It sounds like they have stalled because of lack of water.

They will do better with a thorough (deep) watering every few days until they are bigger. The worst "sin" in Arizona gardening is light watering, because the roots will stay where the water is instead of going deep where they are safe from the heat.

Get a moisture tester and use it. You want the soil to be damp at least 6 inches down so the roots will go there.

Lazygardens:

Thank you. I will immediately go outside and water to a depth of 6". I selectively read the care advice below. Duh? I didn't apply common sense. I missed the clue that plants would become tall and spindly if I were overwatering.

"Yellow cosmos needs only basic care to provide a colorful abundance of blooms all summer long. After the seedlings emerge, water VERY SPARINGLY. In lieu of any rainfall during an entire month, give the planting bed a long, slow drink. Cosmos is drought tolerant, providing abundant blooms with less water than most other annuals. Herein lies the "problem" which many people encounter when growing cosmos -- they "over-care" for their cosmos plants. "Over-care" means too much water, too much fertility and too much shade. When "over-care" occurs, cosmos becomes tall and spindly (even when the new, lower-growing varieties are used), and blooms sparsely. John Thomas says that the best growers of cosmos practice "tough-love" plant culture. "Tough-love" watering means only watering when the cosmos foliage begins to wilt."

Lazy gave perfect advise as usual. I grow cosmos (several kinds) now and then and I water deeply but not very often--they love it. Your penstemon will probably make tons of seedlings if you leave some of the bloom stalks on to get pollinated and make seed pods and then let them dry and crack open to release the seed.

If you don't get any seed pods/seeds, you can buy seed and sprinkle it around mid-summer during monsoon and you'll get seedlings in summer or fall for future blooms. My garden is being taken over (in a good way) with penstemons this year and I love it (P. palmeri, P. eatonii, and a few P. superbus). They're all from a few seed pods from my previous garden and they're going crazy and should be blooming in just a few more days (the eatonii is already in full bloom). I usually trim off most of the bloom stalks as they fade so the plants don't spend too much energy ripening seeds, but I DO leave one or two stalks per plant to get some replacements as my individual plants only last 2-5 years at most.

Keep us posted and good luck with all of your gardening.
Take care,
Grant

Grant,

Thanks for your comments on Cosmos and Penstemon. It's great to benefit from gardening experience of forum members. Appreciate the generosity.