Heat tolerance of plants

[PeterS]

I have just had a freestanding garden room built and plan to grow a permanent display of some tropical plants. I have been keeping the doors and windows closed, as much as possible, to keep the temperature up as the plants seem to be doing well in the heat. Canna altensteinii has already reached 7 feet, from a rhizome. The humidity is also high, almost 100% at night and falling to 75 or 80% during the day.

But how high can temperatures go. I understand that plants start to sustain cellular damage at 30C - but many places in the world must be hotter than that. I am currently planning summer daytime temperatures of 25C to 30C (when the sun allows).

It obviously depends on the types of plant - currently Canna, gingers, bananas, Alocasia and Calocasia, various climbers - Thunbergia, Pandorea, Clytostoma, Ipomea, and Justicia, Pachystachys, Tibouchina etc and a few Palms. I obviously need to chose a climate then select suitable plants. Any thoughts?

Is there a good source of AHS heat zone information - its rarely quoted, and does it mean anything. The only source that quotes a figure for Tropaelum speciosum says zone 1 to 12. Well 12 means it will tolerate 210 days over 30C - I am not sure that that is true.

[AndyC]

Most of the plants you have mentioned will love the high temperatures and humidity although Tibouchina doesn't like extremes of temperature (hot or cold). The hot house at the Ventnor botanical gardens on the IOW has no discernible ventilation and when we went last summer was nearly 100% humidity and about 35C which the aroids, gingers and cannas were loving but I wilted very quickly.
What are your minimum winter temperatures going to be?, that is probably more important than the high temperatures if you want a permanent display. how about a few pictures of your new tropical house please?

[PeterS]

Thanks for your reply Andy. Interesting about Ventnor botanical gardens. My current thought is to have a minimum winter temperature of 10C. I understand this is enough to allow many plants such as Canna and bananas to continue growing rather than going dormant. Its not set in stone - it could change, but it would obviously be more expensive to have a higher temperature.

I wondered about Tibouchina (and Pandorea). As Australian plants I assumed that they might cope with the heat, but might not like the humidity.

I will put some pictures up in a short while. The garden room floor was tiled today - so everything is a bit disorganised, with all the plants outside.

[PeterS]

This is the garden room, just after it had been built. Because its freestanding by the garden boundary, it was limited to 2.5m (8ft) in height. So it had to be a reverse lean-to design, that the builder (and none of the others that I approached) had ever done before. I am very pleased with it.


It has just been tiled, and I have fitted vine eyes and wires along the back wall and across the roof. I started putting some plants back inside today, with 9 climbers across the back wall.


The intention is to make it into an indoor jungle garden, rather than just treat it like a greenhouse doing everything. But I have no idea how I want to eventually lay it out.

[charlie]

Its lovely - clearly not big enough , but lovely :)

[PeterS]

Thanks Charlie. Your Ipomea indica is already starting to go across the roof. And yes, you are right about not big enough. :)

[AndyC]

Its lovely - clearly not big enough , but lovely :)

It needs a good bit more headroom ;)
but I'm extremely envious. It looks a lot more classy than my polytunnel.

[Chrisg]

Very nice. Were you tempted to leave some open ground to plant into? Have you seen Melissa's cactus house, not sure if there are any picture on here.

[PeterS]

No, the question of open ground didn't really arise. It was replacing an old, smaller, summerhouse where I overwintered plants. As everything was in pots there, I decided to continue to use pots. And no, I haven't seen Melissa's cactus house.

I have already noticed my first casulty to the heat - Asclepias curassavica. It doesn't really need to be inside, but I understand that it likes heat but not over 35C. Part started to wilt when the temperature reached 33C, so I brought the temperature down with ventilation. Curiously the wilted part has never recovered - I can't see any physical damage - so I assume it was the heat.

I am tempted to aim for a temperature of between 25C and 30C, and grow plants that are suited to that. But I would like to find a list of plants that enjoy those conditions.

I found this quote in relation to the Amazon rainforest.

Like any other tropical rainforest, it's hot and humid throughout the year, with an average annual temperature of 27°C (80.7°F). There isn't such a thing as summer or winter, or it's not pronounced, the annual temperature range is about 2°C.

which is less than I would have thought - though the humidity will be high.

[Phemie]

Fantastic. You will have lots of enjoyment from it although the plants will soon be competing for space.