It was 93F in San Francisco, but I had no damage to anything except a tree fern. My membranacea did fine in the full sun, probably because I kept it misted several times a day. My antioquiensis got a bit droopy even in full shade, but it quickly perked up again when it cooled. I'm glad the heat is over for now.

Just a follow-up (I'm still curious if anyone else has anything to report--thanks Dave)

Here are temps over the last few days, and lowest relative humidity at what I think is a reliable local weather station:.

date, hi/low (F), lowest relative humidity

16th 64/38 36%
17th 74/39 28%
18th 81/48 28%
19th 91/49 23%
20th 95/55 14%
21th 94/57 18%
22th 84/56 32%
23th 69/52 34%
24th 60/46 34%
25th 64/44 41%

Our average high/low is about 70/50 this time of the year.

A couple obvious things: the day/night difference was enormous when it was hot (42 degrees on the 19th). Humidity was very low when it was hot. The first should work in our favor, the second against us.

Here ae the cool growers and how they fared:

All had rapid growth during the hottest period: >1 inch/day for those measured; P. tripartita var. mollissima, P. x exoniensis x parritae and P. membranacea.

For each plant: sun, damage, other comments

P. x exoniensis (2 plants): morning sun, no damage. No bud damage apparent (yet). One plant's soil dried and plant wilted yet recovered completely, other has 3 open flowers today. In 1 gallon pots.

P. tripartita var. mollissima. Filtered A.M. sun with lots of afternoon sun. One growth point died, essentially one leaf per vine was damaged. Plant is in the ground.

P. x exoniensis x parritae. A.M. sun. No obvious damage, 5 gallon pot.

P. manicata. A.M. sun. No obvious damage. 1 gallon pot.

P. membranacea. Was: P.M. sun, Now: mostly shade. 1 growing point died, at the same time new ones popped up elsewhere and grew very rapidly. Sunburn on a couple leaves where sun exposure was unchanged. 7 gallon pot.

I decided to list all this info since this was a particularly early and sudden shift in temperature--the plants were not adapted to heat. There are more or less predictions of doom out there for these plants when temperatures hit above 85 F and certainly above 90 F. All growth will stop, buds will drop,etc. For this limited sample, little happened and it seemed restricted to plants in the sun. It can get hotter than 95 here, though.

The only cool growers wih buds or flowers were the P. x exonienesis.

Perhaps heat with sun is a greater short term danger than heat with low humidity in the shade.

The fact that growth accelerated conflicts with what I've generally read; however our average temperature was not really that hot.

Regarding Dave's comments: I also had slight damage to a tree fern. A P. 'Lavender Lady' in a pot aborted a few buds. No doubt there was other damage. Temperatures this hot and this early are pretty much unprecedented.

For the record, it got up to 92F in my part of the SF South Bay area, a little closer to the bay than the original poster.

I'm growing P. pinnatistipula and P. membranacea, both fairly small plants in 10" terracotta long toms. They get mid-day sun, but the pots are shaded, and they were well-watered during the heat wave.

Neither plant showed any damage, or even afternoon wilting, whatsoever. Both plants grew vigorously on the hot days.

I thought I should mention that I had recently bought the P. membranacea, so the sunburn could have been due as much to a move to a new, sunnier location as to the heat wave per se. It was probably a little of both. The plant overall, though, is beginning a very strong growth phase. I posted a picture of it just over 3 weeks ago. It has since sent out at least 6 completely new growths, now in the one to six inch range, with more to come. It will soon be a much larger plant than when I bought it.

The P. tripartita var. mollissima was in the ground and was kept moist, so the damage to new leaves was presumably caused by the heat and/or dryness of the air.

P. x exoniensis continues to form very young buds. Production of buds has not diminished, and buds at all stages of development seem to have been unaffected.

The plants continue to grow fast, but not as fast as during the heat. It's been mostly in the 60s with lows in the upper 30s to 40s since the heat ended. I suspect some weather around 80-85 with cool nights would stimulate a lot of growth.

I just wanted to resurrect this thread since we've now had our FOURTH heat wave of the year. I also want to get Eric's observations since he's considerably warmer than we are.

As far as I can tell there haven't really been significant effects on my "cool growers". P. x exoniensis took a break in flowering in June for a week or two, but this may have been due to transplanting a month or two before--I'm not sure. Today it was 99, yesterday I think it was a degree or two cooler, and my exoniensis is going strong. Today it had 3 flowers open.

In the week after our previous heat wave I noticed my P. exoniensis x parritae had formed its first buds. These are on the small side, so it's possible they are in the process of aborting--I'll have to wait to find out.

My P. tripartita var. mollissima still hasn't bloomed, although it's definitely blooming size. I assume this might be due to the heat, and I look forward to seeing it bloom in the Fall.

Overall, though, I'm not aware of the heat causing any problems.