Forced germination of aril iris seeds. Bob Nold Aril iris seeds can be germinated with the following technique. This method bypasses the need for any cold treatment. Materials for this procedure, shown clockwise: salt shaker, beakers, bleach, filter paper (coffee filters are fine), freezer bags, razor blade (note that this is a regular shaving-type blade, the edge not in use protected by masking tape), aril iris seeds. I prefer using non-chlorine bleach.
The aril iris seed. The yellowish portion of the seed is the aril, or collar.
Diagram of the seed. The seed has two ends; the chalazal end, and the micropylar end. Seeds of almost every plant species on earth germinate from the micropylar end. The forced germination procedure involves cutting across the micropyle, across the end of the endosperm and embryo, in order to create an artificial rupturing of the micropylar barrier, which in natural situations would be caused by exposure to cold, sometimes requiring years to achieve.
Seeds are soaked in a 10:1 water and bleach solution for a maximum of fifteen minutes. The purpose of this is to kill any bacteria on the seed coat. (Deno suggests this is not a necessary step.)
Seeds are rinsed in water to remove the bleach (an ordinary strainer works), and then soaked in plain water, with a tiny amount of dishwashing liquid (acting as a surfactant, to help wet the seed coat this is optional), for two to four days, in order to soften the seed coat for cutting. (The older the seed, the longer it needs to be soaked.) The water can be changed every day, if desired. I use salt shakers, with a label (masking tape) on each one, which helps identify the seeds, because they all look pretty much alike. Drain the seeds before cutting them, place on a paper towel, and cut the seeds. I use a watchmaker s loupe which allows me to see what I am doing..also aware that there is a razor blade close to my face. Use a razor blade designed for shaving; cover one edge, and most of the other edge, with masking tape, using just a small portion at the end for the slicing action.
Cut the seed just below the aril, using a slow slicing motion. It may take one or two or more passes with the razor blade, to expose the embryo. Be careful not to cut too deeply. Here are two not-very-focused pictures. This seed still has some of the aril attached. It will germinate. Here s another example. The tip of the embryo which has been sliced is the root end, and if just a tiny amount (1 mm or less) has been removed, no damage will occur. If too much has been removed, the embryo may be expelled by hydrostatic pressure within the seed. You can verify this by gently squeezing the seed; if the embryo retracts, it has been expelled, and will not germinate.
Seeds are put in a damp coffee filter, placed in a freezer bag, and put in a dark place at about 16C for a few days. The seeds should be inspected every day for germination, mold, or (not so common) the micropylar barrier will heal itself and the seed needs to be cut again. Make sure that the filters stay damp. Check for mold every day. I find it does not usually form before the seeds start to germinate. If some seeds are slow, those may be susceptible to mold or rot. If uncertain as to whether or not the seeds will germinate after about a week, squeeze them gently. They should still be firm. If not, they should be discarded. Some growers prefer to put the seeds into perlite immediately; either way is effective, so long as the seeds remain sufficiently moist.
Germinating seed. The embryo is emerging from the endosperm. At this point the seed can be left in the filter paper, to grow a bit more (important to watch for mold at this stage), or planted into pure perlite. The seed is best planted with the germinating embryo pointed down. This ensures greater contact with the moistened perlite.
The pots are placed in a propagator. Ventilators closed. Pots are lightly misted every day.
About a week later. This is just as satisfying as it looks. Some of the seeds will decide to grow backwards and fling their root into the air. The root can be sprinkled with perlite to keep it moist, or the seedling can be gently lifted and repositioned with the root growing down.
A few days later. The roots have begun to heave out of the soil, and the leaves (green part) are forming. At this point the seedlings can be transplanted into individual pots, with the roots covered, or left in the original pots.
About six weeks later. Iris seedlings growing in tree band pots in pure perlite. The tree band pots allow for a greater distance between the roots and the perched water table. Now that the seedlings have been firmly established in their pots, they can be left in the pots for the rest of their lives; however, care in summer can prove to be quite tricky owing to the perched water table which does not exist in the garden. My personal preference is to plant out the seedlings at the earliest opportunity (i.e., the following spring), and fed heavily. Irises in Section Oncocyclus and Section Regelia are heavy feeders and benefit from a regular feeding with a tomato fertilizer. If the irises are left in their pots, instead of planted out, a good rule would be to keep the seedlings only slightly moist during summer by misting, including a diluted water-soluble tomato fertilizer (they do not need to go dormant during
the summer, although summer dormancy is completely natural), and then once new growth begins, in autumn, to give them plenty of water and fertilizer until winter, at which point the seedlings should be placed in a sunny, but quite cool environment. When the next flush of growth begins, in mid-spring, the seedlings should again be given a great deal of water and fertilizer.