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What to Do With Your Old or Used Compost

To avoid waste while I grow my own vegetables in containers outside our front door, I devised this great trick for using up old compost.

Ideas for how to use old compost.

Ideas for how to use old compost.

What to Do With Old Compost?

Towards the end of the growing season, you may be faced with the dilemma of what to do with all the old, spent, and used compost from your plant containers and grow-bags, especially if you only have a small patio or garden.

Compost and Potting Soil Left Over in Containers

I grow many of my own vegetables in containers outside our front door and, when the plants have finished their growing season, I am left with the problem of how to dispose of the hundreds of litres of old, used compost I have left over. By the end of the growing season, all the goodness from the compost has been used up by the plants. In fact, depletion of the compost's nutrients happens within six weeks, and this is why you need to feed your plants. Many people would consider the old compost useless and simply dispose of it, but this is not the most environmentally friendly option.

Here's how you can re-use old compost left in containers or bags.

Here's how you can re-use old compost left in containers or bags.

What to Do With Old, Spent Compost

  1. Make new compost. Use it to make new potting soil or compost (directions below).
  2. Use it as mulch. Use it as a mulch on top of your flower or vegetable beds. This will not only improve the soil (especially if you have either a very clay soil or a very sandy soil) but it will automatically mix with your existing soil via worms as they come and go through between the layers.
  3. Use it to level your garden. Use it to help even out a sloping garden or border.
  4. As a bottom layer. Use it to partially fill the bottoms of deep plant pots or containers to reduce the amount of fresh compost you need to it fill up (especially for plants that may not need a particularly deep root run).
  5. As a top layer. Spread it over your lawns and rake it in with a grass rake until it is barely visible. This is good for the lawn and it will be taken down by the worms to improve the soil.
  6. To grow carrots. Use it the following year to grow carrots. As carrots require little nutrients, they will actually produce better roots if the old compost is used. Too many nutrients will result in small carrots with loads of foliage instead of larger carrots with less foliage, and also increases the risk of the roots forking.
  7. As bedding. If you have a place where you can dry the old compost out, you can recycle it as bedding for horses or cows, and then it can be composted with the added manure at a later date.

How to Make Good Compost From Old

The following steps can be taken in your compost bin or simply in a composting pile set to the side of your garden.

1. Layer

The trick to mixing old compost with new is alternating layers of the old and new stuff. That way, the new will rot into the old and add the goodness you want for the following year. If you simply pile all your old compost into the compost bin, all you will have next year is a bin full of useless compost. Make sure you include layers of newspaper, lawn mowings, vegetable peelings, etc.

2. Mix It Up

Alternate the types of materials you use in the layers. For example, you could start with a layer of spent compost, followed by a layer of crumpled newspaper, followed by hedge-clippings, then more old compost, then grass mowings, kitchen waste, spent compost, etc. Try to keep the layers no more than six inches thick each time.

3. Keep It Light

It is particularly important that there is air between the layers, so don’t pack them down too tightly, and try to keep the layers thin, as materials such as grass mowings quickly turn into a nasty layer of slime if not enough air can penetrate the pile.

4. Add Worms

If you can find them, try adding as many worms as possible because they will spread the new material in with the old as they tunnel through the compost and help break it all down by eating and redepositing, as nature intended.

5. Continue Adding Layers

As the materials rot down, the level in your bin will drop and you can add more material to the mix.

6. Turn With a Rake or Fork

If you have a compost heap rather than a bin, then you should regularly “turn” the heap using a fork so that the materials all have access to the warmest part of the heap, which is usually in the center.

7. Cover

You will need to cover the heap with a waterproof sheet such as polythene to prevent it from getting too wet in the rainy seasons. If you don't, your compost will take a lot longer to be ready because heat cannot build up sufficiently.

8. Keep Moist (But Not Wet)

Make sure your heap never dries out, and sprinkle with a hose if necessary.

A list of things to add to old compost so you can reuse it.

A list of things to add to old compost so you can reuse it.

Kitchen scraps layered into old compost.

Kitchen scraps layered into old compost.

