When I worked in a commercial greenhouse we would sometimes get some in a flat of seedlings. We could not weed them out as they would scatter seed at the first touch. We would carefully lift the flat and take it out side where we could weed it without getting the seeds in other flats. I know of no miracle solution other than patience. Al

That must be it, when I rub them out I only make the seed all the more.

There may still be seeds in the soil from the previous year. Unlike our vegetable seeds, many weed seeds can remain dormant in the soil for years and continue to drive us crazy. Be sure to get rid of the stems, because they can grow into new plants. Covering it with peat moss will probably not work. If you're not growing anything in the area at the present time, you can solarize the soil.

Or you could try a flame weeder.

Carla in Sac

Watch out with those propane weeders. Mikey set the roses afire.
Renee

I was going to try covering all the soil with peat moss, if compost makes it worse, but I never got around to going to OSH today. It is a soil area under a tree on the northern shady side in which they are the worst. Peat does make the soil softer, but I have not used it in years. If it was softer, it would easier to turn, but maybe I should consider round up? They are very small plants and I think even after round up they are still making seeds. Round up takes two weeks to kill the plant. The tiny little plants have the tiny white flowers on them. You can barely see them at all, and they already have flowers.

I am not even sure it is Hairy Bittercress. It could be Wavy Bittercress. Some are small with tiny white flowers, but some have brackets that look like antennas, that seem to launch the seeds in the air. I found one of the antenna ones under a fern yesterday. Unnoticed it has been launching seeds for a long time. Maybe they are two different plants?

Cardamine. Mine looks like "Hairy Bittercress" in web photos, and like those, mine is completely unhairy, nonbristly, smooth. Every part. Some ambitious lawyer needs to sue these weeds for false advertising. :-)
Wavy Bittercress in web photos have leaves with irregular edges.

"Some are small with tiny white flowers, but some have brackets that look like antennas, that seem to launch the seeds in the air"
The seed capsules are held high and almost vertical. Yeah, seeds "pop", i think about 2 feet.

"Unnoticed it has been launching seeds for a long time. "
You're in SF, and your Cardamine are already launching seeds. Are they in sunny dry drained environment, maybe? Aren't Cardamine only cool season annuals in SF?
2 warm days, and my earliest ripeners will launch (except I expect to prevent that).

Every weed (and non-weed!) has weaknesses.
i think unsprouted Cardamine seeds don't live many years. The plants pull easily instead of breaking above the crown. (Poa annua also pulls easily for me) Chips or thick layer of tree leaves stop them from sprouting. 1.5 foot or taller dense plants should smother them.
I am wiping out some (using mostly roundup, since in an unplanted area) that i hadn't hammered consistently in past years (they should be gone in 3 or 4 years). Cats or dogs have *started* cardamine far away, but those disappeared in a few years of consistent pulling. I think my first patch arrived in tire tread.

The usual source is Weedy Potting Mix. (accept no substitutes! and don't accept the genuine weedy mix either!)
I avoid acquiring plants in pots. I prefer seeds. You can shake most of weedy mix off roots, into your trash pickup can. Replant plant immediately into good potting mix. (then accidentally forget to water it, as usual! ÃÂ ÃÂ ÃÂ :-( ÃÂ ÃÂ ÃÂ ÃÂ )

Retail nurseries, and weeds:
Yardbirds had cleanest that i recall. OSH has been worst. I've seen weeds in some homedepot pots. I haven't been to lowes enough to notice. The nursery-only nurseries seem good, but one i visited years ago had weeds in their sick plants (or that's what i think the collection was)

I removed every little weed and then I check under all the plants for those hidden ones and I found a few. I think once I get rid of those hidden ones, it will improve.

I used to have more poke weeds then anything else. They came from the neighbors when the fence fell down. His water line burst and all this water came from his yard into mine. It brought all these poke weed seeds. It took years, but now I hardly ever see any poke weeds.

This weed is pretty annoying, but at least it disappears when the weather gets warm down here... Anyone know the ideal time to apply preemergent for this beasty ? I would think early winter...

Preen won't work for me, because my soil has too much OM. I once put in under a bench I had and it killed the near by lawn. I would only use preen in an area far away from any thing I was planting.

Bittercrest grows in summer and winter here, because we don't have a hot summer or a cold winter. It does like a lot of water and shade. It least that is where it is growing right now. Preen it does not kill the seeds, and once it wears off they will sprout again. So, you have to use it forever or just give up using it. Preen only keeps seeds from germinating, and is more harmful then round up.

Preen says you can use it any time, but you need to apply it every four months. So, that is summer winter fall spring, unless you have snow.

We have been fighting bittercrest for years and have finally made some headway. We are in zone 5 where it germinates in the late summer / early fall and appears as a green mat until February. It starts blooming long before it is warm enough to be outside gardening and is going to seed by the time we are beginning for the spring. Last year I sprayed it with round up throughout the fall into early winter and got out again early in the spring as soon as the snow was gone. It really seemed to make a difference. Far less plants, hence seeds. I understand that one plant can throw seeds as far as 20 feet. Anything that was coming up in the lawn around the flower beds, I mowed the flowers off with an old fashioned, human-powered lawn mower. This was our best year ever. I am planning on adding a pre-emergent to the regiment to prevent fall plant development. I am determined to win this battle without a flame thrower, although I would really like one.

I got rid of it. I had to go under all my plants and find the hidden plants that were making seeds and throwing them up, but I finally got them all. I have not seen any of it in a while now. But, I have baby tears and some purple colored oxalis, that are plaguing me, and some other thing I think it's pig weed.