I've had to think on this a bit. Most seed packs claim that temps should be kept optimally at 75 degees F. Here in BKF, CA, air temps have been in the 90s and are amplified by a concrete patio deck. Results of that elevated temperature are 2 fold, 1) the top inch or so of soil drys out quickly, almost daily and 2) the dark soil actually raises the soil temp above the air temp due to absorbtion of solar energy. Further, where I've found a withered seedling, I've emptied out the container to be surprised to find that even with ample watering, the interior soil had gotten dry as dust.

So there might be 2 solutions if you are trying to sow seeds in a hot dry area like the American Southwest, 1) Use Vermiculite on the surface to seal in moisture and make better use of shade and the lower temperatures in the shade zones. Note also that vermiculite is light in color and reflects sunlight, helping to reduce soil temperatures. I don't know if that might have the effect of raising temps immediately above the soil surface though. Clearly, screening material was not enough to cut back solar temps here. Raw shade was required. Unfortunately, some seeds require the stimulus sunlight to germinate.

I suppose the most elaborate solution would be constant or intermittant misting with cold water. But for sure, there's an argument here to invest in hydroponics and artificial lighting.

Getting that optimal 75 degree F temp is a tough one here in Bakersfield which is said to be the 2nd driest city in the continental US, behind Las Vegas.

Cannas have now sprouted and are doing fine now, putting on multiple leaf growth and about and inch and a half high and healthy green. Other seeds continue to resist germination including, Gingko Biloba, Tebebuia Chrysostricha, Rhodendron, Senecio, Tasmanian Tree Fern, Aloe and others.

It seems that even with plenty of water, you can't germinate seeds in a desert unless you do it indoors sharing Air Conditioning with your seeds. After getting them started, they seem to do OK in partial shade.

Live and learn ...

Thank you,
This might explain why my seeds aren't germinating in my cold frame outside where the temperature exceeds 100 most afternoons.
My garage is about 70 - 80 degrees . I'll try that.

Thanks,

Mike

No Problem Mike.

I think I've actually seen some seeds cook here. Some of my Cassia Alata sprouted, but others under plastic covers are soft and pulpy and well ... I think they got cooked. However, I've got about 10 Cassia Alata sprouts that are about three inches high now, so no loss. The leaves brown on the edges in this heat, but they are growing.

My Canna are doing fine under screening in the middle of the patio ... now that they have sprouted.

I have an AeroGarden which I bought to try hydroponic seed starting. Threw away the Gourmet Herb Seeds and substituted my own choices. The AeroGarden has its own source of lighting and can be kept indoors out of direct sunlight and the high temps. Hope to have better luck with the tougher seeds I am trying to germ. It's just about too late to try and germ them, but I'm trying some Lantana seed. They are described as slow to germinate, so this should be an interesting test.

Here ya go, photos of my Canna seedlings ...

A number of seedlings growing in my soda bottle planters:

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Close-Up of the first to sprout:

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Beautiful, aren't they?

Moving seedlings into the cooler temps of shade has just given me another germination success. My Aloe Thraskii are sprouting now too!

Yeah!!!!

Thanks - I loved the pictures! My 5 are doing well, and are fun to watch grow.