Green Fertiliser

Using Green Manure in #WinsfordGardens a #CTWW weekly challenge

As an alternative to chemical fertilisers, green manure can be used to improve and protect the soil. It is therefore, a staple of organic gardening and sustainable agriculture. In Winsford Gardens in Penge, we tried this last year in the two new flower beds we created where our willow arch had stood before it was vandalised. If I recall correctly, we used Fenugreek (Trigonella foenum-graecum.) Fenugreek is a legume (Fabaceae family) and other legumes are the most commonly used green fertilisers because most of them have symbiotic Nitrogen-fixing bacteria in structures called root nodules, and because Nitrogen is the most limiting nutrient in the soil. However, a number of late-flowering non-leguminous plants can also be used. The Fenugreek was allowed to grow for a period, and then before it reached full maturity and flowered, it was ploughed back under the soil by hoeing. In a similar process to composting, heterotrophic bacteria break down the organic material. The Nitrogen becomes available to other plants, but the weak acids also react with insoluble soil minerals to release Phosphates. We have just planted up the two beds so we’ll let you know if it worked.

A couple of years ago we also planted Comfrey in Winsford Gardens and used the leaves to make a green fertiliser. Comfrey (Symphytum officinale) is a perennial herb (Boraginaceae family) with black, turnip-like roots and large, hairy broad leaves that bears small bell-shaped flowers in a variety of colours. It is a fast growing plant and Nitrogen hungry, and the leaves can be harvested up to five times in a single year, after which the plant will rapidly regrow. The leaves and stems are covered in fine hairs that irritate the skin, so they must be cut wearing gloves. ‘Comfrey Tea’ can be made when the leaves are soaked in rainwater for four to five weeks, where they quickly break down into a thick black liquid. Alternatively, they can be used sparingly in the compost heap as a compost activator. In addition to the Nitrogen, the leaves are an excellent source of Potassium (up to three times more than animal manure) which the plant takes from deep in the subsoil, unavailable to other plants. The Comfrey Tea is very strong and must be diluted before use on beds.