Coriander seedlings growing in fine compost.

How to Use Compost For Maximum Benefit

After months or even years, your home made compost is ready. It’s matured, darkened and gained a fresh earthy smell. 

Now it’s time to use it – and what a lot of uses there are for it! 

In fact, the many uses of compost all around the garden mean that even the keenest of gardeners usually have to buy some compost in. 

Let’s take a look at some of the ways you can use compost to grow more and grow better. 

Contents

Before you apply

Screening compost before use.
Screening can help you get finer compost.

Before you apply your compost, you need to be sure your compost is ready. It should have cooled down, and ideally been left to mature for some time for the worms to work their magic. The colour will have deepened, and it will have a fresh, earthy smell. 

It’s also worth checking to see how much woody elements there are in the compost.  If there’s a little bit of wood/twigs/bark in the compost, it won’t hurt. In fact, it may prove beneficial for the fungi in your soil. 

If it’s very woody, it’s worth sifting the compost before applying it to the garden, as decomposing wood can steal nitrogen from the soil. 

If you’re not sure if the compost is ready, it’s worth testing the compost before planting in it. 

There are many ways to test compost, but the easiest is simply to plant some seeds in it. If strong, healthy seeds come up, your compost is probably ready. Testing is particularly important if using manure compost, as it can contain herbicides

Learn more: When is compost ready

When to apply compost

There’s no hard and fast rule to when you have to apply compost – and some disagreement over the best time to apply it. 

Traditionally, compost is often applied in the spring – which may be due as much to rising enthusiasm as the spring sun finally breaks through the long winter months as much as to science. 

However, there are advantages to applying compost in late autumn (or fall, if you are in the US) or early winter. 

  1. Many of the benefits of compost comes not just (directly) from the nutrients but by improving the structure of the soil. By applying compost months before the key planting time, we allow the compost time to benefit the soil.
  2. As temperature begins to rise in early spring, and soil bacteria become more active, that bacteria can start to take advantage of the nutrients from the compost.  
  3. If you dig your soil, it gives your soil time to recover before you plant it. 
  4. Spring to mid-autumn is a busy time in the garden. By late autumn weeds have slowed down, and many harvests have been gathered, leaving more time for working on the soil.
  5. In contrast to store bought fertilisers, the nutrients in compost are insoluble, so you don’t have to worry so much about them being washed out by the rain.
  6. The most growth takes place in the summer, of course, and that’s when plants will be hungriest. But it’s also when the soil bacteria is at its most active, which means more nutrients are available to the plants anyway – especially if the bacteria that makes those nutrients available have had time to benefit from the compost. 

If you think about it, by applying compost in autumn you are also mimicking nature to an extent. 

In nature, leaves fall and plants die in the autumn. They then deteriorate through winter and early spring, providing the soil with decomposed organic material just as new plants start to get going. As plants have evolved to fit this cycle over millions of years, it makes sense to copy it in our garden. 

The quality of your compost also affects when you should apply it. If there is still plenty of fibre in your compost, there’s an extra reason to add it in the autumn when it will continue to break down in the winter, albeit at a slower rate because of the reduced temperature. 

A slight caveat here! Unfinished compost can slow down the growth of plants. However, some heavy feeders such as sweet corn and squash will more happily tolerate – or even benefit from –  young compost. 

Using Compost in No Dig Gardening

Using compost to extend a no-dig bed.
Extending the veg patch.

While traditionally compost has been dug into the soil, no-dig gardening has been gaining ground in recent years. The method was popularised by Charles Dowding, who has for years run a dig v. no dig test, consistently getting better results from the No-Dig bed. 

In No-Dig gardening, you simply apply 1-2 inches of compost to the top of the soil. You can do the same for a new bed, applying cardboard to kill the weeds, and then covering the cardboard with compost, although you may need more compost depending on the soil you are covering.

This is my preferred method of applying compost. Instead of fighting the soil, and damaging the very bacteria and fungi that provides the nutrients your plants need, you are mimicking nature and working with the soil. And again, you are mimicking the very process that takes place in nature. 

There’s another advantage. When you dig your soil, you are bringing up all the weed seeds to the surface and encouraging them to germinate. When you cover with compost, you are burying those weeds seeds deeper, and fewer will germinate. 

It’s also easy. I had an overgrown flower bed this year (they always get less attention than my veg beds!) Instead of spending energy weeding it, I just covered the weeds with cardboard and the cardboard with compost. 

Traditional way to use compost for vegetable gardening

Of course, more traditional gardeners prefer to dig or rotavate their soil (and still get fantastic results). The quantities used are much the same – apply 1-2 inches to the soil and then dig it over. You can also dig trenches and fill in with compost. 

