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Grant Douglas's Garden Diary

Week 16: Fourth week of April

Two-bin Composting: (Note, you can print this article by clicking on the printer icon on the top right corner of this page.)

There's a good article on Motueka Online by David Armstrong worth reading. I agree with him that you can get too hung up about proportions of carbon/nitrogen in successful composting, but the principal still remains the same, that you need a combination of the two for it to work. Fill up your bin with autumn leaves, or straw and nothing much will happen (both of these have lost their nitrogen content). Here is how I work a two-bin system:

I have two bins side by side. Mine are made of corregated iron and sheep netting for the front. You can use any material that is not going to rot away too quickly, and I find that corrugated iron from the recycling centre is easy for construction and cheap.

The dimensions of each of my bins is 1 metre x 1.5 metres x 1.5 metres high. If you can fill these bins every 6 to 8 months, you should be self-sufficient in compost for the average home-vege garden.

I start filling one of the bins with whatever material I have on hand e.g. garden weeds (not oxalis as temperatures will not get high enough to kill it), garden refuse such as crop residues, lawn clippings, kitchen scraps, old potting mix (whatever organic material I have on hand). I try and mix these materials as much as possible so no layer is particularly thick, especially high nitrogen material such as grass clippings.

I very seldom need to add water as most of the material that I add is green or fresh and so is already high in moisture content, but if you decide to add a lot of hay or straw or sawdust, you may need to add some moisture. But nothing kills a compost quicker than it being overwet, or completely dry.

The material added to the compost peferably should be small in size, so that such things as brassica or corn stalks can be chopped up using a sharp spade or loppers, or shredded, if you have a shredder. Extra nitrogen, if you're short of it can be added by buying in manures or blood and bone, and added every 30cm or so, but no need to overdo it. As you're adding to the heap ensure that the material is moderately compacted especially round the edges.

Over a period of time, depending on how much material you have, the bin will become full to the top. Mine takes about 6 months. When it's full I start turning the top into the neighbouring bin until I get down to a level where the material is sufficiently rotted down to be useful in the garden - I find that this is usually about two-thirds of the bin, i.e. one third of the bin has not rotted down and so has been turned over to the next bin. I can start using this material while adding fresh material to the other bin and away we go again .....

You will find the process will become quicker as the microbes and organisms become more established in the area where the bins are built, but I have never found it necessary to use any sort of activators to initiate decompostion.

Covering the bin is important and ideally a lid to keep excessive rain out, while allowing the heap to breathe is ideal. Other notes are burying kitchen scraps within the heap rather than layering them on top, do not add wood ashes, unless as a very light dusting and don't forget that lots of insects help break down your organic matter, not just worms, but also those little white mites, slaters and beetles.

I could go on for pages but I hope this is of some help in enabling you to turn your kitchen and garden waste into a useful material to increase your garden's fertility.

Broad beans: Some planting schedules recommend the sowing of broad beans at this time of year. I personally would recommend that you hold off a bit longer. If you plant them now they will grow well and will flower, but will not set beans lower down on the plants as there will be not enough bumble bees around to pollinate them (bees cannot pollinate them) and so you will end up with very tall plants, that are prone to wind blow with the bottom of the plants not producing beans.

Sowing or Planting this week:
Brassicas - Cauli, Cabbage, Broccoli, Broccoflower, Brocoflower (remember to choose Spring varieties of these brassicas eg Wintercross or Flower of Spring Cabbage, Snowmarch Cauliflower
Garlic
Lettuce
Parsley
Perpetual Spinach (Plants only)
Silverbeet (Plants only)
Spinach (winter varieties eg. Hybrid No.7)
Spring Onions

Sow Direct:
Chinese Cabbage and other Chinese Greens
Corn Salad
Mescalin Mix
Radish
Rocket