost 


1. Make Mulch

Mulch is a garden saviour as it minimises weed growth, improves the ground’s moisture content, and enhances soil structure.

You can use old compost as mulch on your flower and vegetable beds. Using old compost ensures your plants are getting a consistent, slow-release feed, which means less money spent on fertiliser! It’s also water-retentive, so it packs the soil full of moisture. 

Put a thin layer (around ½ an inch) of your old compost on the soil surface around your plants. Cover up any spaces between your plants because this is where weeds love to spring up and annoy us! Then, leave the worms to do the rest. They’ll mix your compost with the existing soil. There’s no need to mix it yourself!

Just remember, weed first, then mulch! That way, all the nutrients and moisture go to your revered plants, not the pesky weeds.

2. Boost Your Lawn

Every now and then, the grass can look a bit dilapidated. Use old compost to boost seed germination. Sow your grass seeds according to the packet instructions. Then, sieve a light layer of old compost over the top. Once you’re done, give it a thorough watering.

Garden soil struggles to keep hold of moisture. Compost, on the other hand, soaks up the stuff. Adding compost after spreading grass seeds packs in the moisture, allowing the seeds to germinate at a much quicker rate. It’s also easier to spot the grass seeds sprout against the compost’s dark, rich colour. 

Make sure you’re only using your old compost for this. Anything that’s too nutrient-dense will lessen the fertility of the seeds.

3. Grow Root Veggies

On the whole, old compost shouldn’t be used when attempting to grow vegetables. Old compost is seriously lacking in nutrients. Vegetables typically need nutrient-rich soil to thrive, so old compost is no good.

Although it doesn’t contain much in the way of nutrients, old compost still accommodates perlite and humus. Root vegetables love these!

Carrots don’t need much in the way of nutrition, and they actually grow better without it. Sowing carrot seeds in nutrient-rich soil just creates bushy carrot tops and little carrots! For sumptuous, sizeable carrots, use old compost. 

Another root vegetable that benefits from old compost is beetroot. In fact, any slow-sprouting seeds love the stuff!

4. Revitalise Your Compost Heap

Wondering how to regenerate spent compost? Just add it to your compost heap!

Old compost is excellent for stinky compost heaps, nutrient-lacking compost heaps, and compost heaps you haven’t even started yet! 

If you’re starting a compost heap from scratch, mix brown, carbon-rich materials with green, nitrogen-rich matter. Then add in your old compost! 

Used compost contains bacteria which helps to speed up the breakdown of your green and brown organic materials. Because it retains a tonne of moisture, it keeps your compost heap nourished and prevents dryness. 

Have you got a pungent compost heap? This happens when green matter dominates your pile. Adding old compost can help to stabilise your heap and stop it from smelling so awful!

There are some other secrets to making top-quality compost. Let’s go through them, one by one.


Alternate Your Layers

The first secret is layering, my friend! Don’t just chuck everything on without a second thought. A genuinely effective compost heap will have alternating old and new material layers. Layers should be less than 6 inches in thickness. 

Try a layer of spent compost, then a layer of newspaper, then maybe a layer of food waste? You can layer however you like. You can chuck in tea bags, veg peelings and roots, eggshells, plant clippings, hair clippings, straw, hay, paper, and cardboard egg boxes. 

The options are endless, really! Just remember to layer it.

Let it Breathe!

More sunlight = better compost. Thinner layers will allow more light to penetrate the compost. Don’t pack your layers down too much, or your compost heap won’t be able to breathe, and this will hinder the breaking down process.

It can also cause stinky gunk to develop, which you do not want!

Turn it!

Use a rake or fork to turn your compost heap. If you have a compost bin, ignore this step – this doesn’t apply to you!

You want every layer of compost to have a chance of getting warm because warmth allows the bacteria to do its work. Otherwise, you’ll have some bits that are broken down and other parts still intact.

Add Worms

Worms are a gardener’s friend. They’re especially helpful with compost heaps! They work through the layers, mixing it all up and helping to break the matter down. 

You can rest easy knowing worms are doing your work for you!


READ NEXT: What Can You Compost?

When Not To Reuse Old Compost

One risk of old compost is that it might be housing insect eggs or pathogens likely to riddle your plants with diseases. 

Don’t reuse the compost of plants that have suffered from diseases. Using this again will just spread these to more of your adored plants.

Additionally, don’t use old compost that still contains weeds. Be sure to weed the compost before use. Otherwise, you’ll be aiding the spread of unwanted plants in your garden! 

If you’re growing tomatoes, it’s wise to do out with the old and in with the new. Tomatoes need nutrient-rich compost and they’re mightily susceptible to pests. There’s no point risking exposing them to potential pathogens with old compost.

Get Reusing!

Now you’re an old compost expert, you know what you have to do. Use your old compost as mulch to encourage grass seed germination, grow root veggies, or make a killer compost heap. Just don’t throw it away unless it’s harbouring pests! And remember, keep it away from your tomatoes.

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