Sea Buckthorn (Hippophae rhamnoidesis) a deeply dormant species that usually requires a stratification period of about 12 weeks (in refrigerator).  During that time, it’s happy to rest in some compost mix with a 10 to 12 percent moisture content at about 0-4⁰ Celsius (basically 33-39⁰ Fahrenheit), and it wants to have some air circulation, so it likes being in either a loosely twist-tied plastic bag or a zip-lock bag with about an inch unzipped to allow for some air exchange.  When it’s growing on its own, it wants to be somewhere between Zones 3a (like parts of Alaska and Minnesota) and 7b (Manhattan because of all the heat-generating large buildings, even though the NYBG’s Bronx location is in 7a).  A New York City climate is as warm as it will tolerate easily, therefore, so if you are south of the city, the plant may require special positioning when it is transplanted outside.

Although there are common time periods for pretreatment, many sea buckthorn seeds will simply be ready according to their own schedule.  Fluctuating pretreatment temperatures can often enhance germination results, but if the door of your refrigerator is opened frequently or for some other reason its inside temperature may regularly be higher, this may encourage the seeds to enter a secondary dormancy or display other unexpected behaviors, such as “early” germination.  The 12-week estimate is most common, but some seed lots can take much longer.  Those that are ready to plant will be plump and soft, otherwise pretreatment isn’t yet complete and should be restarted.  Even if conditions in your fridge meet the ideal standard, the seeds may just germinate when they’re ready to do so.  Some of your seeds may do it now, and others may take more time.  You might consider dividing the group of germinated seeds, planting half now and half later to ensure that at least some of them survive.

Germinated seeds can be planted in deep pots or plug trays in a good quality compost.  Keep them well watered and weed free for a year or two before you plant them in a permanent position.  They will grow much faster in the second year. 

Courtesy of the NYBG Plant Information Service