With proper planting, and a suitable water supply, healthy container grown plants can be planted any time of the year. I've installed anything from annuals, perennials, woody shrubs and trees (all container grown) in the middle of the summer in the deep south. Mulch and moisture are the keys to success.

As a matter of fact, I got a late start in the seeding and rooting of a bunch of my own annuals and perennials this year. They are still growing up in their cell packs, and won't be ready to put out for another couple of weeks. When I plant them, they'll not skip a beat.