All About Soil

Share information about your soils, ask questions about your soil

Soil is the essential ingredient at the heart of our food systems, our ecosystems, and even human health. It is a threatened resource, vital to our future. The EU and UN recognise a number of key threats to soil and soil biodiversity, including compaction, salinisation, and loss of organic matter.

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I use no dig compost in raised beds and on no dig beds. Recently on an organic gardening course we were told that alliums particularly onions and leeks don't like growing in compost and prefer soil that has not been improved. Is this because there is not enough nutrition in compost?

That's interesting. I was going to make a raised bed as I have solids from my bokashi to use and currently nowhere to dig a hole to put them in. I.e. I was going to cover the solids in compost rather than soil. Then I was going to plant up with garlic in the autumn.

Anyway, I may still do this as an experiment, in light of your post, Julie. My guess is that soil will have a different range of nutrients, plus life that is missing from compost. I wonder also if the soil-compost comparison depends on the type of soil?

According to Elaine Ingham, the soil scientist, compost is an innoculant. It innoculates the soil with soil microbes that have fed on the raw material put into the compost bin and in doing so transformed it into nutrients for the soil and in particular biomass which is important for the aeration of soil to allow myccorhizal fungi and aerobic bacteria to live in the soil and feed the plants. The biomass is also important for drainage. But, she says the compost then contains no further nutrients to feed the microbes. So, the compost should be spread on soil to innoculate it with microbial life and then we need to keep mulching to continue providing food for the microbes. So, she's saying that the microbial life in the compost is the densest. Onions produce anti-microbial chemicals, and maybe they don't like compost rich soil because it is rich in microbes and is therefore obliged to produce too many anti-microbial chemicals. Maybe! I will investigate this further. Thank you very much for posting this.

Great to see you all talking this through, Julie, Helen and Jacqueline. It would be good to hear about your results when you have done the mulching/compost experiment.