First, ask yourself---do I REALLY want to do this Brugmansia do not 'come true' from seeds, for a lot of reasons involving things like the number of gene alleles, recombination, etc. The bottom line is that around 97% of the time, baby Brugmansia’s do not look a thing like their mama, so you have little idea what any given seed will produce. And the dominant color is white, so better than half the time that's what you'll get. Not trying to discourage growing Brugmansia from seeds here; just wanting to save some folks the disappointment. Hybridizing brugs can be fun and rewarding, but it takes a lot of time, room, and patience. Most home gardeners find that they get more pleasing results from cuttings taken from named cultivars, which are genetically identical to the 'mama' plant and grow into plants identical to 'mama'. ONLY plants grown from cuttings of named cultivars can be traded, sold, or even called by that cultivar name. Seedlings, no matter how much they may resemble their mom, are not genetically identical to her. (No matter how much you may look like your mom, or your twin sister, you are a unique individual.) Now, if you still wanna sow some seeds... See the Datura page
Brugmansia are wonderfully easy to take cuttings from. Snip an 8 inch piece off the end of a branch just above a node where a new leaf will sprout (the node remains on the mother-plant). Preferably the cutting should have more than a single leaf on the end of it...if you can find one where the cutting itself branches near the end, that's best. Remove any large leaves from the cutting, but leave a couple of small leaves on the very end. Stick the cutting in a tall glass of water so the bottom 6 inches of stem are submerged. That's about it.
Over the course of the next several weeks you should notice the cutting beginning to grow small white roots. The cutting can remain in the glass (keep refilling it so there's always about 6 inches of water in it) until the roots have grown several inches long and begin curling around in the glass. While the cutting is growing its roots, it can handle at least filtered sunlight (and maybe more).
Once the cutting has a good strong root structure, it can be planted in a medium size pot (at least 8 in diameter and 8 in deep) and given lots of sun. When the roots have filled the pot, transplant into a new container at least 12-15 inches in size. Brugmansia get large fast!
In all but mild winter climates, plants should be brought in for the winter and kept in a cool (50-60°) room. They generally drop all their leaves each winter, so they can be kept where they receive little to no sunlight. Water sparingly during this time.
Warm temperatures, a little fertilizer, bright light, and increased watering bring plants back to life in spring. Prune - hard if necessary - to encourage bushy growth or limit size.
In the spring, wait until all chance of frost has passed before moving plants outdoors. It is preferred to first move them out to a protected area, gradually increasing their exposure to sun and wind over a few days. They grow well in full sun or partial shade and well-drained soil. In full sun and on hot days, they may need to be watered daily. They're generally pretty good at letting you know when they need water. Just watch for the droopting leaves...once watered they'll pick back up within a few hours.
Brugmansias may not flower the first year after planting. After that, blooms open in waves, followed by resting periods. Some people achieve only one wave (probably due to colder climate or shorter summer season) while others get more than one wave. The flowers are beautiful, come in a variety of colors, and smell amazing...especially at night.
Most Brugmansia can grow and flower all year round if they are not exposed to damaging temperatures below freezing. But many Brugmansia enthusiasts live in climate zones with pronounced winters. For these growers it is necessary to cultivate their plants in containers so they are transportable and can be brought into an area protected from frost. The best option for over wintering is in a small greenhouse or other location in which the plants receive full sun. If one maintains the temperature between 54° and 64° F (12° - 18° C), all species and hybrids can be cultivated without difficulty. Most species - in particular B. sanguinea and B. vulcanicola – even flower under these conditions.
Less light is necessary if the plants are stored at lower temperatures. Between 41° and 50° F (5° - 10° C) most Brugmansia growth ceases, so the plants can tolerate storage in darkness for extended periods. B. aurea, B. arborea, B. suaveolens and many hybrids are well-suited to this manner of over wintering. B. sanguinea, B. vulcanicola and B. x flava also survive such a treatment, but will not flower. Although these latter species develop flower buds during the cool winter months, they must have sufficient light to bloom. The heat-loving B. insignis and B. versicolor are unsuitable for cool over wintering under 54° C (12° C).
In the spring and autumn growers must decide when to place Brugmansia out in their summer location, or when to return them again to their winter accommodation. For these moves the following rule of thumb applies: The higher the temperature during winter storage the later the plants should be placed out in spring and the earlier they should be returned to storage in autumn. The most favorable timing for relocation is when the average outdoor temperatures match, as closely as possible, those of the winter location.
In the wild, Brugmansia are found in locations where the soil has been disturbed, such as areas in which vegetation has been uprooted by landslides. Most frequently, however, they appear in regions impacted by human activity, e.g. at the margins of agriculture, along roadsides or at dumps. In such places the soils are often rich in nutrients, especially nitrogen.
Brugmansia are nitrogen-loving plants. Not only do they tolerate high salt concentrations from fertilizers, but they prefer an abundance of nutrients when growing and flowering. In this regard, however, one must consider certain differences among the species and hybrids. B. aurea x B. suaveolens exhibits the strongest growth, often forming leaves to 24 inch (61 cm) length; accordingly they clearly need a higher supply of nutrient than B. vulcanicola, which ranks among at the slowest-growing Brugmansia.
Generally, one can recommend fertilizing Brugmansia in the following manner: A water-soluble, mineral and nitrogen-rich fertilizer (complete with micro nutrients) is particularly suitable. Such a fertilizer should contain approximately 12-20 % nitrogen, 3-6 % phosphorous and 8-12 % potassium.
During the summer main growth period the plants should be fertilized twice a week.
These relatively high nutrient applications should be reduced however, if
Fertilizer rates must be adjusted for the time of year, particularly for container plant culture. Before winter dormancy, in which the plants are to grow as little as possible, fertilizer amounts should be gradually reduced. During the winter Brugmansia should be fertilized sparingly. The dose is then raised slowly again at the beginning of spring.
Brugmansia that do not receive sufficient fertilizer exhibit slow growth, have light green leaves and produce few blooms. That the leaves have become a light green color becomes particularly evident after administration of a liquid fertilizer. After no more than three days from fertilization, the youngest leaves at the branch points become noticeably darker than the older leaves. On the basis of such changes in leaf color one can estimate the approximate nutritional condition of the plant. If the color difference remains very evident after several fertilizations, one should adopt shorter fertilization intervals. If a grower is uncertain about the success of a fertilization regime, or requires an exact nutrient profile, a plant sample or leaf should be submitted to an appropriate service or laboratory for analysis.