Answer: There are two plants commonly called red banana. The first is Musa acuminata. The foliage is blue-green, striped with red. It produces yellow flowers with purple bracts, and will sometimes bear small fruit - but it's mainly considered an ornamental and isn't grown for its fruit-production capabilities. The second plant referred to as red banana is Ensete vetricosum. It's a palm-like plant with wine-red coloring on its leaves. It, too, is an ornamental, and will not consistently produce fruit. As this plant grows, it produces what looks like a trunk, with foliage only at the top of the plant.
Ensete is the fastest growing of the two plants. It requires a long, warm growing season and prefers humidity such as it would receive in the tropics. Musa grows into a shrubby clump, usually 6'-8' tall and wide. If you have Musa, they're almost full grown. If you have Ensete, the palm-tree looking banana, its growth might be retarded if it's only 4' tall - it should reach 12'-15' in height at maturity. The problem with slow growth might be with your soil. Soil that's too acidic or too alkaline will bind up nutrients and make them unavailable to plants - even with regular fertilizer applications, the nutrients won't be taken up by plant roots if pH is out of balance. So, if your red banana is Ensete, I'd suggest getting the soil tested and taking measures to correct the pH. Good luck with your plants!
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