As I cannot erect the awning on the caravan when I arrive home with it wet, I have fixed awning rail to the fascia board of the garage and use this.Denise
we have a Scenic Plus which we have put up in rain, no problem, apart from me getting wet!
If its wet when we are leaving, we just put it into the shower then get it out on the washing line when we get home when its stopped raining - its dry in no time then back in the bag.
Vegetable matter in the rain? Don't you mean spores in the air?If you need it you put it up.
When it rains you have vegetable matter in the rain, most awning cloths have anti mould treatments. If you "pack" it wet and leave to long or in a warm locker or van the wet combined with the vegetable matter will fester into mould and spores leaving a nice mess.
Just do not leave for more than a day or so if wet. Get it unfolded so the air gets to it and you will be ok.