Bagged Compost Isn’t Cheap So Reusing It Makes Sense. Here Is How I Reuse Old Compost From Pots, Containers and Potato Bags. 

The Internet is full of compost questions. Check Google and all of the ones you see in this page’s content box are common Google searches. Let’s Reuse Compost and garden more sustainably.

Let’s look at these questions one by one. But let me start by saying “old” compost is like gold dust. It has value and should never be thrown away. And in the next few paragraphs I’ll explain what you can do instead.

Can I take old compost to the tip?

Yes, you can but its like throwing money away and is unsustainable as well.  It’s far better to reuse the compact wherever you can. I can think of a few cases for throwing it away but have never thrown any away myself. And in 99% of situations there’s no reason for any one to do so. 

What do you do with old compost from pots?

Use it again. In this article I’Il explain how to do that. 

Can you reuse the same compost?

Yes, it can be reused many many times. I’ve never thrown any away in my whole gardening life. 

Can you revive old compost?

Yes, it can be used in many different ways. 

What can you do with last year’s compost?

When rejuvenated it cab be used to grow anything that you’d use new compost for. Though, with some high yielding crops such as tomatoes I’d mix it with new compost before planting the tomatoes. And I’ll explain later how I’d mix if together .. or not .. before replanting. 

Can I use old compost for bulbs?

Yes. I’d tend to mix it with some new compost though, as once bulbs have flowered they need nutrients to build up next year’s flowers in the new bulb that is being formed. And there are a few other things I’d do to ensure success. More on that in a moment. 

Can you reuse grow bag compost?

Yes. But remember grow bag compost is usually the poor grade compost that wasn’t good enough grade to match seed compost standards. So you need to take that into account. Plus, if it has been used to grow a hight yielding crops it’ll need a nutrient boost. 

Does old compost lose its nutrients?

Yes and No.

If we are talking about compost made from organic materials, either home made or bought in a sack from a retailer, it should be pure organic matter. So over time it will slowly break down and release more nutrients. But the key word here is “slowly”. And if you want to grow a fast growing crop it’s best to be sure there are enough nutrients. So I’d add some organic fertiliser. Personally I favour a handful of Vitax Q4 per large container, mixed well into the compost. But any good quality organic fertiliser will also work. But having said that don’t go for those that are high nitrogen at the expense of potash unless you know what you are doing. Especially if trying to grow fruit or flowers. 

Those composts that have additional ingredients, such as soil, are likely to be more nutrient deficient after growing a hight yielding crop. This is because soil cannot decompose and provide more nutrients. 

But the above will of course depend on how high yielding the crop was, how much feed was added and several other factors, so it can only be a generalisation. 

How to regenerate compost

How do you revive old compost?

How do you rejuvenate old compost?

Can I reuse compost?

Four questions and one answer.

This is how I regenerate or rejuvenate compost.

At the end of a growing season the compost may well be a bit dry. If it is I firstly water it to get it back into a decent state. If it is really dry I do this over several waterings, often over several days. Many composts have a wetting agent added when processed.. This ensured they didn’t easily dry out. But the effect decreases over time.

Once compost gets dry it can be hard to rewet. So what is a wetting agent.  Basically it is a product that reduces surface tension in the water which means that it can flow into the spaces within the compost or soil. It’s a bit like the dish washing products we use in kitchens or like baby shampoo. In fact, on an amateur basis I have used both of these products. But they should be used sparingly. A few drops in a gallon (5 litres) of water is enough. In fact, too much dish washing liquid could prove toxic to some plants because they use salt to thicken the soap product. And luxury products, being thicker, just contain more salt!

Once the original compost is moist I then tend to boost the nutrient levels with some organic fertiliser. 

Next I add more compost to dilute the old compost. It’s not that anything is wrong with the old but I prefer to back both horses in the compost stakes. 

What About Weeds?

And there’s another reason. Old compost may contain a few weed seeds. Either from a stray weed that has grown in the compost, OR one that has blown in on the wind. And here’s the real secret. I don’t mix the old and new together. If I did I’d be giving the weed seeds chance to grow.

What I do is to put the new compost on top of the old. So we have a layer of old in the bottom on my container or pot and new on top. The new suppresses lots of weeds .. should they exist. 

Now I’m ready for planting and I treat this mix just as I would a brand new one. 

Beware Pest and Diseases

I said I’ve never thrown away old compost. And I haven’t. 

Robin on a branch
Robins remind me of spring as they sing in the January Garden. This one 

But if I had diseases such as onion white rot, or sclerotinia of any sort, I’d not want to reuse the compost for vulnerable crops. I’d reuse it in a situation where the disease didn’t matter. Perhaps to lighten the soil if I were planting a tree for example. I’d want that compost used with where it it’ll do no harm. 
The only exception would be if the compost were infected with sclerotinia. That I might destroy rather than spread the sclerots.

Before I use my compost and recycle it I like to check for grubs of any insect that eats roots and slugs. I pick through the compost and if I find any I use nature’s helpers, eg Robins, to clear them up.

Take the compost and spread it thinly on a large sheet of plastic. I find my robins will pick through and eat anything they can find. After a while I tend to move the compost around a bit to ensure the robins can get at any larvae, grub, slug, or slug egg hidden by the compost. I repeat a few times until the robins give up. If they are satisfied, so am I.

What Will Grow in Reclaimed Compost?

I see some gardeners advising against some crops. But I tend to grow anything and everything in rejuvenated compost. Provided of course that the plants would grow in fresh compost. 

Why Use Organic Fertiliser in Compost?

I use organic fertiliser for one simple reason. It is slow release. 

How Many times Can Compost Be Recycled? 

I don’t think there’s a limit. It can go on forever unless diseased. 

Other Compost Recycling Tips & Uses

Old compost can also be used for mulching. Just spread it in the garden where it’ll do most use. 

Alternatively, add it to your compost heap. Then it can be recycled as part of your next batch of finished compost. 

Will You Now Reuse Compost?

There’s More On Compost Via This Link.

2 thoughts on “How To Reuse Compost In the Garden

  1. Joan Williams says:

    Good tips Stefan. I keep last years compost in plastic sacks which keeps it moist, before adding fresh compost and blood, fish and bone. This is used for the flower trough’s and hanging baskets, always fine. My homemade compost is mainly used for the vegetable garden along with seaweed and horse manure.

    1. Stefan Drew says:

      Sacks area good idea.

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