Dear mailing list,
I have germinated about 5000 Zephyranthes pulchella, Z. smallii, Z. jonesii, and H. tubispathus seeds in each of the last two years, so here is how I do it and what I think is needed for optimal results. First, the mechanics: I use 6-inch plastic pots that I can set into a cut-off gallon milk jug. I fold paper towels three or four layers thick to cover the holes in the bottom of the pot, then put in 2.5-3 inches of sand, then about 1.5-2 inches of potting soil (the peaty stuff; I prefer Miracle-Gro for the micronutrients) supplemented with granular 20-20-20 NPK fertilizer at the rate of a small handful (sorry to be imprecise and nonreproducible, but the amount is not that critical) per 2 cubic feet. I cover the potting soil with another 0.5-1 inch of sand. I put the pot into a jug of water to soak up the sand and potting soil before adding seeds. Since I am looking for twins and off-types, I array the seeds onto the surface of the wet sand with tweezers, which ad
mittedly is inefficient but allows reliable recognition of twins. Then I sprinkle fine sand to a depth of 1-3 mm (up to 1/8th inch) over the seeds. The pots then sit in their milk jugs for 6-12 weeks on a greenhouse bench in full sun as the seeds germinate and grow to a suitable size for screening. At that time, I can dig out individuals of interest with my index finger and transplant them to soil in 6-inch pots. The soil that I use is typically a 1:2 or 1:3 mixture of sand and silt loam from a local corn field, mixed with granular 20:20:20 as above. I don't know the name of the soil series of the soil, but it is a highly productive Midwestern topsoil derived from loess.
By scrubbing out the pots and jugs before use, I have been able to avoid damping off more than 95% of the time. Once I a while I get a pathogenic fungus that can attack Zephyranthes seedlings. However, all of these species can tolerate damp soils, and Z. pulchella can be grown to maturity (flowering) on continuously waterlogged soil. I would have to be much more careful with more xeric species.
It is important to wet both surfaces of the seed, hence covering them helps. However, I suspect that germination also requires light, so I use light-colored sand and don't bury them too deeply. On the other hand, if the covering is too shallow, the growing root will heave the base of the hypocotyl above the sand surface, which inhibits further growth. Sometimes I sprinkle additional sand onto such germinants to bury the basal plate below the surface.
I check the jugs for water every day or two, especially in hot weather. The peaty layer helps to hold water, so the surface dries less readily than it would with sand only. Continuously wet peat is a good environment for denitrifying bacteria, and thus these seedlings will run out of nitrogen after three months or so. They should be transferred to soil before this happens, especially if flowering is desired the next year.
The seeds of all of these species are relatively short-lived. The three Zephyranthes are ready to germinate immediately and are best planted fresh. The Habranthus requires after-ripening by drying out for about five days, then rehydration for germination. Germination of the Zephyranthes is slowed if they dry out for the same duration. However, my schedule usually requires me to dry the seeds of all of these out and then store them at -20 degrees Celsius (-4 degrees Fahrenheit) until I can plant them. I store the seeds in coin envelopes. I suspect that freezing at -20 would kill seeds that have not been dried.
So far I have been able to keep Stagonospora curtisii out of the greenhouse. However, Zephyranthes tolerates tebuconazole well, and that is an effective systemic control.
I hope that this information helps.
Charles Crane
Department of Botany and Plant Pathology
Purdue University
915 W. State Street
West Lafayette, IN 47907-2054