I have planted as late as the end of September, but, personally, I wouldn't plant even that late, if It wasn't "an emergency situation". The plants need, at least in my soil, at least a month of "good growing" before things shut down for winter, and, as you know, Zone 5 is "very unlikely" to get that. I have had pretty good luck with August planted (which seems to be when a lot of vendors ship) but, "June & July" works a lot better...yeah, it's hot and dry, but , a person can always stretch out the hose
. There are also a few vendors who will "spring ship", and that has worked well for me, too.
http://www.cynthiasirisgarden....
I have the best luck, by potting the new arrivals, and only "transplanting them" into the beds after they have made a good root system. Being in pots, it's easy to move them to a "half-day" of shade situation, when it gets *really* hot.
