Growth and overwinter survival of tree–shrub–groundcover plant combinations in above-grade closed, insulated rootzone containers (CIRCs) are being evaluated at Morton Arboretum where winter air temperatures below –11.1 °C (12 °F) are not uncommon. Two-inch-thick extruded polystyrene foam board insulating liner enclosed the rootzone compartment. Triple expanding foam applied where the top insulating board surrounds the above-container plant stems completed the seal preventing heat-moisture transfer and separating the root and shoot environments. Water reservoirs (6-inch depth) in the base of the containers provide additional volume heat capacity. Three plants (tree, shrub, groundcover) were installed in each CIRC. In this preliminary experiment, two 300-gal CIRCs are planted with Picea glauca `Conica' (Dwarf Alberta Spruce), Pinus mugo pumilio (Dwarf Mugo Pine), and Potentilla fruiticosa `Goldfinger'. The two 200-gal CIRCs are planted with Acer ginnala `Mondy' TM (Red Rhapsody Maple), and Hedera helix `Bulgaria' and `Silver Dust'. Control plants are in a field nursery. Within the insulated containers, temperature fluctuations are less extreme than outside. Temperatures within the CIRC have not been below –2.22 °C (28 °F) even when exterior temperatures have hovered at below –11.1 °C (12 °F). Shoot cold hardiness of plants in the closed, insulated containers and of control plants in the field nursery will be compared.