Does Old Compost Lose Its Nutrients?


Compost is essential for gardening and hastens plant growth while improving health. However, like many other organic substances, compost decomposes with time. This breakdown process typically leaves many gardeners worried about its efficiency and continued contribution to their plant’s health.

Old compost loses its nutrients as time passes due to several factors, including the natural decomposition process and how it’s stored. As a result, aged compost, whether used or unused, offers fewer nutrients than its fresher counterparts.

The rest of this article will discuss why and how this happens in more detail and explain other crucial points about using compost, including how to tell if it’s gone bad. I’ll also elaborate on the potential reuse of compost and how best to do it.

How Long Do Nutrients Last in Compost?

Compost faces one major problem—decomposition. As it decomposes, compost will lose more and more of its nutrients to the soil. These essential nutrients will continue to leach into the ground until the compost loses all its beneficial nutrients.

Thankfully, this takes some time, so nutrients in compost can typically last for a year or two. That said, some other factors could affect the rate of nutrient loss.

For example, leaving compost in a pile could lead to higher value loss. This loss is because the compost becomes much more compact due to faster decomposition. Bagged compost often suffers a similar fate for the same reason.

The microbes that feed on waste are often the culprit in piled and bagged compost’s increasingly compact structure. And if you store compost, you’ll notice that the contents of its bag will drastically reduce as time passes.

In addition to nutrient loss and higher density, the compost may even start to rot if fungus comes into contact with it.

You can prevent this problem by controlling your compost pile’s moisture levels and storing it appropriately. And if you want to keep your compost for a long time, it’s best to do so in a cool, dry place.

Covering the pile will also help conserve its nutrients for a slightly extended period.

Sometimes, after the bagged compost has lost a lot of nutrients, the material might form a concentrated, viscous liquid. This liquid, called leachate, contains a high level of much-needed nutrients like nitrogen and phosphorus, and it’s best not to throw it away.

Instead of wasting it, I recommend you use it as fertilizer for your garden soil.

There are dozens of commercial compost on the market, and Charlie’s Compost (available on Amazon.com) is one of the best I’ve come across since I started gardening. This compost has organic materials made from natural, non-toxic matter. It also provides a long-term nutrient supply for your garden, regardless of what you’re growing.

When Does Compost Go Bad?

Technically, compost never goes bad, despite all its organic components. However, it will continue to decompose and lose structure and nutrients over time. And while this process is standard for all compost types, it might be bad news for your garden.

Of course, for your plants to survive, you’ll need to provide them with a constant supply of nutrients, which is where compost comes in. Compost is an organic substance that often contains animal manure, plant foliage, and materials like straw and sawdust. It doesn’t have dangerous pathogens and is not harmful to any garden life.

Undoubtedly, compost is precious to many gardeners. Unfortunately, this organic substance’s nutrients and other helpful compounds don’t last forever, even though it contains many much-needed nutrients like nitrogen, phosphorus, and potassium.

And although compost doesn’t expire, it can fail to provide your plants with what they need to thrive.

Here are some telltale signs that will let you know if your compost has become less beneficial to your plant:

  • The compost smells terrible.
  • Absence of worms and bugs.
  • The compost doesn’t get heated.

Let’s explore these signs in more detail.

The Compost Smells Terrible

Terrible-smelling compost is often a sign that the material is going through anaerobic decomposition. Unlike aerobic decomposition, this type of decomposition occurs without air.

Most compost naturally has pleasant, earthy smells. However, compost will quickly become stale and foul without air in its decomposition process. This process typically leads to unbearable smells.

Absence of Worms and Bugs

Compost should naturally have a healthy amount of bugs and worms crawling through it. It might take some time for you to notice these worms and bugs in newly-applied compost, but with time, they will eventually become a lot more commonplace. 

If you fail to see these worms in older compost, it might be a sign that the compost has lost a lot of vital materials and nutrients.