You can also use compost to top dress vegetable plants. Some plants benefit from this more than others.

Raised Beds

It can take a huge amount of compost to fill a decent sized raised bed! My favourite method is to start by adding cardboard over the base, to save digging and kill off weeds. I then get a large trailer load of well-rotted manure in the autumn. I pile the manure up and leave it to further decompose over the winter, and spread a layer of compost over the top. 

Here’s what it looked like the next summer:

Raised bed the year after construction.

Do note that this creates a very rich soil – too rich for some plants. Turnips and radishes, for example, go all leafy and never seem to develop any bulbs. Beans and pumpkins, on the other hand, love it.

An alternative would be to put a layer of topsoil down, and then cover that with a couple of inches of compost.

Once you have established your raised bed, you can maintain it using one of the methods above. 

I no longer construct raised beds in the garden, as slugs do seem to enjoy hiding under the wood. 

Compost socks

Compost socks are commonly used with strawberries. They consist of a mesh tube filled with compost. Research highlighted on the USDA website has shown that compost socks can: 

  • Reduce the chance of black root rot. 
  • Increase the yield between 16 and 32 times when compared to more conventional growing systems!

Compost socks can be purchased. Alternatively, you can make your own. 

  1. Fill an eight inch diameter tube with compost. You can use whatever length is suitable for your garden. 
  2. Lay it on top of the soil where you are going to grow the strawberries. 
  3. Slit the tube every eight inches. 
  4. Plant a strawberry plant in each slot.

Compost Tea

You can also create a compost tea, which is a feed for your plants which is full of soluble nitrogen. Some research also suggests that compost tea may help suppress some plant diseases. It’s important to use only high quality, mature compost. The compost process removes pathogens, but this process does not continue in the cold brewing process you get in compost tea. 

You’ll find many recipes for compost tea. The traditional method to create a leacheate tea is just to place a generous amount of compost in a porous sack. Place the sack in a large container of water.  When you have soaked the compost for a few days, you can fill your watering can with the water. You can refill the container several times before the nutrients are used up. 

Do note that that this tea, because of its soluble nitrogen, is best used as a pick-me-up for hungry plants. The best option for improving the soil long term, and ensuring that nutrients are available for the plants, is still applying compost to the soil. 

Compost tea can also be brewed. This is a more complex process, and there is a lot of disagreement over its effectiveness. See our full guide to compost tea if you want to learn more!

Can’t be bothered to make your own? Compost tea can also be purchased online here or via the link below. 

Replenishing pots

Tulips in pots.

Potted plants live a strange life, constantly drawing fertility from a small area of soil, aided only by the application of soluble fertilisers from a bottle. So replenishing their soil makes a lot of sense. 

A simple topping up of compost once a year can do wonders for your plants. I also like to take my overwintered chilli plants and shake out their roots, then apply a layer of compost at the bottom of the pot.  

You can also use compost to rejuvenate herb pot plants bought from the store.

Should you pasteurise compost before use in pots?

Some sources advise pasteurising your compost before using in pots to kill pathogens. For example, Composting for a New Generation advises heating compost at 200 Fahrenheit (93 Celsius) for two hours before using. I’m not so sure.

We know two things about composting: 

  1. The composting process already kills pathogens. Much is made of the potential for hot compost to kill pathogens, but the maturing process also kills them. 
  2. Much of the benefit of compost comes from the microorganisms that live in compost. What are the effects of applying temperatures which are hotter than those generated at the peak of the composting process? I worry that many of those beneficial organisms could be killed, making them effectively sterile. 

Unfortunately, I haven’t seen much research either way. Until I do, though, I’m going to avoid cooking my compost! 

(Do note that pasteurising compost may, however, be required for certain types of growing, such as with mushrooms.)

Replenishing grow bags

This is all based on my own experimentation, as I’ve never heard of anyone else doing this before. In fact it all started early in the Covid crisis. 

I’d been using my neighbours greenhouse to grow veg for the both of us. As it had a concrete floor I was using grow bags.

Unfortunately, as everyone went crazy for gardening in lockdown it became impossible to get hold of grow bags. As no-dig gardening had worked well for me in the veg garden, I wondered if it would work with grow bags too. 

So I scraped the top couple of inches or so of compost out of the grow bag and replaced it with fresh compost. I also use bottomless pots for my tomato plants, so I filled these with well rotted manure and compost. 

There’s always many factors in gardening, and it’s impossible to tell anything from one season’s results. But the results were far better than the year before. 

Compost for Seedlings

Seedlings in John Innes compost.

Seeds have lower nitrogen requirements than regular plants and require better drainage. What’s more, if the nutrients in compost are too high, seedlings can grow too fast, leading to leggy plants. 

