Grow bag cultivation, a method popular among urban gardeners, is considered to be an ideal system for rooftop farming. It is not only space-efficient, but also ensures there is enough space for root growth and air circulation.
However, while placing these bags on the terrace, along with light-weight potting mixes, a layer of red soil or topsoil must be added to provide weight. Otherwise, if there are strong winds, these can blow over.
“With terrace gardening picking up among most urban families, the use of topsoil and red soil has increased. This leads to exploitation and erosion of the fertile layer,” says John Sherry, the assistant director of Agriculture Farm Innovation Bureau, Ernakulam, Kerala.
He has not only identified this problem, but has also found a solution to prevent further exploitation by innovating a soilless potting mix using rice husk.
In an interview with The Better India, John shares how to make this potting mix and how he grows 30 varieties of vegetables on his terrace with the same.
In April 2020, when John had extra time owing to the COVID-19 lockdown, he decided to take up terrace gardening in grow bags. However, he did not want to add red soil to the mix. So, he experimented with a by-produce of rice, the husk, which is usually discarded as waste.
“Sometimes, to get rid of the husk, farmers burn it,” says John, adding that he decided to use rice husk owing to its chemical composition, which is high in silica, carbon, calcium, and magnesium.
The husk not only offers sturdiness to the bag, but it also keeps the mix well-ventilated and pest-free which in turn offers a good yield. Today, on his 140 sq-ft terrace, John grows 30 types of vegetables including tomato, cowpea, bhindi, bitter gourd, snake gourd, chillies, brinjal and more.
“The method is very effective as it utilizes maximum sunlight on the rooftop and causes no harm to the concrete terrace or house because it is lightweight,” says John.
If you wish to make this potting mix at home to grow your plants, here is the step-by-step process.
How to make the potting mix
You will need cow dung powder, coir pith compost, rice husk, and rice husk ash.
Step 1: Prepare a mix of rice husk and rice husk ash in a ratio of 1:1.
Step 2: In a grow bag, first add a layer of the rice husk mixture.
Step 3: Then add a layer of the coir pith compost.
Step 4: Again, add a layer of rice husk mixture.
Step 5: Top this with four inches of dried cow dung powder.
Step 6: Repeat the layering until 3/4th of the bag is filled.
The filled grow bags are kept in plastic trays that collect water. This is absorbed when the water content in the potting mix is low.
To add nutrition to the potting mix, John advises preparing a 10-litre solution with cow dung diluted with water in a 1:10 proportion. Add 50 grams of potash to the solution and feed it every Monday to the grow bags.