"Jimson weed." A green-stemmed, hairless annual, 2 to 4 feet tall, with few branches and two 8 inch long ovate leaves. The flowers are white, 4 inches long. The capsule is egg-shaped, to 2 inches long, filled with many black seeds. In D. Stramonium var. tatula the flower is violet-purple or lavender; the stems are purple. Naturalized throughout the world. They are easily grown from seeds, which sprout quickly even without bottom heat. Does well in rich soil in a dry, sunny location. May be sown in the open in May in mounds 18 inches apart with four seeds in each mound. Thin out all but the healthiest plant after sprouting.
Cultivation and Propagation:
The herbaceous daturas are generally grown from seeds in early spring. They should be started in flats indoors in
the North, or where they are to stand in warmer areas. The perennial kinds usually rise from thick tuberous roots.
In the North these may be dug in autumn and stored in semi-dry peat moss, sawdust, or sand in a cool place until
spring. These daturas generally prefer loose, sandy soils, somewhat on the dry side, and a sunny location. Those
native to the Southwest will stand considerable drought.
Harvesting:
The leaves and tops are preferably harvested when the plants are in full bloom, but they may be gathered at any
time from the appearance of flowers until frost. They should be stripped from the stem and dried as quickly as
possible. Fresh leaves have a fetid odor, which is lost on drying. Seeds harvested for psychoactive purposes are
collected by removing the capsules when they are ripe, but are still green and unopened. These are dried in the sun
or by low heat. Seeds for growing purposes should be gathered by collecting capsules that are just opening,
removing the seeds and drying in the sun.
(2) http://www.botanical.com/botanical/mgmh/t/thorna12.html#cul
Thornapple is easily cultivated, growing well in an ope, sunny situation. It will flourish in most moderately good soils, but will do best in a rich calcareous soil, or in a good sandy loam, with leaf mould added.
Seeds are sown in the open in May, in drills 3 feet apart, barely covered. Sow thinly, as the plants attain a good size and grow freely from seed. Thin out the young plants to a distance of 12 to 15 inches between each plant in the drill. From 10 to 15 lb. of seed to the acre should be allowed.
The soil should be kept free from weeds in the early stages, but the plants are so umbrageous and strong that they need little care later. If the summer is hot and dry, give a mulching of rotted cow-manure.
The plants may also be raised from seeds, sown in a hot-bed in February or March, or in April in boxes in a cool greenhouse, the seedlings, when large enough, being transferred to small pots, in which they are grown with as much light and air as possible till June, when they are planted in the open. Thornapple transplants readily.
If grown for leaf crop, the capsules should be picked off as soon as formed, as in a wind the spines tear the leaves. Some seed, for propagation purposes, should always be collected from plants kept specially for the purpose.
Stramonium seeds are official in a number of Pharmacopoeias. The thorny capsules are gathered from the plants when they are quite ripe, but still green. They should then be dried in the sun for a few days, when they will split open and the seeds can be readily shaken out. The seeds can then be dried, either in the sun or by artificial heat.
The dried, ripe seeds are dark brown or dull black in colour, flattened, kidney-shaped in outline, wrinkled and marked with small depressions, and average about 1/6 inch in length. Though ill-smelling when fresh, when dry they have a scarcely perceptible odour till crushed, but a bitter, oily taste. They should not be stored in a damp place, or will mildew. Kiln-dried seeds, it should be noted, are no use for cultivation.
(3) http://www.b-and-t-world-seeds.com/401249.htm
Datura Cultivation I:
Grow in full sun in moisture retentive but well drained fertile and preferably calcareous soil.
Propagate by seeds sown in situ in spring (16°C / 61°F) or earlier under glass and set out after danger of frost has passed.
The foliage is extremely susceptible to viruses affecting other Solanaceous plants and may act as a host . . .
Datura Cultivation II:
Datura seems to be an awkward genera in that it will often grow like a weed and at other times seems to resist every attempt at germination.
Datura seem to occur naturally on fertile wasteland, rubbish tips, dry river banks and roadsides - they almost always start growing where the ground has been recently disturbed (giving the seeds sheltered nooks where plant material can gather and rot, and where the humidity is maintained by being sheltered from direct sunlight and wind).
If similar conditions are reproduced Daturas can be very successful sown in-situ outdoors.
Aerial parts of perennial species die back during the winter (if frosted) and will grow back from the roots in spring.
The plants like full sun, in moisture-retentive, but well-drained fertile and calcareous soil. I tend to feed Daturas (and many other Solanaceae) with the same fertilisers I use for tomatos (these can be "chemical" or "Organic" according to your taste).
There seem to be 3 things that encourage good germination (Datura stramonium):
Temperature:
Ambiant temperature at about 70° F (21° C).
Light:
Sow with just a very thin sprinkle of sand or vermiculite on top of the seeds - experiments have produced results of 15% to 25% germination in the dark and 27% to 100% germination with some exposure to light (not direct sunlight as this will cook the seeds or burn the sprouts of those that germinate - the small plants must be gently introduced to full sunlight).
Humidity:
Covering the seed tray with a sheet of glass, or clingFilm will maintain the humidity. Propagating trays with clear plastic covers are also useful, they usually have air vents so that damping off can be prevented once germination commences.
Gibberellins (Gibberellic Acid-3 (GA-3)) have been found to stimulate germination amongst Daturas, but many growers prefer not to use them. Gibberellins are naturally produced by fungal action when leaves and other plant material decay - some compost or leaf mold blended with the seed mix may produce a similar effect.
Daturas are subject to statutory control as weeds in some countries (notably parts of Australia)
(4) From GLIDER (SPF):
D. Stramonium does not require stratification. Bottom
heat to 75-80 deg F and bright light should effectively germinate in less than 72 hours.