Weeds themselves are a reasonable green manure - but they have one problem we know only too well; they don't stop growing when you want them to!   Their roots spread and persist, their seeds get everywhere.

A few more useful green manures - I've **starred** those I have used.

Don't feel constrained to limit yourself to seeds listed here, or in the Green Manure sections of the catalogues.   Many of these have a long history of use in agriculture - so they have proven benefits, but they may need a tractor to dig them in!   You can use any fast growing green cover plants (preferably unrelated to any of your crop families!) which can be easily dug in.   Green manuring is a technique, not a list of plants.

• For sowing in an empty bed
  • The Brassica Family recycle nitrogen rather than losing it.   Remember club-root prevention and your rotation (I don't use them, as I grow brassica crops, and have clubroot in some beds).
    • Mustard - very fast growing surface cover (can be turned in after about three weeks).   Sow after your early potatoes and dig in as or before it flowers. Not suitable for over-wintering.   Mustard sown before your potatoes is said to attract wireworm, feed 'em up, so they fly away before devouring your crop.
    • Fodder radish - deep tap root brings up nutrients from the sub-soil, and lots of organic matter; will over-winter.
  • Legumes - these all fix nitrogen, so they recycle and add nutrients.   Good sown before (or even among?) green crops which are heavy nitrogen users - like brassicas.
    • **Clovers** - too slow growing for the allotment, unless you have the space for a permanent bed - many varieties can be cut, to encourage new growth, like comfrey below.
    • **Fenugreek** - quick-growing, lots of foliage, and easy to dig in; will over-winter if it's mild.   And the leaves are edible - the methi you can buy in Asian grocers.
    • **Alfalfa,** Field Beans, and Agricultural Lupins have deep tap roots which bring up nutrients from deep down.
    • Tares (Vetches) have the same deep tap roots and are very hardy, so good for over-wintering.   But as they decay, they produce toxins to inhibit germination of small seeds; either follow with transplants, onion family sets, or potatoes, or delay sowing for at least a month.
  • Grasses - good for over-wintering, and to prevent rain leaching out nutrients.   They recycle nitrogen, and bring up nutrients from the sub-soil.   They fit anywhere in a rotation.
    • **Hungarian Rye** - grows so many roots so fast, so deep, apparently even in iron-hard clays, that it has earned the title "nature's spade".   Two problems - if left too long, it is supposed to be extremely hard work to dig in.   And, like the tares, it produces toxins to inhibit germination of small seeds - so follow with transplants, onion family sets, or potatoes, or delay sowing.
    • Annual Ryegrass - similar to the Hungarian, but less bulk, and easier to dig in.
  • Others - which will choke out weeds, protect the soil, draw up nutrients from the sub-soil, attract bees or hoverflies, and fit anywhere in a rotation.
    • **Phacelia** - sow by late August or early September to give quick cover. Phacelia is not always winter hardy - but if the frost kills it, simply leave the frozen plants in situ to provide a protective soil cover. Or sow in spring so the flowers attract bees and beneficial insects.
    • **Buckwheat** - quick growing if sown early enough, but if sown in autumn, it's likely to wait until spring to germinate!   Then it becomes a weed - lovely, delicate, useful, but a weed!
    • Try the Poached Egg Plant (Limnanthes douglasii), a hardy annual.
      • Sow it in autumn under your fruit bushes where it will romp away in autumn or spring, flower, and die as the fruit comes ripe.   It will smother weeds well, attract beneficial insects - and then self-seeds, so the process repeats itself the next season.
      • Or as winter cover on your vegetable beds - strip off the growth in spring for the compost heap.
• Edible manures? - just because it's good for the soil doesn't mean you can't eat it too.
  • Claytonia (Miner's Lettuce) and Corn Salad survive all but the hardest winters, and give good ground cover, and are easy to remove or dig in; and they offer a succulent salad into the bargain!
  • I've read of people using Spinach as a green manure - although I suspect it wouldn't survive Yorkshire frosts.
• In a permanent bed, as a useful fertilising crop
  • Comfrey and Nettles
  • I have Borage and nasturtiums growing all over the place - some I leave, some I allow to grow only big enough to add to compost, or to make a "tea"-feed
  • Clovers