I am guessing two reasons. One is the heat wave we are having and the other is that snapdragons are heavy feeders. I always feed them at least every other time I water them. (I just use Miracle Grow 15-30-15) When I did live in zone 8 (I am in zone 9 now and grow them in the late fall for early spring blooming) I still planted my snaps in November as they could easily take down to 25 degrees. Then they bloomed in early spring.
Maybe someone else grows theirs differently or has a different answer.
the likelihood is that it's the heat. the relatively new plant available in nurseries known as "summer snapdragon" is angelonia. thes are beautiful, colorful plants that can take the heat and come in a wide variety of colors. they look too delicate for full sun, but they can take it. half-day sun would be even better.
Thanks you all for the input. I had the seeds and thought I would try them out. It has been in the hundreds here. There also in full sun most of the day. Maybe I'll pull them out and plant some marigolds or Amaranthus there instead.
I can't think of anything worse than marigolds at this time of year. The spider mites will come from adjacent counties to suck the life out of them. Marigolds are spring and fall annuals. The dogs days of summer are already here. Periwinkles might be your best choice right now.
Good luck with your seeds. If you enjoy germinating them, that's the way to go- except, the summer will be over before we know it, and most annuals, including periwinkles, slow down when the weather begins to get cool and the days shorter. I think the shortened days are the main factor. Lots of places are selling plants at good discounts now that Memorial Day is over. The plant sections are virtually empty of customers. If you are willing to buy your plants in 4 inch pots, you'll have weeks advantage over sprouting seed. Just a thought. Growing flowers is for the pleasure we get from it, and if it's more satisfying for you to grow everything from seed, then go for it! Best wishes
My snaps started doing the same thing & I just cut them back & they are re-blooming again like crazy - don't fertilize them & they are in almost full sun. I found that if you can catch them before they stop blooming & cut them back ( I just take the hedge shears & whack the tops off completely ) that you have a good chance of them surviving but if they are already wilting they are gone. Have to go w/dp72's suggestion of summer snaps - I have a full southern exposure & I plant them everywhere out front & they do fine. They do even better if you can plant someplace that gets a little relief from the late afternoon sun. I had 4 I planted around my fountain that got almost 3' tall & about the same around the girth - the cats could hardly find the fountain through the summer snaps & they stayed till 1st frost.Plus they smell like grapes unlike their smaller cousin the regular snap. The perrriwinkles do the same & mine most have dropped some seeds because I have them coming up everywhere this year. Vinca major does the best around here. I rarely have to by more than a couple of small 6 packs of them & they usually end up trying to take over the bed I planted them in - my pinks,corals & purples are almost 8" tall already & not even really blooming yet.Hope that helps & Happy Gardening from N Texas y'all
Catssdawg, thanks for the advice. Mine are still young. Have't bloomed yet. I did intersperse some other seeds with them, but didn't have the heart to pull them out. I put some epsom salts and increased the fertilizer and they are starting to green up.