The following guide was written by Emma Frawley, my former student and the pre-eminent grower of little barley. This guide pertains to growing little barley in a controlled setting (a greenhouse or growth chamber). My own notes on growing little barley outdoors will be added soon!
It is important to note that the timeframe for growing little barley in a controlled setting, from start to finish, takes places over nine to eleven months – only minimally shorter than the species’ natural annual growing season. It is possible that this window can be refined down to an even shorter period with more intensively controlled germination and growth experiments – i.e., to find the minimum amount of time necessary for after-ripening, growth, and a cold treatment to still produce seed.
Collection and after-ripening
Little barley is a weed through and through – mimicking its natural life cycle is the best way to reliably germinate and grow seedlings in a greenhouse or other controlled setting. After collecting wild seed in the late spring and early summer, seed must be after-ripened (stored) at room temperature for approximately 3 to 5 months before planting in soil. I recommend collecting and storing the seed in coin envelopes. I had the most success letting seed sit from mid-May to late-September, a window of 4 to 4.5 months. In my personal experience, the following treatments did nothing to enhance germination or seedling growth: freezer storage of the seed; removal of the glumes, lemma, and palea; scarification with sandpaper; gibberellic acid and potassium nitrate solution; liquid smoke, hydrogen peroxide; 37° C oven; or 57° oven. After-ripening the whole planting unit at room temperature is the best, and perhaps only, germination requirement.
Sowing
After the after-ripening window, I recommend planting seed in 4-inch-deep cell trays using moistened Arabidopsis soil mix (either metromix 350 or other peat moss-based mix (1:1:1 perlite, fine vermiculite, and sphagnum moss)). Sow the seeds only a few centimeters below the surface and then lightly cover with soil. Immediately after planting, dome the trays to trap moisture. It is not necessary to place the trays underneath a mist bench. Once the seedlings begin to germinate, roughly 10 to 25 days after planting, remove the domes.
Growth
The little barley seedlings will grow to fill as much space as they are given in approximately one to two months. Around this timeframe, it is possible to collect tissue off the plants for DNA extraction without disrupting the growth habit. The plants will be surprisingly robust in the 4” cells. It is possible to transplant the seedlings into larger pots around this stage, but I do not find it necessary. After one to two months of growth, little barley will need to undergo a cold treatment to flower and set seed, as is standard for winter annuals.
Cold treatment
I recommend placing the little barley in a designated “cold greenhouse” or a growth chamber at 10°C (50°F) for 8 hours and 15°C (59°F) for 16 hours for two to six weeks, with at least three weeks as an optimum. It is possible to expose little barley to even colder temperatures, such as down to 4°C (39.2° F) for 24 hours a day. However, I did not find a significant difference in seed yield between the milder (10°/15°) and colder (4°) temperatures. Placing little barley outdoors during the wintertime will likely induce a similar response, though I have not tested this myself.
Re-introduction to greenhouse
After a cold treatment for two to six weeks, the little barley can be placed back into the greenhouse. It is possible to gradually warm the growth chamber back to greenhouse temperatures to minimize shock, but I find that little barley is hardy, and this process is not necessary. Approximately one to two months after the cold treatment the little barley should begin to produce inflorescences. Within days to weeks the inflorescences will produce flowers, and within another month they will produce seed.