After deciding between growing nitrogen and growing organic matter, the other main factor to consider when choosing cover crops for a no-till garden is—how will you ensure your cover crop doesn't keep growing as a weed and outcompete your vegetables?  While you can dig up cover crops or till them in if you're desperate, it's better to choose crops that are easy to kill without disturbing the ground.

In the summer, mowing is the best way to kill cover crops in a no-till garden.  Only a few cover crops are easily mow-killed, and even with those that mow-kill well, you'll want to plan your garden season so you can allow the crops to reach full bloom (but not set seed) before cutting them down.  Depending on the size of your garden, you may use a lawnmower or a scythe to do the mowing, or might simply yank up handfuls then lay the roots on top of the leaves on a sunny day.  The latter method is actually my favorite with buckwheat in the summer garden since I can often pull up a bed of buckwheat by hand in the same amount of time it would take to put the blade on my scythe or to get the gas mower started.

My other favorite method of killing cover crops in a no-till garden is to let winter do the work for me.  Here's where those of you gardening much further north or south than my zone-6 garden will have to do some experimenting (although Managing Cover Crops Profitably does provide zone-related tips on where certain crops will winter-kill).  When I plant oilseed radishes and oats in the fall, cold weather naturally wipes out nearly all the plants during the winter, producing a mulch that rots into the soil by early spring (for oilseed radishes) or by early summer (for oats).  Homegrown Humus provides planting dates for those of you who want to experiment with winter-killing.

Although mow-killing and winter-killing are my favorite ways to kill cover crops, it's worth having a couple of other techniques up your sleeve in case your experiments don't go as planned.  A kill mulch is an easy way to kill just about any plants as long as you have a month or two to wait before planting the next crop.  Simply mow your cover crops as close to the ground as you can, lay down corrugated cardboard (being sure to overlap the edges by at least four inches so plants can't sneak up between layers), then top it all off with straw (or another vegetable-garden-appropriate mulch).  Lack of sunlight will kill all but the most ornery plants in short order, at which point you can either cut holes in the cardboard to plant directly into the soil, or can move the cardboard to kill mulch a new garden area.

If you don't have time to kill mulch and you really need to get rid of those cover crops, you'll be forced to pull them up by the roots.  I actually use this method often with buckwheat, which is very simple to tear out of the soil, but weeding out most other cover crops will be a lesson in patience.  Good planning ensures you won't need to pull up cover crops by hand very often.