I also had cleome in my previous Zone 6 garden. I planted it once and it appeared for many years thereafter without effort on my part.

Based upon both of our experiences in enjoying this self-seeder, I would suggest that you sprinkle the cleome seeds among the emerging poppy foliage in the early spring. According to the seed germination database attached, cleome seed wants light to germinate, so you don't need to cover it with soil. Thus, you don't need to disturb the emerging poppies in order to "plant" the cleome seeds. Let the spring rains wash the cleome seeds into the nooks and cranies of your garden soil and I think Mother Nature will trigger the cleome to sprout when the temperature is "just right".

Here is a link that might be useful: Seed Germination Database

It's my first time to grow cleomes. The method that worked for me well is with the use of peat moss. Here are the steps that I did mid to late May this year.

1. loosened the top 1/2" part of the soil
2. direct sowed cleome seeds about 6" apart
3. pressed the seeds against the soil lightly
4. covered the seeds with 1/4 of peat moss
5. Watered it lightly every 8 or 9am, then 2pm, then around 6pm. I didn't do deep watering. I just made sure they are moistened. I did this step for 10 days then I ignored them after that. I let nature do the rest.

The other method that I tried which only produced like 3 cleome plants is when I sprinkled them over the soil and not covering them. I also watered them similar to how I mentioned it above.

Thank you both so much for your helpful ideas. I really appreciate it. Still thinking about when to do this. Spring sounds like the best time, maybe late April? I did notice a couple stray cleomes coming up in the area and hopefully they will reseed nicely for me to help me out.

Just a thought. When trying to get seed to "naturalize" as you are attempting with the cleome, be sure to sow lots and lots of seed. This is what nature does. Plants make a prodigious lot of seed, but only a small proportion of them come up. Whether you sprinkle and water, or whether you lightly cover and water, use plenty. (like 5 or 10 or more for every one plant you hope to have) Thereafter, Nature should take care of it for you.

Sorry to dig up this post from 5 years ago, but I found this by google. I'm trying to plan a flower bed in front of my deck. I would really love to have poppy in early spring and cleome for summer.

Just want to ask you, is your poppy Papaver poppy or California Poppy?

Cleomes need a cold/warm cycle to germinate, so plant now.