Grower’s Corner – fallow beds and green manures
Green manures are ideal whenever a patch of land is going to be free of crops for six weeks or more, and they are particularly useful to vegetable gardeners and allotment holders for soil improvement, weed suppression and – of course – to make your allotment look ‘productive’ when the allotment officer comes round.
As they grow green manures form a carpet that prevents weeds from growing and some have the ability to absorb nitrogen from the air, which is transferred to the roots and released when dug into the soil, giving a boost to the vegetables that follow. Growing a green manure in winter prevents soil from having nutrients washed away by rain or snow, and some varieties have a fibrous root system that helps to give the soil structure. Clover is a green manure that can be left to grow for a year - when it flowers it attracts bees and other pollinating insects. In addition, green manures, especially autumn sown ones, are effective in mopping up nutrients remaining after crops, preventing them being washed away by rain. Italian ryegrass, and rye sown in September are very hardy, growing all winter before being dug in during spring to release nutrients as they rot. Other benefits of green manures include shelter for beneficial insects such as ground beetles although it should be noted that slug control may be needed after green manuring. Finally, Tagetes minuta is claimed to suppress eelworms and weeds, but only used as a supplement, rather than a replacement for other controls methods.
Growing tips
Prepare the soil by removing weeds, digging over if it hasn't been recently cultivated and raking level. Scatter seeds over the surface of the soil using around 50g of seed per square metre or following suppliers recommendations for specific crops. Make sure the seed is in firm contact with the soil by gently tapping over the surface with the back of a spade. Water in well. Bare patches should be covered within two to three weeks and plants will the most good if they are left for around eight weeks before digging in. If plants start to flower before this, cut off the tops and dig in. Make sure you aren’t planning to go on holiday when your manure crop is likely to flower, or your neighbours will be furious about the seed blown into their plots or gardens! Leave the green manure to decompose in the soil for up to four weeks before growing vegetables.
Seasonal green manures
Mustard - sow from March to September
Crimson clover - sow from April to August
Fenugreek - sow from March to August
Agricultural lupin - sow from March to June
Winter tares - sow from March to September
Winter field beans - sow from September to November
Mustard and clover photographs by rightee and ximenatapia, used under a creative commons attribution licence