HOW LONG DOES IT TAKE TO MAKE COMPOST?

Anything from three months to three years!

It depends on what kind of home compost bin you have
What materials you put in
Where you place your bin
How moist and airy your bin is
How much trouble you have taken.
What grade of compost you want to use

The more care you take, the quicker you will get good compost. but you can hurl everything into your compost bin and three years later there will be usable compost at the bottom.

So how do you decide which approach is right for you?

The hotter the bin the faster the composting process.
A covered, plastic bin in a sunny place could get up to 60C in the summer and if you fill it with quick
rotters, leave the contents to decompose without adding fresh material, and turn it once or twice, you may have usable compost after 3 months.
This will be mulching compost - roughish stuff useful for:
putting round shrubs and bushes
putting at the bottom of a planting hole
but too coarse for potting or seed sowing.

If you want to use your compost bin continuously, adding stuff every day or every week, then you cannot
turn it as this will mix up the fresh and partially decomposed materials. In this case make sure that you put in a well balanced mix of compostibles and after 3 months there may, in ideal weather, be a little finished compost at the bottom.
However, it is probably easier to wait for 6 months, over the summer, and then harvest some compost. When you are filling your compost bin over the winter, the material is breaking down slowly, because of the cold, so what you put in in the autumn won’t be ready for use until late the following summer.

Larger bins generate more heat and retain it better so work faster than little bins. If you have a small bin it is especially important to put it somewhere it will get some sun or you will be waiting a couple of years for your compost to be ready.

Turning the contents of your compost bin helps to:
generate heat as it introduces air to the middle of the heap, air needed by the bacteria doing the composting for you. The more often you turn the heap the faster it will work. The downside is that it is hard work and that you have to have another bin for your fresh compostibles while the first is rotting down.

Wooden bins do not retain heat as well as plastic and they often dry out round the edges in hot weather. Dry materials do not break down as those bacteria will only work well on moist stuff. The classic New Zealand box works on a 2 year rotation: fill one side one year, leave for a year while you fill the second side and dig out the finished compost in the spring of the 3rd year.

WASTE THAT SHOULD ROT DOWN QUICKLY, THAT IS IN ABOUT 6 MONTHS:
Annual weeds - chickweed, groundsel, bittercress; include the roots because the soil sticking to them contains lots of useful bacteria
Dead flower heads with thin stems like sweet peas, stems as thick as delphiniums may take a year to completely break down
Fruit peel rots quickly, put orange and lemon peel into a compost bin, it is only the worms in a wormery that do not like it.
Vegetable trimmings like tattie peelings, pea pods and outside leaves break down fast.
Lawn mowings that have not been treated with herbicides break down fast as long as you add no more than 20cm depth at a time. If you have more, layer them with drier, more absorbent material like weeds and stems. (See Too Much Grass for more ideas)
Vegetable plants and leaves like rhubarb leaves, tattie shaws, bean plants and carrot tops
But
Tough material like cabbage and sprout stems take years.
Peach stones and avocado stones last for years in a compost heap

WASTE THAT USUALLY TAKES 1 TO 2 YEARS TO ROT DOWN:
Stems of herbaceous plants that you cut back in the autumn
Soft, green, hedge clippings and prunings; but conifer and other evergreen cuttings will take 3 years or more to completely break down
Nettle and dock stems
Paper and cardboard
Shredded woody prunings
Autumn leaves  But oak and beech leaves may take 3 years

WASTE THAT WILL PROBABLY TAKE 3 YEARS OR MORE TO ROT DOWN:
Softwood sawdust and wood shavings
Ivy and clematis stems
Holly and other evergreen leaves or conifer needles
Woody twigs that have not been shredded
Egg shells, essential to counteract acidity in the heap but slow to completely disappear
Moss in large quantities ie more than a small bucket full
A compost bin full of grass clippings with nothing else layered

The larger the bits you put in the longer they will take to decompose.

A small amount, eg 10%, of slow rotters mixed in to a heap largely composed of quick rotters will disappear but, in general, slow rotters will rot slowly whatever else is in the compost bin. You will be picking twigs out of your otherwise finished compost if you mix woody stuff into a quick bin.

Don’t despair if your compost isn’t ready to use, leave it a bit longer and, in the meantime, get another home compost bin for your fresh compostibles or bag up the semi-rotted compost and use your bin for fresh material.
If you have a small garden and are short of space it is worth trying to make compost as quickly as possible, plenty of heat, a good balance of materials and some turning, so that you can manage with just the one bin.
If you have a large garden you can take the lazy approach and have a row of bins all composting at different rates.

                                          The best compost cannot be produced overnight – it takes time.

Other seasonal tips you might find useful:
Recycle your Christmas decorations and use them in the garden.
Warm up your compost in the spring
Using your compost - make the most of your composting efforts
Making your own compost mixes
Dealing with the Autumn Clearing - shredding and more
Is your compost slimy and smelly? - solve the problem.
Revive your home compost bin in the spring