How to Germinate Difficult or Questionable Lots of Seed
F. W. Schumacher, Sandwich, Mass.
Many of us who have grown rhododendrons from seed for many years have learned that failure to germinate seeds of a certain lot on the first attempt may occur even with seed lots of unquestionable quality, while subsequent lots, more carefully tended, turned out to have germinated satisfactorily.
There, however, always exists the possibility, especially with seed lots from abroad, that quality may be impaired either by age or by exposure in transit. Such lots often will not respond to usual procedures.
If I fail to germinate a seed lot on my usual 'soil' mixture, two parts of shredded sphagnum moss and one part of perlite, or two parts of the former and one part of clear silica sand, I make a sowing on a bed of live sphagnum moss over these mixtures. The fresh moss is cut very fine with a pair of scissors and applied about an eighth of an inch thick.
If the moss is not cut fine enough, it will keep on growing faster than seedlings can develop. Even if applied thinly, it must be watched and undue growth cut down.
Seeding is done on this bed of moss and seeds are watered carefully into the moss, which retains moisture for quite some time and so is watered only when needed.
I had occasion this year to try this procedure again on a lot of Rhododendron yakushimanum seed as received from abroad. In two instances, when sown on the usual mixture, a few seedlings appeared, none in another instance. Two sowings made on live sphagnum, however, showed fair germination.
The best sphagnum moss for the purpose is not the kind that is found growing in water. This type is too coarse for the purpose and dries out too fast. The proper kind is found growing in patches in damp woods, or here on Cape Cod on the side of ditches in cranberry bogs. I keep a supply growing in an enameled pan over a few inches of peat in a cold pit. With every day watering, it grows at an astonishing rate and is a joy to behold, like a miniature pine forest with its bright green stems and foliage. Sphagnum moss occurs naturally among plants of many species growing at high altitudes and so is a natural seed bed.