How to Care for a Potted Plumeria Tree With a Weak Trunk

Place your plumeria in full sunlight. They need at least a half-day's worth of sunlight to bloom and grow well, according to the University of Florida Hendry County Extension.

Fertilize your plumeria every other week from May through September. They are heavy feeders and thrive when given a fertilizer high in phosphorus content. Use 1 lb. fertilizer for every inch of your tree's trunk diameter. Some fertilizers need to be diluted with water, so follow the instructions on the package for dilution. Cover the ground around the trunk, extending to the edge of the tree's canopy. Stop fertilizing in September to allow the plant to prepare for winter.

Water plumerias when the soil is dry to the touch below the surface. They prefer regular, deep soakings over frequent light waterings. Water slowly and stop adding water when it begins to pool on the surface, as they do not do well in standing water. The frequency of watering varies depending on the humidity and weather. Hot periods may require watering your plumeria once a day, while rainy periods may not require any watering. Stop watering in September, when the leaves drop from the tree. Soil that is too wet can lead to the development of fungal and rot diseases, which can also infect the heartwood of the trunk.

Prune your plumeria in late fall, before you move it indoors for the winter. Cut dead or broken branches all the way back to the trunk, but not below the collar (the slightly raised ring around the branch). Reduce the weight pulling on a weak trunk by trimming back branches that droop and by removing heavy branches that compete with the trunk.

Support a weak plumeria by inserting a bamboo pole into the soil next to its trunk and tying the trunk to the pole with rope.

Protect your plumeria from winter frost. They are not tolerant of cold weather and will quickly be killed by freezing temperatures. Move them indoors for the winter if possible.