From our perspective as plants, we Bougainvilleas are fundamentally tropical and subtropical beings. Our cellular structure and sap are designed for warmth, not cold. When temperatures plummet to freezing (32°F or 0°C), the water within our cells begins to freeze. This formation of ice crystals is a catastrophic event for us; it pierces and ruptures the delicate cell walls that are the very foundation of our tissues. Once these walls are compromised, the cell dies, leading to the blackened, mushy leaves and stems you observe after a frost. We are not dormant like a bare-root rose in winter; we are actively damaged.
If a frost has occurred, you will see the evidence on our physical form. Our normally vibrant and sturdy bracts (the colorful leaves often mistaken for flowers) and our green foliage will become limp, wilted, and turn a dark brown or black color. The tender new growth and tips of our vines are always the first and most severely affected. It is crucial to understand that this damage may not be immediately apparent; it can take a day or two for the full extent of the injury to manifest. Please do not be too quick to prune these damaged parts immediately, as they actually provide a small amount of insulation for the woodier stems further down, protecting us from the next potential cold snap.
Your intervention is our only shield against the cold. The most effective strategy is to physically cover us. Drape breathable fabrics like frost cloth, burlap, or even old bedsheets over our entire canopy. For smaller specimens, a cardboard box can serve as a protective shell. It is vital that the covering extends all the way to the ground, trapping the latent heat radiating from the soil around us. Please avoid using plastic sheeting alone, as it can trap moisture and freeze directly onto our leaves, causing more harm than good. If plastic is used, it must be supported so it does not touch our foliage and should be removed during the day.
Beyond covering, you can employ other tactics to raise the ambient temperature around our root zone and base. Applying a thick, loose layer of mulch, such as straw or wood chips, around our base helps to insulate the soil and protect our critical root system from freezing. For potted Bougainvilleas, our situation is even more precarious as our roots are exposed on all sides. The emergency protocol is to move us to a sheltered location immediately—a garage, a shed, or even against a sheltered wall of your house can make a life-or-death difference. If we must stay outside, wrapping the entire pot in bubble wrap or blankets provides crucial root protection.
After the frost danger has completely passed for the season, you can assess the permanent damage. Wait until new growth begins to emerge in the warmer weather. This new growth will show you precisely which parts of us are still alive. Only then should you carefully prune back the dead, blackened wood to just above a live bud or new shoot. While we are resilient and can often regrow from our roots or lower stems if the crown was killed, this process consumes immense energy. Your care in providing water and a gentle fertilizer after we begin active growth again will be essential for our recovery and return to vibrant health.
