Container size -- Use a pot about twice as wide as the one it arrives in. Plan on transferring to larger container (or into the ground) when the roots poke out of the bottom of the container - probably in a few months.
For soil, use a well draining mix. Personally i use a mix of 1 part coco fiber to 1 part perlite (use fine- or medium-grade perlite, not coarse-grade). An alternate mix is 2 parts potting soil to 1 part perlite.
Transplant tips -- Before removing your plant from its pot, give it a watering if the soil looks dry, so the soil doesn't break apart, which can damage the roots.
Light -- Your plant was grown in filtered light, not direct sun, so it should be acclimated to direct sun slowly. This will give your plant time to grow a larger root system, so it can handle more light. So start your plant with either tree-filtered sunlight, or morning sun, so that it gets about 25% sun each day. Every few days, move the pot into slightly more sun. If the leaves should wilt, simply give it a little more more shade for a few days. Eventually work up to about 75% sun. They appreciate some afternoon shade in warm areas.
Watering -- Iochromas do best with regular waterings. Don't let it dry out completely, but don't keep it constantly soggy either. You may use a moisture meter to monitor the moisture levels down in the root zone.
Fertilizing -- Feed your plant about every 2 months during periods of active growth using a granular fertilizer that contains micronutrients (I use this). Follow the dosage on the package.
Placement in the garden -- Full sun may be too much for this Iochroma, except in cool areas like near the Pacific coast. It might need some afternoon shade in hotter conditions.
Protect it from frost the first 2 years. Mature plants can tolerate light frosts, but may lose branches.
Over about 40% humidity is best. If your plants seem to suffer from low humidity indoors, consider using an ultrasonic humidifier.
Pruning & shaping -- Pruning isn't necessary, although you may prune it to shape it. Prune in the fall to avoid removing budding sites, unless you grow it indoors, where it can flower throughout the year.
Bugs to watch for -- Spider mites (tiny "dots" under the leaves), mealybugs, aphids. Try using insecticidal soap before using stronger remedies, since some may harm the plant.
If you have any questions, feel free to contact me.
Enjoy your plant!
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