When do the irrigation lines need to be blown out on outdoor green walls?
In northern climates, deactivate the system in fall by blowing out the irrigation lines with compressed air, not to exceed 20 psi, and turning the irrigation controller off. Empty lines and valves are required to avoid freeze thaw damage, so this needs to be done before the first hard freeze of the system.
After blowing the system out, the rain may effectively water the top few rows, and keep it moist until freezing occurs. But, the lower levels can still dry out and should be monitored and kept moist unless frozen.
It is not uncommon to need to irrigate a few times during wintertime warm ups. If needed, you can water with a hose and hand-held sprayer or use the built-in system, then blow it out afterward until the danger of freezing has passed.
If you have perennial plants, throughout winter, the soil should be checked during periods of thawing to ensure proper moisture. The soil should be moist, not wet or boggy, or dry, whenever the soil is not frozen solid.