Last fall I picked up half a large banana plant corm from the refuse pile at the local gardens, planted it in a 12" pot with loamy soil, and stuck it in my growth chamber for months of benign neglect. Now (mid january, -20°C outside) I've noticed suckers coming up around the edge of the corm. Perhaps I watered it too much? The suckers are now 5 to 6 inches (15 cm) tall, and I'm wondering how big a problem I have on my hands. Will these things reach 4 feet in a month? That's too tall for the growth room. Is it time to transplant? Will that slow growth, or should I just clip these early risers, and hope for more shoots come April?
The growth rate depends on the climate. They'll grow super fast in tropical areas, but only a couple feet a year indoors in a temperate area. The problem for you is that they mature rather big. The smaller dwarf edible bananas mature at 5-7', but most will grow 12-25 feet tall or more with leaves up to 9' long and 2' wide.
If you intend to plant them out, that won't be a problem for you. I doubt the shoots wil exceed 4' tall by april, but if they grow too fast, lowering the temperature will slow growth. Clipping the suckers isn't the best for the plant, which doesn't have a great root system yet, and is relying on energy reserves in the corm to produce this growth. You want at least some leaf area, to support the plant.