Green roof weeds - The Dirty Dozen

Year after year we battle with dandelions, and a few other volunteer species as well,  on green roofs. It seems that there are repeat offenders, which is admirable in a way and frustrating as well.

So here's a list of the top 12 worst weeds I have encountered in zone 5, 6 and 7 on extensive roofs. There are pictures too, so you can recognize them and take care of them when (not if) you cross paths. The list is just based upon how much I "think" I have seen some of the culprits, the difference may be slight between, say, numbers 6 and 7. But I would bet the ranch numbers 3, 2 and 1 are close to where they should be. One day I'll do a proper count or maybe collaborate with others to generate one.

If you have others to add to the list, think some are higher or lower than they should be, please let me know.

12) Crab grass

11) Blue grass

10) Lamb's quarters

9) Pigweed

8) Purslane

7) Thyme leaved Sandwort

6) Bird's eye pearlwort

5) Mouse eared chickweed

4) Lady's thumb

3) Quackgrass

2) Prostrate knotweed

1) Dandelion

For more on weeds in your area, including how to pronounce them, Penn State has one of the best collections of sources.