How to reuse spent compost / RHS Gardening (2024)

FAQs

How to reuse spent compost / RHS Gardening? ›

Mulch your beds and borders to lock-in moisture and suppress weeds. Use a shovel to pile the compost onto your beds and a metal rake to spread it over the soil to a depth of around 7.5cm (3in). Over time the mulch will be worked in by soil organisms, thereby improving the structure and health of your soil.

Add brown and green carbon and nitrogen-source material to the pile. In general, add three-parts carbon material to one-part nitrogen. Bhalsod recommends adding three buckets of brown material to every bucket of greens you add. Some carbon sources include dry leaves, straw, pine needles, and sawdust.

You can reuse the same compost over and over for years but use it for mulching only or as a soil conditioner if plants show any signs of disease. Seed composts are very fine and contain very little by way of nutrients.

Benefits of Using Your Finished Compost

You can add compost to your flower and vegetable beds, window boxes, and container gardens; incorporate it into tree beds; mix it with potting soil for indoor plants; or spread it on top of the soil in your yard. Compost can be used as a soil amendment or as a mulch.

Finished or unfinished compost can be applied as a mulch 3-4 inches thick on the soil surface. Do not incorporate into the soil. Keep compost mulch 2-3 inches away from plant stems. Nutrients will filter into soil, without robbing nitrogen from the root zone.

Tip out spent compost, remove any large sections of root and work it back to a smooth, fluffy texture with your hands. Then add handfuls of organic matter, like garden compost or well-rotted manure, to create a mixture of around 70% spent compost to 30% new organic matter.

Human urine is an interesting (and free) compost activator if you're game. It's loaded with nitrogen, minerals, and vitamins, making it a dandy activator. Of course, the easiest way to activate a new compost pile is to take a coffee can full of previously made compost and toss it into the new one. Presto!

Ideally you then cut the old compost with some new stuff, 50:50, and add a good handful of slow-release fertiliser, mix it well and then place back into the pot, ready for it to be planted up.

If too much compost is added to the soil, nutrients including phosphorus and potassium can leach past the root zone and move beyond your garden. The nutrients may leach into surface and ground water from rain or irrigation. Nutrients in surface water supports algae growth and low-oxygen water.

Decomposition will be complete anywhere from two weeks to two years depending on the materials used, the size of the pile, and how often it is turned.

What are 3 things you shouldn't compost? ›

Composting Don'ts

Don't add fish, meat, dairy products, bones, baked goods, fatty foods or grease to your compost pile. These food scraps do not easily decompose and may attract animals. Don't use diseased plants or plants that are toxic to other plants.

There are various ways to use your finished compost. You can sprinkle compost on top or mix it into your flower and vegetable beds, gently rake compost into tree beds, blend it with potting soil to revitalize indoor plants, or spread it on top of the soil on your lawn as a soil amendment.

You can also trench compost one hole at a time. Just dig a hole in a vacant space in the garden, toss in the materials, mix and cover with soil.

When using finished compost you can either apply a few inches of compost on top of the soil, or repot the plant in a mix of 30% finished compost and 70% your usual soil mixture. DON'T use too much compost.

The addition of material that is nitrogen-rich, like coffee, manure, or fresh cut grass, will heat your pile right back up as the thermophiles go to work. Compost thermometers are great ways to tell which stage of decomposition your compost pile is at.

If your pile is not getting hot enough, you will need to add some nitrogen rich products such as garden waste, coffee grounds, or grass clippings. If the compost is getting too hot, you can add some high carbon scraps such as shredded cardboard, sawdust, or straw mulch.

Old compost may have run out of nutrients, but it is far from useless when it comes to feeding your plants. If you use old compost as a mulch on your garden beds it will add organic matter to your soil. Organic matter will help to feed the life in the soil, which in turn will help to release nutrients to your plants.

The short answer is that composted organic matter does not go bad unless you store it improperly. It does, however, continue to break down, and that's completely normal.