When ripe, Cleome seed pods explode, throwing the seeds near and far. To get ripe ones, it may be necessary to put some kind of bag over some pods. Old pantyhose work well, if available at your house, whatever can contain the seeds but won't melt if it rains. If you're not expecting rain for a few days, a little paper bag would work fine. Bread twist-tie can hold it on until you see the pod has burst (or hear seeds rattling inside a paper bag.)

Most gathered seeds are a gamble regarding color, if various colors are possible. For trading, it's fine to say they came from a purple-flowered plant but you have no idea if there are other colors of Cleome in nearby yards that could have crossed with yours. Same for zinnia, morning glory, whatever you might have. Nobody can be disappointed or have unreasonable expectations that way. Most who 'must' have a certain color would know this, so hopefully would get seeds from a store/mail company to have a reasonable expectation of precise results or, better yet, get already-blooming plants.

they ripen in order of flowering..

the first to bloom.. will be the first to explode.. and the next day.. the next.. etc ...

just watch them.. and when the oldest opens.. the rest are probably ready to go ...

i quit growing this thing.. because it reseeded itself monstrously ....

the thought that you are going to save seeds ..... and encourage it.. entertains me ...

colors other than the species are bred ..meaning specific moms and dads were used to create such ..... and when you rely on open pollinated seed... eventually they revert back toward the species ... which is along way of saying.. the vast majority will be purple.. but you might get a few otherwise

chime back in.. in a few years.. when you also give up on them.. lol ...

and the fact that they smell like skunk.. didnt hinder my decision .. lol

regardless.. you have fun doing what makes you happy ....

ken

The seeds will eventually revert back to a washed out pink on scrawny plants. What I do is let the purple plants seed, and next year I weed out all but the most robust plants.

You can hold your hand around a ripe pod and it will open and spill seeds into your hand. The darkest seeds are the ripest ones. They need variable cold and warm temps like springtime provides, to germinate.

If conditions are right, one can get quite a few sprouts. Excellent fodder for compost pile when pulled, or excellent as very short-lived mulch if left in place after being pulled. 15 minutes of time would be enough for me to pull these, though I left most of them there to duke it out. I liked them there the year before, so glad they returned the following year, when deadheading prevented a repeat of this scene. Very few things re-seed in light quantites, it's either usually a ton or nothing, if plants are left to their own devices.

I think Cleome smells great, BTW, similar to Lantana and Monarda, fuzzy Plectranthuses.

None of the cleome I started with several years ago has reverted.

Collected some seed to make 'seed bomb' to toss on what will eventually be a widened state highway nearby. It'll be fun seeing them there until paved over.

Rosie, it depends what brand or type of cleome you started with. I've had some come back very weedy and pink, and other seed packets produce purple plants that return purple for years. Good plants?Save seed. Ugly plants? Pullout before they form seeds.