Generally, it is pretty easy to tell the weeds from the plants you want to keep. If it pulls out easily & there are only 1 or 2, you didn't want to pull that out. If it is hard to pull up & there are a gajillion around, it is definitely a weed.
Nigella is a bit of an exception, there will probaby be a lot of these, although still easy to pull :) They are very ferny looking & easy to ID.
I think you just learn from experience, I've pulled out many, many that I instantly regretted. I've left many more to grow that I later realized were weeds.
There are a lot of seedling pictures at this site, both of "plants" and weeds,
http://theseedsite.co.uk/seedlings.html

It comes with experience. The nigella looks very much like larkspur. Usually by the time the plant get 2 or 3 leaves you will be able to tell. Most likely you could find a web site that show different seedlings.

I'm afraid there's no trick to it. You'll just learn as you go along. Maybe start with looking up a few of your most common 'weeds' and work from there. The Name that Plant Forum here on GW is a good place to get your mysteries identified.

Thanks - I think that the problem is that I am pulling things (weeds or not) when only the cotyledon is up. Maybe I'll try to wait until there are actual leaves.

I did get excited a few days ago when I spotted what I thought were Hellebore seedlings, there were small clusters of them directly next to a couple of the hellebores, however when I started to see the same thing on the other side of the yard I realized they were un-invited volunteers.

The only thing that I know has reseeded in my yard is a primrose japonica, I have had it for 5 years and it has produced one seedling. Last year I tried saving the seeds and winter sowed them but noting has popped up yet.

Many years ago when I was very busy with a new business my DH helped me by weeding the garden. I later wondered (for a moment) why none of my prolific self-seeders had seedlings. Of course he didn't know a weed from a perennial seedling so pulled everything that was small. He did learn eventually which weeds we have in our garden and only pulled those.

Only this morning I found a mass of seedlings which I wondered about. Decided they are forget-me-nots so transplanted them as a border. Sure hope I'm right and they are not some weed I've forgotten about! :-D

If you take lots of pics of your garden you will know the area the self-seeders were in and will know which potential seedlings might be in each area. Or you could map your garden altho I find pics easier.

flora's advise is spot on. It's how I ID the weeds among the many seeds I put in the yard. Otherwise, you can clear a bed and re-seed each year. This way, you can make sure weeds don't grow among your plants.

In my area i concentrate on dandelions and remove them as soon as I see them.

"If in doubt, let it grow" is my motto. After years of pulling weeds that I am now certain included desired seedlings I have learned to identify most of the seedlings. Those that I am unsure of are left to develop until another gardener identifies it for me or until it blooms. Once it blooms it becomes quite clear if it is something that I want or not. If not, I cut the bloom before it goes to seed and dig the plant out.

Mandolls, I agree, with experience it gets easier. But all of us have the same problem identifying. I find if I mark off an area that I've put seeds in, and then place a plant marker of some kind there, then I am watching for the seedlings. Use the internet to look up the seedlings of the seeds you have sown. Over time, there will be certain weeds that thrive in your area, and you will be able to identify them. If you have cosmos, for example, and you want them to re-seed, then look up cosmos seedlings and be watching for those. Good luck.

I was thinking about this post a little earlier while I was pulling a few weeds...paraphrasing ngraham, if it is tough to pull it is a weed, easy, a flower. So true!
kay

If in doubt, I let it grow until I see a bloom. Then, I usually know if it is friend or foe. I have a lot of fall-sown and self-sown plants. If you can mark a "sample" of each seed in one section, it helps. I've not tried that to great detail--only when I plant something that I think is extra special.

The winter sowing forum also has some great photos (see link) to help ID plants.

Cameron

Here is a link that might be useful: winter sowing forum pics