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Struggling to decide on the right type of compost? Read our comprehensive Compost Buyer's Guide below for everything you need to know about compost!
What is compost?
Compost is organic material such as bark, garden clippings and cuttings that has been fully decomposed to make a rich soil-like material that is full of nutrients and organisms that are extremely beneficial for growing and sustaining a healthy garden.
What is compost used for?
Compost can be added to garden soil and raised beds to enhance or improve their nutritional quality.
What is compost NOT used for?
Compost is NOT used as a primary fertiliser.
While compost has many essential nutrients for your soil, it can not be used as a standalone fertiliser for your garden because it lacks the micro-nutrients that many plants including edible ones require to grow.
Compost is NOT used as ordinary soil or potting mix.
Compost must be mixed with topsoil and all garden soils to improve their fertility and structure.
However, you don’t use compost instead of soil as it may be too rich on its own. It also lacks the consistency to provide good aeration and support for plants’ root structures.
However when dug in with soil it becomes a perfect growing mix for most plants!
What is in compost?
All composts require a mix of carbon-rich organic materials, nitrogen-rich organic materials, oxygen and water. Ingredients might include: dry leaves, twigs, dead plants, bark etc.
Nitrogen-rich materials (green): grass clippings, animal manures, etc.
When you buy bagged compost (as opposed to making it yourself) it’s worth checking the ingredients as they can vary from brand to brand, the best composts are made to the NZ Composting Standard NZS4454.
What makes compost different from other soils?
Compost vs Topsoil
The difference between topsoil and compost is that compost isn’t actually ‘soil’. It is a blend of natural materials broken down into organic matter rich in nutrients that serve as a natural soil conditioner.
Compost can be added to topsoil to improve its structure, reduce compaction, and improve water retention and drainage.
Unlike ordinary garden soils, high quality manufactured composts have been processed to a point where they do not contain the seeds of weeds.
Compost vs Garden Mix & Vege Mix
Compost is different from garden mix and veggie mix because you don’t plant directly into it.
Most garden mixes are created with a mixture of organic and materials and fertiliser blends, making them more sustainable for plant life.
Compost can only enhance your garden or vege mix, helping improve the texture for the plant roots to grow and easily through the soil.
Compost vs Potting Mix
Compost is different from potting mix in that it cannot promote healthy plant life while in a container or pot.
Potting mix is specially designed to allow for airflow, drainage and fertilisation while a plant grows in a pot.
Don’t use compost as a potting mix substitute: it won’t provide the plant with the right nutrients, airflow and drainage.
Types of compost
All composts, including store-bought, have the same fundamental organic materials. However, the specific ingredients may vary depending on where the compost was made and the specific gardening application it is being marketed for.
Here are some of the more common types of compost.
Standard home-made compost
All of its carbon content and most of its nitrogen content comes from plants (as opposed to manure and other animal products). Think grass clippings, leaves, vegetable scraps etc.
This type of compost is excellent for enhancing garden soil and topsoil but it lacks the concentration of nutrients found in vermicompost and composted manure and it can be difficult to attain the right heat in smaller compost piles as well as control moisture levels.
Without a proper compost process, there’s a risk that weeds can remain in the compost, as well as other diseases from infected plants. Also unpleasant odours can occur if plant material is not properly composted.
Vermicompost
Vermicompost, such as our Revital Grow-All is essentially the composting of waste with the help of earthworms.
The earthworms live and eat the organic material in the compost and their digested waste becomes castings and organic manure that is a valuable source of fertiliser for gardens.
Vermicompost is a good alternative to standard/yard compost as it has a higher concentration of nitrogen, phosphorus and potassium.
Composted manure
Manure compost is usually made from cow, horse or chicken manure. Don’t worry - it doesn’t smell anymore and the heating process removes any pathogens.
Commercially these types of manure can be mixed with other manufactured compost to add a significant nutrient boost due to their high nitrogen content.
All-natural organic compost
Natural or premium organic composts are free from chemicals, with all of the ingredients made from natural or organic sources.
Bagged certified organic compost tends to cost a little more than conventional compost as it is more costly to source organic materials and obtain organic certification.
Storing compost
Storing compost properly is essential to keeping the microorganisms that live in it alive and healthy and to prevent deterioration of its structure.
Short-term compost storage
In pile: If you need to store compost for a few weeks, the easiest way to preserve it is by covering the compost pile with a tarpaulin or plastic sheeting. This will prevent excess moisture from getting in your compost but allow for enough airflow and humidity to keep the microorganisms alive.
Bagged compost should be stored under cover, in your shed, or under the eaves of the house.
Medium-term compost storage
If you need to store the compost for one to two months, we recommend placing it in plastic bags or garbage bags, and storing under cover as above.
Long-term compost storage
For anything more than two months, store it in a pile where it is sheltered from harsh weather conditions and be sure that it stays adequately moist to keep the microorganisms alive.
This means periodic flipping to incorporate oxygen and moisture throughout the pile.
As a general rule of thumb, finished compost should be used within 6 months for maximum value.
Check out the New Zealand Ministry of Health guidelines for handling compost here.
What to look for when buying compost
We’ve been selling compost to New Zealand gardeners for over thirty years so we know a thing or two!
Revital Grow-All Vermicompost
Revital Grow-All Vermicompost brings the worms home to your garden! Our Grow-all vermicompost combines the power of nutrient–rich vermicast (worm castings).
This high quality organic compost and is an all-natural, rich source of biological life for your soil!
Order Online
Revital Organic Compost
Revital Organic Compost is an all-natural brew of premium compost. It is the ultimate way to condition soil organically.
