Sunday, March 10, 2013

Ragweed or Cosmos?




A row of ragweed sprouts next to one Cosmos seedling.

Cosmos seedling has a few lateral rootlets off the primary root.

Ragweed has long shallow root with rhizomes.

Ragweed on the left, Cosmos on the right.  Don't confuse the two!

Last summer I let a young plant grow in my flowerbed.   It looked to me like a Cosmos (C. sulphureus) seedling.   When I noticed it again, it was not a beautiful, glowing Cosmos, but a mature ragweed.  I pulled it up, of course, but too late.  This February, I had hundreds of little ragweed babies popping up in that flowerbed.  Arrgh!

To be sure I would never make the same mistake, I took these photos of a cosmos seeding next to the ragweed sprouts.  I might still confuse the foliage, but there is NO WAY that I will mistake what happens under the soil with the roots!  The Cosmos seedling has only a small set of lateral rootlets of the primary root.   The ragweed has a clever, extensive underground system of threadlike roots and rhizomes that supports multiple plants.   To get it under control, I dig up each bit of ragweed and collect as much of the root system as possible.  I declare that this flowerbed will eventually be ragweed free.

2 comments:

Cristy said...

Thanks for posting this. This is my first year to grow cosmos, so I was wondering how to tell it from weeds. Now I know.

Sally said...

Hello Cristy! I am glad to hear that this was useful. I figured I could not be the only one who had trouble telling these guys apart. We love cosmos - so many butterflies and bees use it for nectar. You'll be able to save seeds for next year, too.