Using green cover crops

Having been so stimulated by our visit to Charles Dowding's no dig garden, a visit to the student gardens at Kew botanical gardens and a discussion with an organic farmer at the Alresford show, all within the space of a week, we have decided to try a little experiment  with four green cover crops or manures this autumn at Highbridge Community Farm.

These beds are 6ft (180 cm) wide with a 1 ft (30 cm) path of wood chip between the beds. Each bed has been sown with a different  cover crop 

Ideally a green cover crop for winter use must germinate in the late summer or early autumn after a crop has been removed, grow as much as possible during the autumn, covering the ground to suppress other weeds from growing, and then provide biomass for later composting. The leaves reduce soil erosion from run off and wind. The roots of the green manure plants bind the soil together, feed the mycorrhiza, and draw up nutrients which otherwise might be leached deeper into the soil by the rains. Ideally too, a green manure should be cheap to buy and, for economy, it should set seed that's easy to save. Then the plants should be killed off by the frosts of winter.

At Kew botanical gardens they sow Phacelia (Phacelia tanacetifolia) in beds during spring where tender plants like courgettes and squashes will be planted in June. The purple flowers attract beneficial insects, such as hoverflies whose larvae eat aphids. However Phacelia can be sown up to September, so we are going to try some this autumn. As Kew use a no dig system they either hoe or pull out the plants when they are ready for the next planting. All the biomass goes into the compost. If we have a strong frost they may die, but failing that we will pull them out just before we sow the next crop and compost the biomass. They should keep the weeds down during the winter.

We spoke to an Organic farmer at the Alresford show who has been planting green manures for 20 years. He recommends Daikon Radish to plant from June -September as it matures in 60-70 days. It dies off in frost. It produces a large leafy rosette and a long white taproot up to 20 cm long but has longer fine root hairs which pull nutrients up from maybe a metre below the surface. You can eat the leaves and the roots. The roots make long deep holes ideal for drainage. If the roots are left in the ground after the leaves have died they will rot over the winter and the nutrients from deeper down will be released in the surface layers

Bob Flowerdew (from Gardeners question time) recommends Claytonia (Montia perfoliata). It is sometimes called Miner’s Lettuce or Purslane. It is a low growing ground covering salad plant  It thrives in cool and damp conditions where it may grow  so densely that it excludes all else, yet it seldom becomes a problem for it dislikes hot dry conditions. Soon there should be a lush green carpet which could survive mild winter frosts but would disappear by early summer. It is remarkably easy to weed out with a wolf hoe.  You can either incorporate it in situ by hoeing it under or very easily strip it off to compost the plants as extra biomass. Either way Claytonia improves the soil leaving a fibrous matt of tiny rootlets which soon decay.

The Poached egg plant, (Limnanthes douglassii), has long been recommended as a good attractant for beneficial insects. It dies down naturally in summer leaving the soil bare, after a raking. However on vegetable beds you can strip it away and compost it incredibly easily leaving the soil bound with a mass of fine roots which do not regrow. Or you can cover it with an opaque plastic sheet and it rots down incredibly quickly in situ. You can even tear out patches to plant through.

Additional beds have been covered with mulches of organic matter- this one covered with pond weed Elodea from the pond the other side of the track past the cars.