Pruning Shrubs

Question:

I would like information on trimming old shrubs that have been let go too long. They are very overgrown and I'm not sure how to trim them. Also I am wondering how to trim low branches on trees. Can I trim them anywhere so I don't lose all the low branches but can still mow under them or do I have to trim by the trunk of the tree and is there a certain time of the season best to trim?

Minnesota Master Gardeners say:

 If they have been neglected for a long time the shrubs are candidates for a renewal pruning. Remove one third of the old stems in each of the next three years. Prune out the stems from scattered locations on the plant so as to avoid somewhat of a lopsided look when finished. Cut them off as close to the ground line as possible.

Unless there is a major problem with the low hanging branches on the tree it probably isn't necessary to prune. However, if they could result in personal injury when mowing it might be best to limb them up. It's often referred to as 'raising the crown'. Remove the branches at the main stem otherwise branch stubs result which can be an entry point for disease organisms, insects and decay. The best time to prune is in the late dormant season, about the end of March. There is no foliage on the plants and you can see what you're doing. More importantly, (especially important in the case of the tree) pruning at this time of the year minimizes the drying of tissues at the pruning site and allows the early formation of callus, the tissue that seals over the pruning cut. When pruning the tree, take care to avoid flush cuts and do not leave stubs.

The following University of Minnesota fact sheet on Pruning Trees and Shrubs may be helpful: http://www.extension.umn.edu/distribution/horticulture/DG0628.html
The following University of Missouri fact sheet contains some helpful graphics illustrating pruning:
http://muextension.missouri.edu/xplor/agguides/hort/g06870.htm

Purdue University Extension also has an online fact sheet on pruning with some excellent illustrations: It is in PDF format. http://www.agcom.purdue.edu/AgCom/Pubs/pdflinks/HO-4.html

You can search for other University of Minnesota fact sheets on line at http://www.extension.umn.edu/hort/

Your local library also may have a some books on pruning.