An expert guide to compost

Thames market gardeners Niva and Yotam Kay’s tips on compost.

As you build your compost heap, you will be able to observe how your compost heap “behaves”, and use your observations to fine tune your future piles.

Making your own compost is easy and rewarding. You can use a broad range of materials, depending on what is readily available. The bulk of the compost heap is made with materials that have a varying ratio of carbon to nitrogen. The carbon-rich materials add mass to the heap and are the basis for the organic-matter content, which is the key product of the composting process.

Carbon-rich ingredients include:

• cardboard

• dry leaves (best shredded or mowed over if used in abundance)

• mature cover crops

• mature hay

• mature plant stalks

• nut and seed husks

• sawdust (from untreated wood) • shredded newspaper and office papers (preferably with low number of coloured images)

• woodchips.

The nitrogen-rich materials stimulate microbial growth and the decomposition of the carbonrich materials.

Nitrogen-rich ingredients include:

• food scraps and kitchen waste • grass clippings (with no seed heads)

• coffee grounds

• fish

• manure

• blood

• pine needles

• seaweed

• weeds (with no viable seeds)

• wool

• young hay or cover crops

• urine (not allowed under organic certification).

Composting is a relatively forgiving process, and you don’t need to be precise about the exact carbon-to-nitrogen ratio; it can just be used as a guideline. As you build your compost heaps, you will be able to observe how your compost heap “behaves”, and use your observations to fine tune your future piles.

Compost heaps built with excess carbonaceous materials will take a long time to break down; you can fix this by pouring high nitrogen liquids over the heap, as long as cold winter temperatures aren’t the problem. Compost heaps built with excess nitrogen will smell of ammonia for a few days until the materials stabilise. As you build your pile, pay attention that you create a pile that will encourage aerobic conditions. To facilitate this, avoid compacting layers, and alternate with layers that are made of large particles that have plenty of air gaps.

Mineralising, inoculating and activating amendments to add to your compost include:

• Mature compost which acts as an inoculant at the start of the process, and during the curing stage.

• Garden soil which not only acts as an inoculant but also helps retain nutrients that would otherwise be lost to the atmosphere or leached out with water.

• Wood ash from untreated wood, for increased mineral content; ash must be used very sparingly, no more than a dusting over a few layers because of its strong alkaline pH.

• Small bones or pre-baked and crushed large bones, for increased mineral content, particularly phosphorus.