Green manures are an ideal mulch for covering bare patches of soil in the veg garden. The term green manure is frankly a bit misleading because although it’s green it isn’t a manure. “Green” refers to the plants that it comprises, but unlike every kind of manure I know, it doesn’t feed the soil by adding nutrients.

So what does green manure do and why am I recommending it? Green manure conserves the nutrients already in the soil by absorbing them while growing. They are then dug into the ground, thereby returning the goodness to the earth.

Green manures also act as a living overcoat, so like other mulches they stop heavy rain compacting the ground. The soil underneath is always light and crumbly, while unprotected ground is dense and compacted. Plant root systems also bind surrounding soil particles together, so prevent erosion.

A recent UK government report estimated that 2.2 million tonnes of soil are lost every year, so it’s vital we keep our garden soil where it is.

Green manures germinate and grow quickly and there are varieties to suit different times of year. Hungarian grazing rye and vetch, or tares, are the ones to use over winter and how you treat them is much the same as other varieties.

In my book, Hungarian grazing rye is the best option.

Sow it any time in September in most of Scotland, but in higher or more northerly parts of the country, it might be safer to get seed in the ground during the first fortnight.

Choose vetch for sites where you can let it grow away until late the following spring; like all other peas and beans it fixes nitrogen in nodules on the roots.

This makes it the ideal cover for mid-summer sites for courgettes or squashes.

For both plants, rake the ground and broadcast the seed, tamping down and watering. Grazing rye grows to 30-40cm by early spring, when it should be dug into the ground. I find it’s easiest to strim the plants and let them wilt before digging in.

They have an extensive root system, so digging is essential, I’m afraid.

The good or bad effect of grazing rye is that it releases biochemicals in a process called allelopathy. This prevents other plants from germinating and growing well. It persists for 4-6 weeks after the plants are dug in, so only use grazing rye for later plantings like brassicas and leeks, but not catch crops or carrots.

Green manure seed is an annual cost, but tiny compared to many mulches and you could leave a few plants to grow on and collect your own seed.

Plant of the week

Dahlia ‘Ian Hislop’ has warm, apricot coloured single flowers that are attractive to late flying pollinators. The plants have green leaves that stay looking fresh when other plants are succumbing to September dullness. Not winter hardy, the tubers will either need to be lifted and stored or, in a sheltered spot, heavily mulched. But beware slugs in spring.