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 larger 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 small- or medium-size perlite, not large chunks). 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 sideways about 1 inch (3 cm) under the soil. If you prefer to watch the tuber grow, 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). Keep it this moist until a shoot appears.
Until it sprouts, keep it between about 60-78 degrees F (16-26°C). It should send up a shoot within 4 to 6 weeks if grown indoors, but it may take a longer if it recently went dormant.
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. If you're unsure if the soil is moist enough, try using a moisture meter, sold at garden shops and online.
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.
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). In warmer conditions, mulch the soil, and also shade the pot, perhaps by placing it inside a second pot made of clay. If your plant looks unhappy in hot weather, you may need to bring it into an air conditioned, humidified room.
Fertilizing -- Your Impatiens likes average amounts of fertilizer. Feed about every 2 months with an all-purpose fertilizer that contains micronutrients, following the dosage on the package.
Humidity - Over about 40% humidity is best. If your plant seems to suffer from low humidity indoors, consider using an ultrasonic room humidifier, sold at home improvement stores and some thrift shops.
Transplanting -- Again, the pot should be about twice the length of the tuber. If you're unsure how long the tuber is, feel under the soil. The pot doesn't need to be very tall - the width is more important, since it grows sideways. Avoid breaking apart the soil ball when transplanting, which can damage the roots and lead to wilting. If it happens to wilt, move it out of sun for a few weeks.
Pruning -- Pruning isn't necessary. The tuber tends to make 1 to 3 upright stems, each with few side branches that remain small. If you prefer, you can encourage the side branches to grow fuller by pruning the top of the main stem. This will make the plant bushier. You can prune any time, but do it once per season.
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, keep the soil lightly moist. Ensure that it doesn't dry out completely. Feel free to pull up the bulbs up while they are dormant to separate them. The bulbs are fairly rot-proof, but avoid letting the soil stay 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, perhaps on the floor of a cool room. 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 any pests that may affect your other plants. Try using insecticidal soap spray before using stronger remedies, since some may harm the plant.
If you have any questions, feel free to contact me.
Have fun growing it!
Strange Wonderful Things