Topic: green manures

[adrianhumph]

Hi All :D
             I have growing on my allotment 2 different green manures, mustard & alsike clover. Both have done a good job in covering the plots over winter keeping the weeds down particularly the clover it is like a mat ;D Bearing in mind that I want to plant my early spuds in these beds, sometime in mid March, should i be cutting the manures down now & digging them in ? or can i leave them for another month?
                     
                                            adrian

[derbex]

Adrian,

I haven't grown either of these, but from reading around I think you are supposed to leave a few weeks between digging in and sowing. Mind you chitted spuds should be pretty robust so you probably don't need that long.

Jeremy

[philcooper]

There's still a lot of time for rain which will leach the goodness from the soil if you dig in now.
Freshly dug in green manure will inhibit the germination of seeds for 2-3 weeks but plants such as potatoes and those raised in modules are not effected.
So dig the GM in when you plant the spuds to get maximum value from it

Phil

[john_miller]

Certified organic procedures recommend a minimum waiting period of two weeks between incorporating a green manure and planting any crop. If soil temperatures are low then a longer period is recommended.
This period will allow soil bacteria levels sufficent time to build up, which also involves the bacteria using the nutrients themselves for reproductive purposes, so that all the plant material is broken down enough to avoid crops being subject to a flush of high levels of salts, especially nitrogenous ones. To long a period between incorporation and planting could, as Phil mentions, result in excessive leaching of salts by rain. Any overwintered green manure that has to be dug in a long time prior to  planting (as may happen with squashes or tomatoes) should be followed by another green manure until the area is needed.

[swampig]

Green Manure??? sounds good. Ive got a piece of my plot that I may not plant in this year and was thinking of covering with black plastic but this sounds much better. Any advice??

[john_miller]

With an entire growing season for this crop you may want to consider growing a long season legume. If you have really good drainage then you may want to even consider lucerne/alfalfa which will fix a lot of Nitrogen and, because it can send roots into the subsoil if they won't drown, pull up nutrients which you will eventually incorporate into the top soil. The big problem I would see with this on a garden scale is that the roots can grow extremely thick and may be difficult to turn into manually (a tractor and plough can have problems!). Alternatively any vetch or fumitory will fix N or you can use field beans (or pea) and turn them in rather than take a crop from the plants.
Another good summer green manure crop would be buckwheat which, because you can get multiple (well, two) crops in between frosts, can add a lot of organic material to the soil (if you are going to let it flower though I hope you don't mind bees!). Sown thickly enough buckwheat will inhibit annual weeds growing in the summer. Then follow it in the fall with a frost tolerant green manure.

[john_miller]

Oops, for 'fall' read autumn in the U.K.!