The Compost Doesn’t Heat Up

Heat production from compost largely depends on the pile size, the amount of moisture present, and its carbon-to-nitrogen ratio. The heat has to be present for decomposition to occur. It’s also necessary when trying to make homemade compost.

When heat is absent, it’s usually because the pile may be too wet, dry, or contains an inadequate amount of nitrogen and decomposable materials.

Ultimately, leaving this compost on your garden bed can harm your plant’s health. It will quickly undergo anaerobic decomposition (instead of aerobic), which leaves behind a rancid smell and releases toxic chemicals into the soil.

Can You Reuse Compost?

You can recycle old or aged compost as many times as you like. You can also “revive” your compost for use in your garden. These terms may sound similar – “revive” and “recycle” – but they are slightly different. 

When “recycling” compost, we mean using it for other means like mulching, potting mixes, and tilling into the soil.

However, “reviving” compost means adding several organic materials to replace all the lost nutrients and regain some structure for continued use.

How To Revive Old Compost

If your vegetable or plant garden has experienced diseases like Onion White Rot, it’s not a good idea to reuse the compost since doing so will increase the chance of a recurrence. In this case, it’s best to dispose of this compost.

That said, most compost is usually safe to revive as long as there’s no chance of infection. 

It is easy to revive and repurpose compost—let’s dive into these steps in greater detail.

1. Inspect Your Old Compost

Before doing anything else, you must examine your current compost and ask essential questions. How long has it stayed in the bag, pile, or on your soil? Is there insect activity? Does it heat up towards the center?

Also, try and monitor the nutrient level in your soil, and check for any other foreign substances and chemicals. By monitoring this, you will be able to watch how far along the decomposition process is and know when it’s due for a revival.

You will need a soil test kit to do this, and an excellent one for you to consider is the Rapitest Luster Leaf Digital Soil Test Kit (from Amazon.com). It tests for the amount of Nitrogen, Potassium, and Phosphorus in the soil. You can also use it to test pH, which may alter by the process of anaerobic decomposition.

2. Mix Your Compost

Mixing old compost with a fresh batch is always a good idea. For the best results, combine these aged and fresh compost in layers. If you use this method, it’s much easier for old compost to mix with the new and become a rich source of nutrients for your plants.

However, keep the layers light because it needs air to activate aerobic decomposition. Each layer should be no thicker than six inches. 

3. Add Some Organic Matter

One of the quickest ways to revive your compost is using organic materials like wood scraps and leaves. Adding these will help reactivate the decomposition process and, once again, allow you to reuse aged compost rather than throw it out.

Organic substances like worms, newspapers, sawdust, and even waste from the kitchen will do the trick. In addition to dead worms providing nutrients, the living ones will help to spread the old compost with the new as it moves around, trying to eat all the organic materials they can. These creatures will also redeposit waste that contains lots of nutrients for your plants.

4. Ensure Your Compost Remains Moist

When your compost is not moist enough, it will significantly slow the decomposition process. The microbes, majorly bacteria and fungi, won’t be able to function as efficiently. Luckily, you can quickly rectify this issue.

To solve this, add some water using a watering can. Although rainwater is best for this, ordinary water will do. Remember to apply evenly to avoid your compost getting too wet.

If possible, try to mix your compost as you water. Mixing will ensure water gets to every part of your compost mix.

5. Use the Compost As Mulch if It’s Too Spent

Although compost can last for years, there will come a time when it’s too spent. When it gets to this stage, it’s better to use it as mulch rather than dispose of it. You can use this old compost as a top layer for your garden or as a garden leveler.

Not only will this prevent wastage, but it will also prevent the growth of pesky weeds.

Conclusion

Old compost does lose its nutrients over time due to the natural process of decomposition and leaching. However, you can quickly revive it to prevent wastage.

You can repurpose your aged compost can as a mulch for your plants. If your compost doesn’t smell bad, heats up when decomposing, and contains a healthy amount of worms, you’re fine. Otherwise, you must revive your compost if you want it to be beneficial to your garden or potted plants. 

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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