Trefoil - good for under sowing sweet corn and will fix nitrogen in the soil

Trefoil – good for under sowing sweet corn and will fix nitrogen in the soil

My first article in this series covered the 7 reasons to use green manures – any plants that are grown to benefit the soil. Today I’ll cover where and when to use them.

Vegetable Garden

Green manures can be grown as a ‘catch crop’ – something to fill a gap in the growing plan for any particular border, bed or growing area. For example, after lifting potatoes don’t leave the soil bare but pop in something like Grazing Rye or Winter Tares which can be sown quite late and will keep the soil covered in the winter months.

You can also sow fast growing green manures in areas where you plan to plant frost tender crops such as courgettes or runner beans, while you’re waiting for the weather to warm up. Some green manures will germinate in early spring and will keep the ground free of weeds. A few weeks before you’re ready to put in your frost tender plants dig in the green manure (leaves and roots) and this will be a good source of organic matter for greedy, moisture-loving crops like runner beans. However, don’t do this if you’re planning to sow any small seeded crops like carrots or parsnips as the green manure will inhibit seed germination.

Where you have a tall growing crop such as sweetcorn, you can sow a green manure between the plants to help reduce weed problems. A low growing plant such as Trefoil will keep the ground covered and this can be left to grow over winter once the sweetcorn has been harvested.

If you know your soil has been ‘over worked’ by previous gardeners (say in an allotment) and little bulky organic material has been added, it’s a good idea to grow a green manure in the first season.

Tares

Tares – great for releasing nitrogen quickly in the spring after digging in

Ornamental Garden

A fast maturing green manure can be used to fill bare patches as spring flowers die down but before summer bedding can be planted. Green manures can also be used to revitalise tired soils where old shrubs or roses have been removed and a new planting scheme is planned. The area can be left to recuperate under a green manure for a few months or a year. Attractive green manures can be used to fill gaps around summer bedding or other plants – a low growing variety will help to smother weeds and retain moisture.

Fruit garden

Blackcurrants are ‘greedy feeders’ and can benefit from a green manure which helps to take nitrogen from the air and fixes this in the soil for plants to use. A green manure such as Tares can be grown around the fruit bushes after fruiting and then incorporated into the soil just before the next growing season – just hoeing off the tops in the spring and leaving these to decompose on the surface should do the job.

Winter – hardy green manures can be grown around the bases of fruit trees in the autumn. Helping to keep down weeds these can be cut down and left to decompose in the spring which will once again provide a valuable source of organic material for the tree. A long-term green manure, such as Clover, could also be grown around the tree – this will provide weed cover and also be a rich haven for pest – eating wildlife.

Hungarian Grazing Rye - the best gareen manure for soil improvement, especially on clay soils

Hungarian Grazing Rye – the best green manure for soil improvement, especially on clay soils

My next ‘Green Gold’ article will give some examples of different green manures and their strengths and weaknesses.

Source: ‘Green Manures’- Garden Organic Guide. September 2010

Other articles in this series: Green Gold- 7 reasons to use green manures

Old School Gardener

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