what cover crops for orchard in northern climate

Does anyone has an experience what kind of cover crops to use in the orchard? I would like to limit the amount of mowing that I do have to do and of course to limit the grass from stealing the nutrients from trees.
My first though is alfalfa and clover but maybe you have better ideas?

How to begin with it? Should I put cardbords for winter first and then start to sow? I don't like the digging approach.

Thanks in advance.

I do not worry about grass robbing nutrients from trees. In the long run I believe they make nutrients available to the trees. comfry can be root transplanted around the base of trees and grass allowed to grow long in pathways then just before it forms seed it can be mowed and used as mulch over the cut and droped comfery.  This makes a soft landing for falling fruit and by snow fall it should be reduced enough to not harbor gnawing rodents although that is not a problem in my area.
I have a plum grove that my syster and her husband planted many years go but after he died it was neglected and then after my syster died I inherited the farm. The grove was not productive because popalar trees had over storied it to the point of starving it for sun and brambels made it inpenatrable. The comfery and rhubarb were still there but the rhubarb had lost its vigor so was not worth harvesting. I began harvesting the populars for firewood and cutting out the brambles. I cut the grass with my power scythe and mulch heavily around the trees. I can easily cut the brambles that cme up through the mulch and the rhubarb is now producing harvestable stalks in the spring. The number of plums that set on the trees has doubled each year for two years. and the plums have been dropping on the hay mulch without damage. The deer now pass through the grove each day and nible back the brambles and prune the lower limbs up to a height that is comfortable to walk under the trees.  I consider it a permaculture success.    
I will try to get back with some pictures tomorrow.

I used Dutch white clover just this year, it is growing low enough that I don't have to mow and when we walk around the orchard the clover just compresses and springs back after a rain. The flowers also attract the bees for fruit tree pollination.
I'm liking this approach for the orchard, and may even try it next year in the vineyard.

I also like Hans' suggestions, our orchard is getting raised beds for vegetables between the trees, with enough space left for harvesting the fruit, the clover that ends up in these raised beds will just get covered with soil and compost, adding to the nutrient level of the beds.
As Hans mentioned, you really don't have to worry about ground covers robbing trees of any nutrients, the value they have as ground cover negates any perceived problems.
If you don't like the idea of planting things, simply laying down a 4"  to 6" deep mulch layer would do fine. Then you can always come along and top dress with compost when you want to or you can plant vegetables or flowers through the mulch.

Redhawk

Finally got back with the pictures.