Home Page

Plant Doctor Archive

Adding horse and cow manure to composts

I was very interested in your article on composts. I live on a dairy farm at Pukehina and what I would like to know is how long do you leave a compost heap before it is considered good enough to use in the garden? I have also heard that it is good to soak cow and horse manure for about three weeks as this kills the seeds in the manure. What ratio of cow manure should I use to water?


Compost is ready anywhere from two to six weeks depending upon how warm it is and how you make your compost. Horse and cow manure can only be used when it has composted for several weeks as it will burn plants if used fresh. Soaking it in water for several weeks helps to dilute it — it is up to you how much you use. As long as it is liquid, you can use it.

How to make compost

There is no set recipe when making compost — but there are living micro-organisms involved. When these organisms are provided with ideal conditions and they do most of the work.

Choose an area approximately 1 metre by 1 metre, sheltered from the sun, wind, and rain. The soil should be well drained. The compost bin needs to be well covered so pests will not become a problem. Choose a compost bin that suits your situation. There are many reasonably priced plastic or wooden compost bins on the market.

Lightly fork over the area the bin is to be situated. Add chopped-up coarse garden material which improves aeration and drainage. Air and moisture are very important for the micro-organisms to break down the organic material. If there is not enough moisture, water will need to be added, but care must be taken not to over-water. If there is too much water, the compost will be sloppy, smelly and will compact down.

Build up the compost in layers. The bottom layer is coarse garden material followed by a layer of vegetable peelings, grass clippings or plant material. Sprinkle each layer with "Compost Maker". This helps speed up the decomposition process, increasing the heat generated within the compost heap. Add a 1-2 cm layer of soil on top of this. Repeat the process until the heap is about 1 metre high.

After about two weeks the heap will cool down. Turn the compost over to increase the aeration and speed up the composting process. Place the outside material towards the middle of the heap. Water can be added if the compost is dry. The turning process is made much easier if there are two compost bins to transfer compost from one bin to the other. The heap can be turned in another two weeks. Turning is not absolutely necessary, but when the heap is not turned, the compost on the outer edges does not decompose properly. Incompletely decomposed material should not be used on the garden, but can be cut away with a spade and kept separately for later use when starting a new heap.

Depending upon the time of year, compost can be ready any time from two months to five — in summer the process is much more rapid than in winter. The compost heap is ready to use when it cools down completely and does not get hot after turning over. If the compost still has heat in it and is applied to the garden, it can do irreparable damage to young plants.

Your compost should be crumbly, dark brown to black in colour, with a pleasant earthy musty smell. Spread it around flowering plants, vegetables, ornamental shrubs and roses, working it into the soil.

Only use material from healthy plants in the compost heap. Diseased material and invasive plants like dock seed heads, dandelion roots, couch, and oxalis should not be used as they may survive the composting process to re-establish in the garden later. Avoid putting rose prunings in the compost, they should be burnt instead to prevent the spread of fungus diseases.

If all of this sounds like hard work, or you don't generate enough waste to justify allocating a corner of the garden to a compost heap, there is always bagged compost available at your local garden centre. It is recycled waste from transfer stations in your local area. You will still be helping the recycling cause!

UnitecAdvice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

Reproduced with permission from NZOOM Home and Garden content,
from the previous website of  TVNZ News

The views expressed here are not necessarily those of the RNZIH

Home | Journal | Newsletter | Conferences
Awards | Join RNZIH | RNZIH Directory | Links

© 2000–2022 Royal New Zealand Institute of Horticulture
Last updated: June 27, 2005