Q. While most of our bougainvillea are in large pots which we bring in doors for the winter; this year we planted one in an above ground planter built around the Jacuzzi. My question is what should I do to help it survive the winter without having to dig it up and transplant it again in the spring. Should that even be an option?
A. I like your idea of wrapping the bases of the plants before any freeze. Unless you have a very warm microclimate in your yard, and there are some in Las Vegas, you will see damage to them at the first light freeze with temperatures below 32° F. Wood mulches will also protect the base of bougainvillea but wrapping it is more effective. This way when it freezes it will kill the top of the bougainvillea to the mulch or wrap and not much further.
Of course this works to temperatures below freezing for short periods of time. If the temperatures are extremely cold or at these temperatures last a long time that it may freeze the plant to the ground. How well you protect the base of the plant will determine how strong it will come back, or not, next spring. Having bougainvillea in the spot in the yard which does not have a lot of wind and is very close to a warm, South or even better yet, West-facing wall will improve its chances for survival.
Plants that freeze to the ground will come back like gangbusters next spring because of their established root system. Plants that are planted in the spring have to grow both the roots and the tops and so growth is divided between the two. Plants that have an established root system only have to grow the top back and so all of that growth goes to top growth and we see huge amounts of growth in the spring.
You do not want to feed them anything this time of year. This goes for any winter tender plant. These plants should get no fertilizer applied to them any time after mid-August. Fertilizers which stimulate new growth will cause the plant to become more succulent and lower its chances of surviving winter freezes. This is not true of plants that have no problem surviving winter freezes. In fact, those plants can receive mid fall applications of fertilizer with no problems. A mid fall application of fertilizer can substitute for a Spring application but not winter tender plants.