The ones pictured are just starting to flower. That means there is the entire flowering and seed maturation phases to go through before you can collect seed. I've never timed it but I would say that it would be in excess of a month before the seed could be collected.

FataMorgana

Thanks for the info. It's been a month since my post and the seed heads look like they are finally drying out. I was planning on tying little baggies around a few to collect the seeds and cutting down the rest of the plant. Then hanging the seeds up in a brown lunch bag to finish drying. Is that a reasonable way to do this? I've never saved seed before!!

Thanks!

I try to let seed dry/mature as much as possible on the the plant to improve seed viability. You don't want to collect before they've finished maturing.

If the flower stalk is turning yellow/starting to dry up, the plant is done giving the seeds whatever it can and you can collect with no worries.

FataMorgana

If you plant parsley 2 years in a row & let them go to seed the 2nd year you'll have parsley planting itself for you. Then you won't have to collect the seed, sow it, water, etc. It's finally worked for me.

I was too tidy in spring with the parsley snipping off and then mulching around the other plants nearby, so last summer I made sure I didn't clean up too much nor mulch over the seeds. I let several plants go to seed & do their own thing.

This spring I have 100s of parsley seedlings in 2 different raised beds. I've had enough to move around & pot up to give away to garden friends & at swaps. Some of the early summer sown plants are going to seed now, so I'll let them set seed again. That way I'll have plants next spring, too. Once you know what those seedlings look like you won't pull them as weeds.

Thanks for all the tips! I'm keeping my fingers crossed!