Secrets of composting for healthy soil

Compost can offer a particularly useful boost to plant health in the UAE, where soil quality is often poor. We attend a soil-composting workshop and offer some DIY tips.

Composting can improve the quality of the soil, and consequently the health of the plant.

Most soil will benefit from a little compost, but it is especially significant for the UAE's sandy soil, where the addition of compost is a big step towards ­optimising growing conditions and sustaining non-indigenous plant life.

Compost is simply organic matter, usually green waste (plant cuttings, fruit peelings or vegetable leftovers) that has been dampened down and left to decompose over several weeks or months. The addition of organic matter to pots and planting beds helps condition the soil, assists with moisture retention and provides valuable nutrients to hungry plants.

The new Urban Garden at Time Hotels in Tecom, which is cared for by Slow Food Dubai volunteers, has had the benefit of regular infusions of organic compost materials, which are either dug through the beds or left on the soil’s surface to support the vegetables and herbs planted at the site. In just a few short months, a worm was spotted, then another, and then several, evidence that the soil there has gradually become a living, breathing thing. The plants are thriving as a result.

At Al Barari, the UAE’s largest nursery, Green Works, retains its green plant waste and has vast heaps of organic matter that it recycles back into the soil. Continuing this initiative, RHS Chelsea Flower Show medal winner and landscape designer Kamelia Bin Zaal has introduced composting to the Abu Dhabi island resort of Nurai, where she has recently under­taken a programme of replanting. Bin Zaal believes that composting is key for the sustainability of the lush landscaping design that is an important feature of the island’s luxury resort.

A farm visit to Organic Oasis in Al Khawaneej, Dubai, presented more low-key composting in action after its watermelon harvest, as spent leaves and stems were left in situ to partially decompose before being ploughed back into the soil to support the next wave of planting.

The UAE’s urban gardeners can purchase bags of compost from a variety of garden centres. Warsan in Dubai, in particular, sells a good imported organic compost. However, Laura Allais-Maré, head of the Dubai chapter of Slow Food, is encouraging local organic gardeners to try their hand at domestic composting by recycling their green household waste before it hits the dustbin. She demonstrated some basic composting principles and highlighted the dos and don’ts at a recent gardening workshop at Organic Foods & Café in The Village Mall in Jumeirah, Dubai.

Open-garden compost heaps can harbour vermin and become smelly and messy, especially if left to cook in the sun, so an alternative off-the-peg composting solution for the UAE balcony or urban gardener is a Bokashi bin (available at garden centres, as well as online at www.bokashidubai.com). This provides a sealed and contained vessel for the safe and largely odour-free composting of garden and kitchen waste. Retailing at about Dh280 for a 20-litre bin, it contains a "sieve", lid and tap, and should be used in conjunction with Bokashi bran (currently retailing at Dh80 to Dh90 per 1kg to 2kg bag). The bran composite is either wheat husks or sawdust of other ­fibrous sources, impregnated with ­microbes, which help to get the composting process under way.

Allais-Maré suggests keeping an old plastic container handy in the kitchen to collect waste before transferring to a larger outside bin. Add to the bin a few handfuls of Bokashi bran, replace the lid, and your composting is under way.

Allais-Maré emphasised a few common-sense caveats to local container composting that are particularly pertinent when temperatures climb high and ­microbes and pathogens can potentially thrive in a damp and warm environment.

It is recommended that you keep your bin in a shaded corner of your terrace or balcony, where possible. It is also strongly recommended that composters not add any animal by-products, such as meat and bones, to the composting bins, and stick to green waste only. Cooked vegetables are permitted, but be aware of those that might have been mixed with meat pieces.

Allais-Maré continues: “It will make a lot of ‘wet’ and it will ooze juice. Caution should be exercised as the decomposing matter will contain microbes and bacteria, as well as useful nutrients for your soil. So handle with care and avoid getting the liquid on your skin; using gloves is a good precaution. Remember, our ­ambient temperatures can cook the compost and raise some pretty unpleasant bugs in the process, which is why it can get so smelly.”

After a couple of weeks, your Bokashi box will generate liquid, which can be drained off and collected via its tap. This tea is packed with nutrients, but should be diluted before it is added to the soil. Since the liquid is so concentrated, it is recommended that it be used at a ratio of between 1 to 10 parts compost tea to 100 parts water. Otherwise, it can burn the roots of your plants.

Add a teaspoon of hydrogen peroxide to the liquid to keep unwanted pathogens in check. Wait one minute and then add to the soil around your plants (not the plants themselves). The liquid will keep for a few days in a sealed container in the fridge if you are not ready to apply it all at once.

In addition, the resulting decomposing vegetable matter can be buried in a hole in the garden, where it will further decompose in a contained environment. In a few weeks, either plant directly into that area or dig up the compost and place in other areas of the garden for enhanced soil quality. By this stage it will have lost its unpleasant smell – one gardener at the Slow Food workshop described the resulting material as “a kind of paste”.

Gardeners are reminded that compost is not a mineral product and will not contain sufficient levels of nitrogen, potassium or phosphorus to maintain a healthy garden. The gardener will still have to supplement their soil in other ways to ensure the correct level of nutrients.

Home composting is literally grass-roots recycling; it can become addictive and your tomatoes will love you for it.

Make your own compost

Laura Allais-Maré, head of the Dubai chapter of Slow Food, offers her own budget-friendly home-composting method. The addition of sweet red sand (available from garden centres and plant markets) provides for improved soil mineral content.

• You’ll need two plastic buckets with graduated sides. One should be placed inside the other, to create a sealed well between the two into which liquid can run off and be stored. Holes should be drilled into the sides of the inside/top bucket – about halfway down in a ring – as well as at its base (mirroring the Bokashi sieve design). This allows for aeration of the compost, as well as the drain-off of resulting liquid during the decomposition process.

• Add a two-inch layer of sweet red sand to the base of the top bucket, then add your green waste. It is recommended that no animal by-products are used. With garden waste, avoid any offcuts from deceased or toxic plants, such as oleander. It’s also best to avoid plants that are in seed, as if these don’t fully decompose they may later germinate in other areas of the garden and form weeds. Conversely, don’t include offcuts treated with pesticides or weed killers as these chemicals will be retained in the final mix and may adversely effect the growth of plants where it is applied. Add a further layer – about an inch – of sand to seal in your green layer, and help to keep the flies out. Add a lid to the bucket and your composting is under way.

• Continue with the layers, green matter (two or three inches), an inch of sweet red sand, green matter, and so on. You can also add ripped-up newspaper or cardboard to the green matter (remember it was once trees), which will support the decomposition and also offset the wetness and stop the matter from becoming too sludgy. In the interim, you will also have access to the compost tea at the base of bucket one as it drains out from the top compost bucket.

• When the bucket is full, cover the top with two inches of sweet red sand, fix the lid and forget about it for two or three months. Once the waste has matured, it will have all the nutrients your garden needs.

• The process can be replicated in a single terracotta pot, without a drainage hole and with a lid. The terracotta will absorb moisture as the composting takes place, and when the process is complete, the pot is immediately ready to plant into directly. At this point, a drainage hole will need to be created, to facilitate watering. Large terracotta pots can be bought from vendors on the road to Hatta.