I've always thought that the dripline was measured from edge to edge (diameter) versus trunk to edge (radius). Is this not correct? Saw instructions the other day that calculated based on radius and thought I'd research it. There was a curious lack of explanation on almost everything I came across. Lots of diagrams showing the dripline to indicate its outer limits, but nothing to show how the actual linear distance of it was calculated.

For most of the sites researched, the dripline is determined by the widest branch span. This first link gives the formula for critical root zone calculation, and includes a chart showing dripline info. I hope this helps.

http://www.extension.umn.edu/g...

http://treesandshrubs.about.co...

http://www.ehow.com/how_811608...

http://en.wikipedia.org/wiki/T...

thank you. funny how they won't just come out and say it's the radius. but i think i have it straight now ;)

If it gets too easy everyone would do things themselves and the "in the know" folks would be out of a job.. Glad it helped.

At the risk of stating the obvious, most trees are decidedly asymmetrical, not perfect circles, and the drip line will be an irregular area at best. Plus the roots will extend sometimes several feet beyond the drip line so if you're calculating the area for a tree to be watered, take that into account! Also, quirky plants that they are, if they have a long branch extending out one way, chances are they have a long, strong root out in the opposite direction to keep from falling over.

Mother Nature's a pretty awesome engineer, but straight lines, right angles and perfect circles aren't on her list of specs.

so true, thanks!