Worms help naturally recycle compost.

Worms help naturally recycle compost.

Frequently Asked Questions

What about old compost that has been sitting around in a bag?

Compost can lose its growing power if it sits in a bag for too long (over a year). It loses its nutrients, but it can still be used.

Can you re-use old tomato compost?

Yes, but not for prizewinning tomatoes, since it won't have enough nutrients. Reuse it for various uses around the garden (see list above) but NOT to grow the best tomatoes.

Can you re-use old, used compost to plant new plants?

Yes you can, especially after you amend the old compost by adding things to make it richer. I have provided a list below.

Things to Add to Old Compost

  • hair clippings (human or pet)
  • egg shells
  • vegetable peelings
  • newspaper or paper (but not glossy or colored paper)
  • lawn mowings and hedge-clippings
  • tea bags or coffee grounds
  • annual weeds (not perennials, as they will grow back next year if you put them in your compost bin)
  • rabbit or guinea pig or cavy bedding (if it is straw, hay, or paper and not artificial)
  • any vegetarian pet's waste (not from a meat-eating pet such as a dog or cat)
  • cardboard egg boxes
  • wood shavings
  • old vegetable foliage such as the potato haulms, the remains of bean plants, tomato plants, carrot tops, etc. The roots of beans are especially good as they hold nodules of nitrogen, which will be great for next year's crops.

Things Not to Compost:

  • Cat litter or pet waste.
  • Colored or glossy papers.
  • Diseased leaves (the disease will remain in the compost and may infect next year’s plants, too).

Keep these out of the compost if you don't want to attract pests, flies, or rats:

  • Meat or bones (cooked or raw).
  • Cooked vegetables.
  • Plate scrapings or leftovers.
  • Anything containing mayonnaise or dressing.

How Long Does Compost Take?

Your compost should ready for use within about six months so long as it doesn’t dry out. You can also improve the rate your compost breaks down by adding your own urine to it (yes you did read that correctly). Human urine contains bacteria that help compost to rot successfully, so if you can add a bit of pee to the mix, it will help you to make good quality compost more quickly.

Note: Most compost bins have a door at the bottom, so the oldest compost gets used first. This ensures it has had time to rot down properly.

I grow vegetables in containers outside our front door. When the growing season is done, I have a lot of old compost to deal with.

I grow vegetables in containers outside our front door. When the growing season is done, I have a lot of old compost to deal with.

My Story

In Guernsey in the Channel Islands where I live, the local authorities recently ran a promotion to encourage people to compost their kitchen and garden waste. They provided a large number of compost bins at a greatly subsidised price, so allowing members of the public to only pay £10 per bin instead of over £30 (the normal price). These bins each came with a small container to keep within your house to collect egg shells, carrot tops, vegetable peelings, etc. until you get round to transferring them into your compost bin. They also provided a CD on how to make good compost.

I bought three of these compost bins and, using the knowledge I already had of making compost from house and garden waste, I realised I could combine this waste with my spent compost and in effect re-introduce goodness to it so I could use it again next year.


Cindy Lawson (author) from Guernsey (Channel Islands) on November 22, 2017:

Don’t know what you are apologising for diogenes, nothing in your comment offended me.

diogenes from UK and Mexico on November 22, 2017:

Sorry again! I need to get over myself! Bob x

Cindy Lawson (author) from Guernsey (Channel Islands) on November 22, 2017:

Hi diogenes, great to catch up with you after so long. Yes, I am still growing my vegetables every year and gradually taking over the lawn with dwarf fruit trees too :)

Cindy Lawson (author) from Guernsey (Channel Islands) on November 22, 2017:

Thank you RTalloni, I always manage to use mine up without any wastage.

RTalloni on November 22, 2017:

Using spent compost is an important part of gardening. Glad to see the topic well covered in this post.

diogenes from UK and Mexico on November 22, 2017:

Wha...? "I have to pull out my carrot and have a pee in the petunias....? haha

Wonderful article as usual, Misty- long time no see?? I have wondered in the past whether the old compost was any good and what to do with it.

Still growin' those 'marties, eh??

Bob x