Pot size -- I recommend growing your Tree Dahlia in a 1-2 gallon pot the first 2 months, so you can slowly move it from shade to sun during that time. After 2 months, you may transfer it to a larger pot, or into the ground in suitable climates.
Soil -- Tree Dahlia likes fertile soil that is well-draining. An example would be a mix of 2 parts quality potting soil to 1 part perlite or coarse horticultural sand. It is fairly tolerant of a variety of soils, but avoid extremes like hard clay or excessive sand.
After repotting -- The first week, give it bright shade or filtered sun, and no liquid fertilizer. After a week, give it some morning sun or the equivalent, and increase the sun a little each week, watching for wilting or burning.
Planting out -- After 2 months, you can move it to a larger pot, about 3 gallons.
Climate -- Older plants like full sun to a half-day of sun. In hotter climates, some afternoon shade might be appreciated, as well as growing in an oversized pot, to keep the roots cooler.
The young shoots and flower sprays are fairly brittle, so protect them from strong winds, or stake them in windy areas.
Watering -- The first few months, keep the soil evenly moist (but not constantly soggy). As the plant's root system gets larger, you can let the soil dry out halfway, but avoid letting it get completely dry. If the leaves should wilt, water it.
Fertilizing -- Feed about every 2 months during the growing season with an all-purpose fertilizer that contains micronutrients. Stop feeding in September, since it is nearing dormancy.
Pruning -- If you don't want a monster-sized plant, or you want to encourage side branches & bushiness, simply prune the tops occasionally during the growing season.
Flowering -- The plant flowers late in the year, in November or December, so frost may destroy the flowers, depending on where you live. Growing under a tree might provide a few degrees of frost protection.
Dormancy -- Around January, after flowering is done, the plants often drop some or all of their branches. You may cut the remaining branches to the ground after flowering if you wish, or leave them.
The tubers are said to be hardy to 20-25 degrees F (-7 to -4°C) if planted deep and well-mulched. Or just dig the tubers up and move them indoors until about April or May.
Bugs to watch for -- Spider mites, Aphids, leaf-miners, snails/slugs.
Enjoy your plant!
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