Answer: Sweet broom (Cytisus x spachianus) is listed for USDA cold hardiness zones 8-10. (USDA zone 8 has average annual minimum temperatures of 10 to 20 degrees F.) Albuquerque is in Zone 7 (average annual minimum temperatures of zero to 10 degrees). It may be that your sweet broom dropped leaves because it was too cold. If the roots weren't damaged, it may come back as temperatures warm up in the spring. As a general guideline, wait to prune any frost-damaged plants until just as new growth starts. Leave any frost-damaged foliage and stems on the plant until then, as they provide protection for the plant from future frosts. You can try scratching stem tissue near the trunk with your fingernail to see if it looks green and living. I'd wait until other plants start leafing out to see if the sweet broom follows suit before declaring it dead, though. Sometimes plants look far gone, but they come back anyway. If you choose plants that are marginal for cold tolerance for your area, it's a good idea to cover them if frost is predicted. Covering doesn't guarantee that they will survive, but it can give them a bit extra protection.
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