I don’t have any personal experience with this, but I imagine this would get awfully hot. All the nurseries and even the big box stores seem to have the pots on wooden pallets if they are out in front on the asphalt around here.

black pots.. on black top ... in blinding sun.. is a pot media heat issue... which is ultimately a watering issue ...

which is most likely controlled by the type of media... how it drains/retains water.. and how often you can water them ... is there a water source ???

in such cases .. i have seemed to notice that often ... pots are grouped close together ... so that only those on the edges are in bad shape ... the interior pots actually being shaded by the outer ...

also keep in mind... asphalt or black top retain heat late into the night ... meaning there might not be the cooler night recovery period ...

ken

I think the asphalt is less of an issue than the absolute certainty that pots will get knocked/kicked/blown over, losing potting medium and even plants. I have no real problems in keeping a huge number of pots directly on top of hard standing (nothing like as many as thousands though) but make every effort to maintain some sort of barrier system using gravel boards to knock together narrow 3foot wide frames, where square pots can neatly abut each other and make the most of available space.

What sort of summer temperatures do you see over there in the UK, Campanula? The OP should see summer highs in the upper 80s on average, and if your temperatures are significantly different (some places in the UK see summer highs in the 70s???) then your experience with pots on asphalt may not be that similar.

I used to work at a retail nursery, and during the peak season, we had an overflow of plants sitting on asphalt. Had to water them twice a day to keep them from wilting, and still would lose some. Of course that is in the southern United States. We get HOT during the planting season.

I'll definitely have a daily watering routine and will plan on using a shade cloth to tone down the sun's intensity. Like most of you, I also group plants as close as I can to regulate pot temperature swings.

I had a grower mention I should paint the ground green or red too? Anybody ever heard of doing this or what the point would be. I haven't had a chance to further discuss reasons with her yet.

Glad you mentioned the chances of containers blowing. I didn't even think of this so I'll need to watch carefully and address it as needed.

Any thoughts on possible drainage issues with plants sitting on a non-porous flat surface? The standard containers have drain holes in the pot corners so I think it would be fine but the lower openings would have a tougher time draining.

When I had my nursery I grew, sold and overwintered all my plants in ground beds. Iy will depend on your winters if you'll need to cover,

https://wordpress.com/post/theherbladyblog.wordpress.com/453

Once ganged up he plants still be surrounded by open asphalt? That radiant heat warming and drying out those plants all night is what I would think will be the issue. Even on concrete after a hot summer day, you can go out at night and feel the heat coming back from a driveway Or brick home.

Can shade cloth would be great.

Could you rig up a cheap nursery table setup with free pallets to get the plants off the asphalt and shade it a bit?

Painting that asphalt a lighter color would reduce the heat gain all day ... that sounds light a good idea too.

One of the concerns i think, is the heat rising off the asphalt. Changing the color from black to something else can help. Another idea provided was to put them on pallets. Considering that pallets are often available for free, this could be a feasible option. Or else, use the pallet wood to make other kind of shelving system, if you need to.