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.

More lessons learned from our visit to Charles Dowding's NO-DIG garden

We learned a lot from observing and reflecting on the practices of Charles Dowding in Somerset. As well as being useful on our plots these tips might be helpful for those stakeholders who have gardens at home.

New ground coming into cultivation - the NO-DIG method.

If you have a weedy patch (like a new allotment or neglected area) that you wish to bring into cultivation, rather than put in lots of effort into digging and weeding why not follow Dowding method? First spread a thin layer of spent hops to encourage the worms. [If you can't get spent hops, why not try a mixture of grass cuttings and pondweed?]. Then cover with large sheets of cardboard (from bike shops or supermarkets).  Put a 3 in layer of spent hops on top of the cardboard. Monitor for 6 months and hoe off any weeds that make it through the cardboard

If you began this process in the autumn by late May/June you can plant pre sown plants through the hops and cardboard - plants such as courgettes, squash, pumpkins - to get an autumn harvest.

Following on from this you can monitor for weeds through the next winter. Then the following Spring rake away what is left of the hops and cardboard and put on the compost heap. Pull out any persistent weeds. Cover with a 1in layer of compost and its ready for a normal season of sowing. Again you don't have to dig, just plant in modules grown in the polytunnel.

Weeding in a standard plot - the NO-DIG method

 You need to keep on top of weeds. Ideally take them out when they have just germinated and are small. Dowding does 2-3 "weed strikes" in March and April using a swivel/oscillating hoe in the surface compost, to kill small seedlings.  If you miss them in April pull them up whenever you spot them on your plot. Don't ignore the weeds on your plot even if you are concentrating on a different crop in a different area. You really shouldn't have weeds that are flowering on your plot. If you let them set seed you are building up problems for your team in subsequent years.

Notice the organic matter in the mulch that has been added
and the weed free nature of the soil

Edges - the NO-DIG method

Keeping on top of edges is more work for Dowding than weeding. He has a good sized valley at the edge of the footpath to prevent the bindweed and couch grass creeping in from the path. He trims the edges every 3-4 weeks with long handled shears and removes the clippings. Adjacent to his polytunnels he has an edge about 50 cm away from the polytunnel and keeps it clear of weed by growing quick growing lettuce or radish there to ensure that he is weeding these areas and preventing couch and bindweed getting into the polytunnel.

Notice how Dowding clears the weeds and grass from the edges of his polytunnel and keep the weeds down by growing quick maturing vegetables

Pests -- the NO-DIG method

According to Dowding slugs like rotting brassica leaves because they contain a form of alcohol. (That is why beer traps work!). Minimise slug habitat by keeping path edges short and neat and removing lower leaves of brassicas before they yellow. Dowding claims that alcohol is a by-product of anaerobic fermentation which develops when organic matter breaks down in the fairly anaerobic conditions of dug soils. He claims that no dig helps reduce the amount of alcohol in the soil (which is what the slugs like) because all the organic matter breaks down on the surface where there is more oxygen and none is dug into the soil.

By removing the older leaves from the Cavolo Nero there is nothing breaking down which would provide alcohol for slugs and so they are almost absent from no-dig beds

Please let all of us know if you are going to try any of these NO-DIG methods on your plot.