Empty Ground & Green Manure

An empty patch of ground will rarely stay empty for long - even the tidiest garden will have weed seeds blowing in from somewhere. Although, I must admit that as a jobbing gardener I'm delighted to have clients who like bare ground around their plants and shrubs because it creates a never-ending job for me! At home I try to have no bare soil at all in the vegetable garden, partly because I just don't have time for endless weeding but more seriously because an exposed soil can easily become a damaged soil. Drying winds or heavy rain can both damage the structure of the soil, can wash nutrients out or even leave the top surface to blow away. Think dust bowl in the US. Just the baking of the sun is enough to render the soil unworkable.

A Small Patch of Bare Soil Between the Zinias & Tomato Frame

But don't worry, this post isn't about mulch again, although of course that is one very good way to protect unused soil, but is about growing what are known as green manures. Broadly speaking, this is a crop which is grown specifically to be turned back into the soil to add organic matter, nutrients and structure. I admit that I've never really been very successful with this aspect of green manuring. Because the cut down and then turned in vegetation rarely seems to break down in time for using the land again, I've opted for a kind of half-way house. Plus, as someone who is trying to practice some form of No Dig gardening, the idea of digging unrotted vegetation into the soil doesn't sit well with me. 

So instead, I cut my green manure down to the ground and simply leave it lying on the surface as a mulch. When I need to use the ground I clear the semi-decayed foliage away to the compost heap. Any remaining roots can be forked out (along with the ubiquitous mole tunnels) and also composted.

Bee on the Phacelia

My green manure of choice is phacelia, a purple-flowered plant beloved of bees and other pollinators. To be honest, I grow it as much for the benefit to insects as its quality as a green manure. Ideally sown in spring or late summer, it is a plant that can be sown at anytime apart from during the winter; it will stand drought and a small amount of frost, although a bitter winter will kill it off. I like to leave it growing and flowering as long as possible, and only cut it back about a month or so before I anticpate needing the patch of ground again.

I currently have a little patch in my brassica bed where we've eaten all the spring cabbages (they lasted into July this year!) in an area that won't be used again until next spring so is a perfect location to sow phacelia. Apart from a block of summer cabbage, the rest of the brassicas are kale and broccoli plants that will be in the ground right through the winter, so it makes sense to just fill in the gaps.

Cleared and Ready to Sow

Sowing is easy: while clearing the few weeds I lightly forked the surface leaving it fairly level. The seeds are scattered across the surface and then gently raked in. I didn't water as we'd just had a lovely twenty-four hours of rain but will do so if the weather returns to a typical hot and sunny August. The seedlings should be up in about ten days or so and hopefully will be dense enough to suppress the majority of weeds. In a few weeks it will be flowering and all being well will do so until into November.

A Vegetable Bed Full of Phacelia Green Manure Last Year

Given that I almost always add compost into the ground when planting out my vegetables I'm happy to use my green matures on the compost heaps rather than the more conventional method of cutting them down and digging them in. There is nothing wrong with trial and error and working out the best methods for you and your garden!