This compost is 100% weed-free and made from garden greenwaste to a high standard. Revital Compost is certified organic by BioGro NZ.
Order OnlineLook for high quality
You need to make sure you are buying the best type of compost for your gardening project.
Colour: A healthy compost will be dark brown in colour.
Smell: All organic materials have completely broken down leaving a mild smell.
Texture: Its texture should be light, crumbly and soil-like (not lumpy or heavy).
How much compost do you need?
As a rule of thumb, Compost should be spread at the rate of between 50 and 100mm over your existing garden soil.
Bagged or Bulk?
Buying compost in bags, or getting a delivery of bulk compost is a matter of convenience and price.
Where there is room to have a pile delivered and dropped on your site, then generally gardeners find they can put it to good use!
Buying bagged compost is an advantage where smaller amounts of compost are required, or the access to the area where the compost is to be used is difficult and bags would work better.
Compost prices
The average price for a cubic metre of commercial compost is $140 - 160 per metre. A 25 litre bag of is priced between $8 and $15 depending on the ingredients/ brand etc.
As a golden rule the difference between a cubic metre of compost and the same volume in $8 bags of compost is around double for the bags.
Frequently asked questions
Why do I need compost?
Garden soils and mixes in raised beds can see depletion of nutrients available to plants over time. Weather events such as heavy rain wash nutrients through the soil and often the soil turns hard or claylike when it stops raining. Adding compost helps rejuvenate the soil and improve plant performance.
Some garden soils can be good for growing plants, however they can vary considerably (even within the same garden) and very few gardeners are lucky enough to have perfect soil. Adding compost or soil conditioner helps to provide the right growing conditions, which will ensure you achieve bigger and healthier results.
Choosing the right compost is the way to get the best out of your plants/fruit/vegetables but the ingredients for composts can vary dramatically. For optimal results it is wise to use a ‘fit for purpose’ compost which has been tailor-made for the job in hand.
What are two negatives of composting?
Drawbacks of composting by-products are cost for site preparation and equipment, the lengthy treatment period, targeting final use of compost product, and environmental issues such as odors and dust. Some investment in equipment and site preparation is required or recommended.
What produce should not be composted?
HIGHLY ACIDIC FOODS Citrus fruit, tomato products and pickled food products can do harm to your compost. High acidity can actually kill the good bacteria that helps break down the material in your compost pile.
What happens if you add too much compost to soil?
Soils with excessive compost applications, particularly manure, tend to develop high concentrations of nutrients such as ammonium, calcium, magnesium, potassium and sodium. These soils can also develop high concentrations of bicarbonates, carbonates and hydroxyls.
Does bagged compost smell?
Premium quality Compost that has been placed in bags should have nothing more than a light odour, not unpleasant and reminiscent of vegetative matter or bark. Any residua; odours dissipate within hours or at most a day in the garden. Is compost better than manure?
We recommend compost over straight manure. High quality compost is created under strictly controlled conditions. Bags of manure may not be subjected to the same production standards. Compost is still a safer choice for nourishing soil that will grow your food.
Is compost better than fertiliser?
Both should be used as integral parts of growing successful plants. Compost keeps the soil healthy, which means plants will likely thrive in your garden. The downside is that compost will release nutrients slowly over time, while a chemical or an organic fertiliser provides a boost and accelerates growth in a shorter period of time.
Does it matter what compost you use?
In general, a good all purpose compost will enhance soils where all types of plants are to be grown. Composts that have ‘value added’ such as gypsum, a soil conditioner, or worm castings, a super charged nutrient, will add just that bit extra in the soil ,if your budget allows. How do I know if my compost is healthy?
Compost is ready, and healthy when it looks, feels and smells like rich, dark earth rather than rotting vegetables. In other words, it should be dark brown, crumbly and smell like earth.
How long does it take for compost to work?
When dug through the soil, the structure will be changed and become more friable. Earthworms like to move through soil that is not too compacted. If you have heavy clay soil, add compost every six months for a couple of years to achieve a better texture for your plants to thrive.
How much compost do I add to my soil? repetition?
As a general rule of measurement for compost, we suggest 4 parts soil to 1 part compost.
What is it called when you mix soil with compost?
Often referred to as conditioning or amending your soil, this is the process of mixing compost through soil to increase its nutrient content.
Can I use bagged compost from last year?
Bagged compost can last well over a year. A good compost will have attracted earthworms and these will go to work on your soil when you add the compost! How do you store bagged compost?
If your compost is in bags, store them where they get some winter sun to keep them warm or store them in a garden shed if you have one.
Does bagged garden soil expire?
You can expect an opened package of compost to deteriorate in nutrient levels in 6 months. However, it is unlikely you will find an expiration date.
How do you use bagged compost?
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 revitalise indoor plants, or spread it on top of the soil on your lawn as a soil amendment
How long to leave compost on soil?
Once compost is mixed in with soil, it can permanently stay in your garden.
Can old compost be revived?
Dry compost can be revived by adding water to it to make it moist. Adding blood and bone or organic fertiliser can hel praise its performance level in the soil.
How long does it take for compost to release nutrients?
When using compost as a fertiliser, be ready for a long wait. Nutrient release from compost happens in years, not weeks or months like inorganic fertilisers. Nutrient release happens very slowly and is usually around 10 to 15 percent of the amount applied in the first year.
Do you put compost before or after soil?
Typically you add compost to soil. Wherever possible, it is best to add compost to the soil before planting new crops.
Does compost add nitrogen to soil?
Adding compost will give your plants a solid dose of nitrogen, but it also offers a tremendous injection of soil life into your garden ecosystem.