Dealing with heat on the patio...

[davelaneward]

Hi. I am not actually growing on a patio per-se, but a tar covered flat roof.

Today, 13th april at 12.20, the temp of said roof is 117f/47c. My young plants are doing well, i have a host of advanced seedlings sitting out there for 5 hours in direct sun, no wilting. But it is going to get HOT out there later in summer. The top soil is at 101f/38c.

1: How do you recommend managing the temps?.

2: I have a cold frame, i am not using it because i am guessing it would get too hot, but maybe the moisture retention would be a good thing?


I plan to get a white textile sheet to lay down under the plants, over a thick fleece type sheet which can absorb alot of water. I will drown the whole thing with water at the beginning of each day to evaporate off throughout the day. which will probably help temps a bit.. Also the white, i hope, rather than black tar, will help lower the ambient temps around the plants too.

Does this sound like it might help?

3: What plants do you recommend that could thrive in such heat? I am trying chillies, tomatoes, cape gooseberry, strawberry and blueberry (there is a bit of shade i could put them in, thankfully).. what other tasty things could i try growing there?


Thanks

[Knight of Albion]

That's a novel way of making productive use of what would otherwise be an unused space.

I had to do a lot of work on my tile roof a couple of years back and yes, without any shade, it can get ferociously hot.

A good watering at the start of the day, yes, they'll certainly be needing that. Probably in the evening too I dare say.

I doubt you'll fully combat water evaporation but some black polythene over the soil base of the plants will help to a certain degree. If you can keep the pots themselves in some shade that will also help.

If you can keep the plants from drying out, then you should be able to grow pretty much anything.

[Nannysally99]

My patio is facing due south and walled three sides, aka the oven. We manage to grow tomatoes, potatoes in bags, strawberrys in pots, sweetcorn will be our latest addition. It takes a lot of maintenance water wise, but sooo rewarding. I cannot say what temp it gets to, I just know the mercury flies out if the thermometer

[PyreneesPlot]

Can you rig up some shading for the really sunny days? Somewhere I saw canes in traffic cones with a netting attached giving dappled shade.
I do that down here for when it gets very hot (mid 30s to low 40s in the shade) just to the young plants.
Excellent use of space:-)

[Two_Sheds]

the temp of said roof is 117f/47c.

Thankfully, it's not (it's not even that hot in the Middle East today). For an accurate reading, you need to place your thermometer in the shade

[Bill HH]

I was wondering if the room below was on fire.

[Potstubsdustbins]

My outside air temperature to day was 15c in the shade but shirt sleeve weather in the sun about 20c, even in the GH it never got above 23c.

47c it nearly hot enough to wash pots.

Potty

[davelaneward]

lol. Thanks for the replies, especially knight.

There is not really going to be much opportunity for shade other than what i can create. I will definitely look to place bags over the soil to keep the water in.

Nanny - thats good to know
Two sheds - i know its not the real temperature, but it is the surface temp of the roof the plants are on. the roof is huge, tarred and walled so it tends to create a genuine microclimate.
Bill - below is a shop, i hope not.
pots - yah, it gets ridiculously hot. good thing is though i laid a white mat out there to check the temp it got to, ive forgotten exactly but it was about 30c/85f while the roof tar was approaching 50c, so i am confident that laying out a well-watered white sheet under the plants will do the trick when its needed.

[Two_Sheds]

Say you've got your oven hob on: the temp on the hob is going to be well hot, burning, but it won't heat up the air around it, nor the whole kitchen.

[Jeanied]

Isn't this all about conducted, convected and radiant heat? Can't remember which is which though

[Potstubsdustbins]

Conducted heat. Heat source needs to be touching article to be heated.

Convected heat. Your radiator heats the room using convection.

Radiant heat. As in the sun warming your body.

Don't forget latent heat the naughty one. Lump of red hot steel turns black as it cools, pick it up it will still take your skin off due to latent heat.

Not much help with this particular question though.

[AllInContainers]

These are my guesses, and they're only guesses ...

Heat absorbed and radiated back will upset brassicas and could cause salad type stuff to bolt. It may however aid germination of certain stuff, and heat loving plants will like it. Radiated and convected heat may increase evaporation from the pots, so you may need to water them more often. Conducted heat will dictate the best footwear when you're constantly going out to water them

If it is tar covered, then at hotter times the tar could be softened and displaced by the weight of the pots ... which will in turn be draining excess water where the tar has been displced when you water them Might be worth putting the pots on pallets or something to distribute the load.

Light coloured surfaces will certainly reduce the heat absorption

... Sorry, I think that's all I've got for you

[Kristen]

I cover my terrace with plants in pots - mostly relatively small pots, the plants are being grown-on. The terrace is sheltered, and benefits from the house behind it; it faces West.

Pots drying out, and trying to water them, and the amount of water "wasted" (running through the pots, or missing them altogether) was an annoyance, as well as the fact that some plants would dry out in less than a day (when they had filled the pot with roots and were overdue to be potted-on into a bigger pot).

Last year I laid capillary matting along the length of the terrace, and then just watered the plants as normal (with a rose on the end of the hose). Same amount of water missed the pots / ran through but was absorbed / held by the capillary matting. Plants grew much better, as presumably they made use of the stored water through the day.

I had a go at fitting leaky-hose along the capillary matting - to save me having to water it at all. I ran the hose up the middle of the matting but the water mostly ran off, rather than into, the matting. There is a bit of a fall on the terrace so that it drains away from the house. If I had thought about it beforehand I would have put the leaky hose at the higher end.

If you fancy trying that capillary matting needs covering with micropore plastic sheet (otherwise it goes green, and roots more easily grow into it, from the bottom of the pots) so basically the micropore sheet prolongs the life of the capillary matting from a season or two to, probably 5 seasons.

I don't know if this will translate well to larger pots, and "crops".

I also have capillary matting on my greenhouse staging. That has a reservoir from which the capillary matting draws up its water. Following this experience by inclination now, if I was doing it again, would be to use "Flood and Drain", rather than capillary matting, so if you can figure a way to rig that up on your roof I think that may be better. Basically trays, which the pots sit in, are filled up with water, left for 10 minutes or so, and then drained. Key advantage of this is that if you grow things that want to be a bit drier, particularly in winter, you can easily accommodate that by reducing the frequency of Flood and Drain. Maybe you would put some sand in the bottom of the trays to have a water reservoir and capillary action equivalent.

[bearded bloke]

What are you trying to protect the plants from,high air temperature or high surface temperature ?
I surface then probably easiest way is to put the plant pots on some sheet insulation material (polystyrene or similar)