I have a cultivated native wildflower patch. I do not recognize this clump of seedlings that is growing in the area and am wondering if it’s a weed? I can recognize most weeds in my yard but this one I have never seen. Also, can you provide advice on when to cut back old dried flower stalks. And to what height should they be cut back?
Multnomah County Oregon
The plants in your native wildflower patch look like bittercress (Cardamine hursuta). It is one of several weeds from the mustard family that grow very well in our early spring, having germinated last fall, slept over the winter, and with warmer moist temperatures is ready to go. The plant is very happy in the moist cool conditions of our early springs. It's edible. The leaves are quite tasty. Try it on an open-faced sandwich. This article gives additional information, Weed of the Month: Hairy Bittercress https://www.bbg.org/news/weed_of_the_month_hairy_bittercress
Bittercress isn't a bad weed, and as the weather warms and dries out, it isn't much of a problem. However, unfortunately, bittercress reseeds itself enthusiastically. When mature, the seedpods explode scattering seeds 3 feet away. Fortunately, because of its shallow fibrous roots, it's easy to pull.
There are several mustard family weeds that appear during our springs. They all develop from rosettes and all have 4-petaled flowers. Some are small and have small star-like flowers. It's nice to see them after a gray wet winter.
After a more careful look at your photo, especially the seed pods silhouetted against the turquoise, the weed is not bittercress. It is most probably shepherd's purse. Bittercress seed pods are long and narrow. The seed pods from your weeds are not yet fully formed, but look like the tiny purse-like structures of shepherds purse seed pods. As the seed pods mature they're easier to see. This article has additional information and illustration of the features of this plant, Shepherds Purse http://www.weedinfo.ca/en/weed-index/view/id/CAPBP. You can also bring a few of the plants to your Multnomah County Master Gardener Office (2701 NW Vaughn Street, Suite 450 [4th floor Montgomery Building]; Portland OR 97210;email@example.com; 503-445-4608; open M-F 10am-2pm). The Master Gardeners have excellent expertise identifying plants, and can look at the plants under magnification. Since one of the distinguishing features is hairs on the leaves, they can show them to you. Unfortunately, shepherds purse can live and produce seeds from now through to fall if conditions are right. Removing the plants before they shed their seeds is important. Like bittercress, shepherdspurse mature seed pods split and eject their seeds around them.
Shepherds purse seedlings are tiny, so organic mulch is very effective at blocking the light the seedlings need to develop. Covering your wildflower patch with mulch in the fall should help control their numbers next spring. Mulch will also be good for your wildflowers.
Leave the old dried flower stalks for the birds, and cut them back at the base when the plant starts growing vigorously.