If you can keep them in a cool shadier place for now and keep them watered, I don't see why you can't purchase now.
Move into more sun slowly as the temps drop (or that's what I'd do)..since best color will be in sun.

My experience with ornamental varieties is different from dbarron's. I've observed them to be extremely prone to bolting in warm weather. Even deep into fall, should a couple of warmer days come around, the display is ruined.

I usually wait to purchase cabbage, kale (and mums) until daytime temps are in the sixties more or less, and the leaves start falling from the trees, and there's a little nip in the air in the evening that says fall is here. Otherwise it's pretty certain that they'll blow out before the end of the season. I definitely would not buy fall annuals if you are under a heat advisory. If the nurseries are just starting to put them out now, I think you will have plenty of time to purchase them when it's cooler and still find a good selection. Around me (downstate NY), the peak purchasing season, with the best availability, is early to mid October.

Also, if you ask at the nurseries near you, they will probably tell you what you can expect for the season. This was a very common question from customers when I worked at a nursery. We would have a few plants out towards summer's end for those who just couldn't wait, but the large bulk of fall annuals, with the greatest variety, came a few weeks later.

Definitely wait until it cools down. The daytime temperatures should be consistently low, preferably below 70F. Both of these will bolt with hot temperatures, since they are basically a 'dressy' vegetable plant. Cabbage behaves like cabbage & the kale behaves like kale. The very best coloration has little to do with the sun and everything to do with the brisk temperatures. The killing factor will be the first HARD frost, as these can even survive, and even enjoy, light frosts. They grow these in outdoor containers at the malls in Colorado Springs starting in the early fall. THAT should tell you something about what they like. Hope this helps.

Here is a link that might be useful: About growing ornamental cabbage

just remember.. just because you buy it.. doesnt mean its the right time to plant it ...

but waiting to buy.. sometimes mean.. there arent any left when you want them ...

as the barron said... buy now.. place them in the collect place you can find ... the heat itself will not cause the bolting... IMHO ... its the planting.. that interferes with root processes ... that MIGHT cause the bolting... so keeping a pack of them on the north side of the house.. out of sun ... on damp soil .. MIGHT do the trick ...

i presume this is very zone dependent .... such as comparing what peeps in the PNW can do.. as compared to my blistering midwest .... [it was 93 in MI the other day.. i bet PNW hasnt hit that all summer] .. so take everyones advise.. but try to hone in.. on peeps with similar weather to yours ...

ken

Admittedly my experience is slim...I've only bought them maybe half dozen times, but I never had them bolt on me till 2nd year.

I guess if you bought a well bulked up plant, it could have the energy to rush to seed though ?

Just had this crazy thought. The temperature in my garden is the same as the temperature at the nursery nearby. So, what difference does it make if I buy it know or let it sit in the hot air there?

Good thought...and I doubt a nursery would have gotten them too early for your local conditions.

"The temperature in my garden is the same as the temperature at the nursery nearby. So, what difference does it make if I buy it know or let it sit in the hot air there?". albert_135

The difference is, if the plants bolt while at the nursery, they'll discard them and chalk the wholesale cost up to shrink, which is already accounted for in the price customers pay for the plant. Then they'll get fresh stock which has been kept compact using growth regulators (which is why one should not eat ornamental cabbage unless you know how it was grown) or is grown in a cooler climate or was planted later to be freshest during the peak season.

If the plants bolt in the customer's garden, the customer is out the full purchase price and has to buy new ones at retail cost.

Annual plants are often available ahead of season for customers who are willing to risk freezing/flowering out/bolting for the joy of refreshing their garden. The early arrivals are then followed by in-season offerings in greater quantities and varieties.

This post was edited by Cercis141 on Sat, Aug 30, 14 at 19:19