It’s even more important to ensure that the compost is fully matured (you may want to leave compost for longer when making it for seedlings). Compost should be very fine, and it’s a good idea to carefully sift home made compost before using it with seedlings. You can get away with a little bit of wood with compost in the veg garden, but seedlings do much better in compost without wood.  

Ideally, you will mix compost for seedlings with another substance. You can mix one part compost with one part sand. Alternatively, you can mix two parts of compost with one part coir or leaf mould, and add a little perlite. 

The above steps will help maximise the success of your seed germination. That said, some seeds will usually grow well in compost that hasn’t been mixed with sand. Indeed, I find seeds like broad beans and runner beans will do well with even very rough compost. 

I usually, however, cheat and buy compost for seedlings. After all, there’s plenty of use for the compost I make on the veg patch.

Topping up leggy seedlings

If you have seedlings that have developed long, spindly stems, you can add compost around them to help support the stems. 

Flowers

A swing in a flower garden.

Compost works well as a mulch around growing flowers, where it helps suppress weeds and conserve warmth and moisture.

The mix can also deter ants, which dislike the higher moisture levels.

To use, simply apply as a mulch around 1 inch thick around the base of the plant, leaving space between the compost and plants with woody stems.

On the lawn

If you have bare patches on your lawn, you can remove the old turf, replace it with compost and sprinkle grass seeds on the top. 

Your lawn will also benefit from a light sprinkling of compost raked over the top. Don’t spread too thick a layer, as it can smother the grass. When you have finished, the lawn should still look green rather than brown. 

It’s a good idea to water the lawn after you have finished spreading the compost, as this will help the compost to start working its way into the grass. Avoid moving the lawn for the week after spreading the compost to avoid collecting back some of the compost you are trying to get into the ground!

Grasscycling

There’s a lazy alternative to treating your lawn with compost, and that’s grasscycling. All you need to do is forego collecting grass after you have mown the lawn. This is best done when the grass is not too long (the ideal height can vary from area to area), as too thick a layer will smother the lawn. 

I have to admit I do collect the grass, and that’s because, when mixed with other materials, it’s a fantastic compost accelerator.

I am also happy to leave my lawn under fertilised. I enjoy the wild flowers that seed themselves in my lawn, and these plants enjoy lower nitrogen soil. 

Perennial Vegetables

I grow a number of perennial vegetables, including Taunton Dean kale, Good King Henry and Scorzonera (for the leaves, not the roots). I rarely add compost, or indeed fertilise them, and it seems to do them no harm. In fact, they frequently perform better than my annual vegetables.

In contrast to the annual vegetables we usually grow in our garden, these varieties have not been bred over centuries to respond to high nitrogen levels, and they have established roots which allow them to access nutrients more often. I do, however, add compost or manure to heavy feeders like rhubarb, asparagus and Jerusalem Artichokes.  

Trees and shrubs

Unfortunately, there is plenty of controversy over whether to use compost with trees. 

The Rodale Book of Compost advises against putting compost in holes when planting, advising that this can prevent the roots from spreading. This can lead to waterlogging, windthrow, disease and insect problems. 

They instead advise top dressing the soil with compost and watering it in. 

Martin Crawford, in his superb book Creating a Forest Garden, is sceptical over whether compost is needed at all. Instead he suggests a system where nitrogen hungry trees, shrubs and plants are grown along with nitrogen fixers. The nitrogen fixers put nitrogen into the soil, and Mycorrizhal fungi carries nitrogen from plants that don’t need it to plants that do need it. 

Forestry England plant a LOT of trees, so I contacted them for advice. Here’s what Shain Hingston, an operations manager at Forestry England, had to say:

Mixing compost with the soil used to backfill the planting hole would be a good thing to do (and into the surrounding area). This would act as a natural source of nutrients, aiding in establishment.

The exact ratio to use, compost to soil, I cannot prescribe. The general idea would be to use the compost as a soil improver, taking note of the existing quality of the soil and its available organic matter.

Avoid over-use in the planting hole as this could lead to waterlogging. Using the compost as a top dressing after planting and into the future would also be of benefit for adding nutrients and organic matter.

As a fish food

Compost works very well as a fish food – albeit as an indirect one.

There are natural occurring foods in a fish pond which includes tiny plants (algae or phytoplankton) and very small creatures (zooplankton). The algae and zooplankton feed off the nutrients provided by the compost which in turns provides food for fish such as carp and tilapia. You can find more details in the preparation and use of compost

Finally

As you can see, there are many ways you can use compost in the garden. And that’s just at home! Compost has also been used to treat pollution, clean storm water and sequester carbon. Learn more about how compost can be used in 23 Benefits of Compost Backed by Science

Header image of compost (149247638) by © JoycegracewebDreamstime.com