Hi! It depends on the shrub that you want to get the cutting from. Flowering shrubs are good rooters in the spring (like now). Shrubs that lose their laeaves in the winter can be propagated in spring. Evergreens & Broad leafed shrubs like Azaleas, Rhodos, and Mt. Laurels are best taken in fall. When taking a cutting cut stems that are softwood (new spring growth) in spring/early summer. Make the cut at a 45 degree angle a little below a leaf shoot down a healthy stem about 6-8 " long or more if you like. Cut all the leaves off the bottom and leave the top ones (like 2 of them ) on the cutting. Most will root best if you use a mixture like Scotts potting soil for seed starting. This can also be used for rooting and the directions are on the back of the bag. I'm sure there's other stuff out there as well. You can then dip the cutting into water and a rooting hormone , like Shultz-Take Root, available at home depot and other garden centers. Pot it up in the soil mix and cover it with a plastic ziplock type bag to hold moisture. Keep it moist and not wet. But, don't let it dry out. Some things take longer than others and some root quickly. Some things are nearly impossible to root! Check out this website if you'd like: http://ourgardengang.tripod.com/CuttingsPlants.htm
They tell me in detail how to do different types of propagation for different things. It is a good reference. Good luck!

Thanks for the help. You gave very clear directions and thank you for the web link. I think I didn't make my question clear. I was trying to ask how you take a cutting from the root of a shrub. Sorry I wasn't clear. And it is evergreen although it flowers this time of year.

I was looking that up on the web the other day. You can search on yahoo and there are several sites that give instructions on how to do it. I think I am going to try it too. Do you think it would work with a Nicotiana? I ordered one online and they said that it had been propagated by root cuttings. So I wonder if that is the only way to propagate that particular Nicotiana? Anyway--Good luck.