the heat of the night

peterb · Post by **peterb** » Mon Jun 16, 2008 3:19 pm

Hi- So, the many seedlings that I am tending, which were sown either late November or late February, are all outside for the summer, and have been out for a number of weeks now. They are in trays with window screen for shade, as well as natural shade and filtered light from a couple of trees. A couple of hours of direct sun (very fierce) has so far not seemed to cause any trouble. I'm liking how compact, fiercely spiny and tough the small plants are.

The conditions with which I'm completely unfamiliar have to do with the approaching summer temperatures. I'm not overly concerned about daytime highs from 110F to, occasionally, 120F. In greenhouse cultivation in the high summer in Santa Fe those were highs that regularly occurred. The main mystery for me is how the seedlings will respond to overnight "lows" in the 80s and 90s. In Santa Fe, the greenhouse would go down to the mid-60s, even if the daytime hot spots were 115 or so. These cooler nights largely prevented summer dormancy (except for Pedios, Scleros, etc.)

Last summer, the adult plants exhibited a wide range of responses to the high night temps. I suppose it's highly likely the seedlings will also respond in diverse ways. These are entirely novel seed raising conditions for me. I sowed in fall to try to toughen them up for the brutal summer here, and many of the young plants do seem fairly bulky.

Does anyone have experience getting 4-7 month old seedlings through a summer with high night temps? If we kept the house much cooler, I'd be happy to move the trays inside every night, but we're very conservative with air conditioning, keeping it set at about 83.

My main concern is balancing the extreme dryness and too much water for "sleeping" plants. Suggestions gladly welcomed!

peterb

iann · Post by **iann** » Tue Jun 17, 2008 6:36 pm

80F-90F? Ah yes, that would be the high temperature here, but only inside the greenhouse on a sunny day! My general experience is that seedlings grow regardless for the first year or so. Seedlings have nothing to gain by going dormant, they must grow and either conditions will be good enough or they will die. Warm nights would be stressful because their metabolism is less efficient, roots might not be able to keep up with water loss.

peterb · Post by **peterb** » Tue Jun 17, 2008 9:05 pm

Thanks Ian. I'm hoping they don't go dormant, as it's far easier to water them once or twice a day (yeah, that's what it's been the past couple days) than it is to try to keep them going through a slowdown or shutdown.

peterb

iann · Post by **iann** » Tue Jun 17, 2008 11:04 pm

My little weather gadget says 44C (111F) and 9% humidity right now. That's in Phoenix of course! Its been down to 40F around here this week and we are under a weather watch for heavy rain tomorrow! Shouldn't complain, the garden really needs the water and it has been a fairly sunny spring if a little cold.

peterb · Post by **peterb** » Wed Jun 18, 2008 1:13 am

Funny thing, the national weather service issued an "excessive heat warning." It always seems strange when they do that for the Phoenix area. I mean, 112 is excessively hot, it's true. But it's not like anyone's *surprised* or anything.

peterb

peterb · Post by **peterb** » Fri Jul 04, 2008 4:12 pm

The most heat stressed seedlings so far, with several days already above 110F and nights only down to the high 70s:

Astrophytum capricorne crassispinum
Cochemia all species (halei, maritima, pondii, poselgeri, setispina)
Echinocereus maritimus
Mammillaria peninsularis
cerralboa
multidigitata
taylorianum
brandegeei
aff. boolii
slevinii

All of the above are now inside on a windowsill. It hasn't been a question of water or shade, as I've figured from adjusting these two factors, but plain old heat. I can understand why some of the coastal Cochemias/Mams and E. maritimus were flagging, as it's cool and misty a lot of the summer on that side of Baja. Also, everything except the Astrophytum was sown in Feb., so is only about 4 months old. More established plants would weather the heat better, no doubt (the old C. poselgeri I'm growing doesn't love it, but isn't dying).

Everything else (about 70 species) is growing like crazy. The Neoevansia diguettii had to be moved out of the tray as the stems were pushing against the windowscreen.

peterb

peterb · Post by **peterb** » Fri Jul 04, 2008 4:16 pm

Oh yeah, also, we're experience internet outages and slowdowns to dial up speeds, due to the uninsulated cables from the 1950s that the phone company is still using which the tech/repair guy told me yesterday heat up to nearly 200 degrees and lose efficiency.

peterb

TimN · Post by **TimN** » Tue Jul 08, 2008 6:09 am

For the past 12 days, the low temp has been in the 74-83 range. Highs are in the 104-114 range. My seedlings, planted 6/1, have continued to grow slow and steady.

I'm not sure I could keep seedling this small alive without the plastic bags at these temps.

Tim

peterb · Post by **peterb** » Tue Jul 08, 2008 3:27 pm

It's true that most of the small plants from both November and Feb are basically ignoring the high night temps. Oddly, the growth on the November seedlings has slowed down noticeably, so that the Feb. plants are catching up.

peterb