Why organic matter matters for your garden's health

Production of aerobic compost in composting bins. Photo: Dr Muhammad Firdaus Sulaiman/UPM

Organic matter is the foundation of a healthy garden soil. It comprises decomposing plant and animal materials, such as leaves, grass clippings, food scraps and animal wastes.

Organic matter provides a range of advantages, including enhancing soil aeration, boosting the soil’s capacity to retain water and nutrients, strengthening the soil’s resistance to erosion, regulating soil pH, and promoting healthy root development.

Organic matter promotes the growth of beneficial microorganisms like bacteria, fungi and protozoa. As it decomposes, it supplies vital nutrients to plants and contributes carbon, which is absent in synthetic fertilisers.

Carbon is an energy source (or food) for microorganisms, explaining why organic matter enhances soil microbial life.

However, organic matter has certain disadvantages when compared to synthetic fertilisers. Its gradual decomposition in the soil means that nutrients are released at a slower pace, making them less readily available to plants.

Additionally, organic matter often has inconsistent nutrient content (even when taken from identical sources) and lower nutrient concentration.

Agriculturists, therefore, advocate for the combined use of organic matter and synthetic fertilisers, acknowledging the advantages and disadvantages of each. In that way, they compensate for the weaknesses of one with the strengths of the other, leading to enhanced overall benefits.

Making compost is a good way of using food waste. Photo: 123rf.com

There are several ways you can increase organic matter in your garden. Besides using organic fertilisers, you can incorporate organic materials like plant cuttings (stems and leaves) and grass clippings as mulch on the soil surface or compost them. Composting can be performed through two approaches: aerobic composting, which requires oxygen, and anaerobic composting, which does not.

Many methods are available online for both these types of composting, but here is one easy DIY method for aerobic composting:

1. Pick an empty, preferably roofed, garden spot for the compost pile.
2. Collect a 3-to-1 mixture of brown (carbohydrate-rich) and green (nitrogen-rich) materials. Examples of brown materials are dried leaves, small twigs, sawdust, paper, cornstalks and corrugated cardboard. Green materials include fresh grass clippings, eggshells, and vegetable and fruit scraps. Do not add oil, milk or meat into the compost pile.
3. Chop up the materials using a hoe or spade.
4. Thoroughly mix the browns and greens, while spraying water to achieve a moist consistency (just damp, not too wet or dry).
5. Stack the compost into a tall pile (at least 1m x 1m x 1 m).
6. Cover the compost pile to prevent excess water from entering.
7. Every few days, uncover, turn, and moisten the pile, then re-cover. Repeat until the pile no longer heats up (which can take 6 to 8 weeks).

Common beginners’ mistakes with aerobic composting involve over-watering (leading to excessively wet, dripping compost), leaving the compost pile uncovered and exposed to rain, adding excessive or insufficient brown and green materials (incorrect ratio), adding oil, milk, or raw meat that attracts pests, frequently adding fresh materials into the pile, neglecting to regularly turn the compost pile, and maintaining a pile that is too small or excessively dispersed.

One form of anaerobic composting is Bokashi fermentation that offers some benefits over aerobic methods, such as requiring fewer input materials and providing quicker processing times. The following is one method for Bokashi fermentation:

1. Get a Bokashi bucket that has a spigot (faucet) installed near the bottom of the bucket. Alternatively, you can make one out of a 20-litre paint bucket, following the many instructions online.
2. Acquire Effective Microorganisms (EM) as an inoculant for fermentation.
3. Collect and cut kitchen and food wastes, avoiding liquids, large bones or shells, pet wastes, non-decomposable materials, and excessive amounts of oil, nutshells or woody materials.
4. Add food wastes to the bucket, compress to a 3cm layer, and add 2-3 tablespoons of EM. Cover tightly with the lid.
5. Repeat steps 4 and 5 until the bucket is almost full, creating alternating layers of food waste and EM.
6. Leave the bucket tightly closed and undisturbed for at least two weeks before use.

During fermentation, liquid leachate collects at the container’s base. To avoid odours, regularly drain it through the spigot without opening the lid. Use this leachate, also called compost tea or Bokashi tea, as liquid fertiliser, and apply the fermented Bokashi solids to the soil at 200g per square metre.

You can also directly incorporate other organic amendments into your soil, such as peat moss, coir, composted or processed materials like bark and seaweed, animal by-products (for example, bone meal, blood meal, and fish meal), eggshells, and wood chips. Do not, however, add to your soil or compost spent tea leaves or coffee powder, as their caffeine content has been shown to be harmful for plants.

Dr Christopher Teh heads the Dept of Land Management, Faculty of Agriculture at Universiti Putra Malaysia. Dr Muhammad Firdaus Sulaiman is a senior lecturer at the same department.