Your tuber should be planted when received
Pot size -- The tuber will grow and multiply very quickly and will eventually need a pot at least 14 inches (35 cm) wide, with a height of at least 7 inches (18 cm). But I recommend starting your tuber in a smaller pot, and transplanting it to a bigger pot 3 or 4 months later. As a general guideline, the width of the pot should be twice the length of your tuber.
Soil -- Like most Impatiens, this one likes moist, fertile, well-draining soil. I use a mix of 1 part coir fiber to 1 part perlite (use fine- or medium-grade perlite, not coarse-grade). An alternate mix is 2 parts quality potting soil to 1 part perlite.
Planting -- If you don't see a stem emerging from your tuber, the side which has more root nubs should be planted downward. Plant it with the top about 1 inch (3 cm) under the soil. If you prefer to watch the tuber grow and multiply, plant it with the top of the tuber at the soil surface. Water the soil just enough so it is evenly moist (not fully saturated), and keep it this moist until a shoot appears. It should send up a shoot within 4 to 6 weeks if grown indoors.
Climate -- The preferred temperature range is between 40 and 80 or 85 degrees F (5-29°C). It might be able to tolerate warmer conditions if nights are cool (below 65°F/18°C). If your plant looks unhappy in hot weather, you may need to bring it into an air conditioned, humidified room.
Watering -- Once your tuber sprouts, keep the soil evenly moist. Never let it dry out completely, but also don't keep it constantly soggy either.
Lighting -- This Impatiens does best in bright, filtered light, or morning sun + bright shade. Strong sun might burn or wilt the leaves. In warmer conditions, keep the plant well shaded.
Fertilizing -- Your Impatiens likes average amounts of fertilizer. Feed about every 2 months with a general-purpose fertilizer that contains micronutrients (I use granular fertilizer).
Humidity - Over about 40% humidity is best. Indoors, if your plant seems to suffer in dry air, consider using an ultrasonic room humidifier, which you can buy at home improvement stores and some thrift shops.
Pruning -- Pruning isn't necessary. This Impatiens usually makes a single main stem with few side branches. Pruning the top will encourage the side branches to grow fuller.
Dormancy care -- The plant usually goes dormant in winter, if temperatures are cool enough. If the stem starts to die back or wilt, that's a sign it's preparing for dormancy. This can happen indoors too after a year or two of growth. When this happens, reduce watering.
While the tuber is dormant, ensure that the soil does not dry out completely. If you pull the bulbs up to separate them, place them back into lightly-moist soil, so they don't dry out. The bulbs are fairly rot-proof, but avoid letting the soil get too wet while dormant.
Indoors, the plants may grow continuously for a year or more, until they get tired of flowering and go dormant. Once dormant, move them to a cool spot for 3 months. After 3 months, move them back to a warmer spot to encourage them to come out of dormancy.
Outdoors, the dormant tubers are hardy down the low-20s (-5°C) if planted deep and kept dry and well mulched - but it's best to bring them indoors in those conditions.
Pests to watch for -- Look for other pests that may affect your other plants.
If you have any questions, feel free to contact me.
Good luck with it!
Strange Wonderful Things