Create Your Own Rhododendrons
by Joe Harvey - May 2000
Rhododendron Hybrids
It is exhilarating, creating new life, as Mary Shelley described in her great novel. Confining yourself to new rhododendrons gets round most of the moral and practical problems encountered by her famous professor.
New cultivars are produced by deliberately cross-pollinating flowers and selecting the very best from any offspring that may result.
Unfortunately some flowers will readily self-pollinate and rhododendrons are among them. In these cases some precautions are necessary to prevent selfing.
Prevention of Self-Pollination
1. Removal of the corolla and stamens
Before the flower opens, using your fingers or small scissors,
cut off the petals and stamens, leaving only the stigma, style
and ovary. Generally speaking, once the corolla and stamens have been removed,
the flower loses its attraction to bees. The pollen is being shed as the
flower opens, but the stigma matures a few days later in most rhododendrons,
a condition called protandry – literally, the early male.
Therefore pollen from the chosen father can be dabbed on to the stigma a few days later and the flower labelled with a bread-bag.
There is a slight problem with this method in that the remaining flowers produce so much pollen that it can be spread around by wind and insects. By chance some may land on the stigma you have chosen for your hybrid. The effect is not big but it does happen. Rhododendron pollen is peculiar in that the grains are attached to each other in strings up to tens of thousands of grains long. You can see these strings as little ‘clothes lines’ hung between the anthers on opened flowers. Their purpose is to get entangled on the hairs on insects’ bodies but as they do so pieces of the ‘clothes lines’ may drop on to your stigma.
First cut some aluminium foil into squares a little less than 1 cm. on side. Then take a lead pencil and roll the foil around the sharpened end to produce a tiny cone. I usually produce a few dozen of these at a time.
Before the flower opens, tear apart the petals and pop a cone of foil over the stigma squeezing it to make it stick. You then have a guaranteed virgin stigma. (Please, no jokes about chastity belts.)
A few days later, take off the stigma cap, dab on your chosen pollen and recap the stigma with a fresh cone. Label the flower as usual with a bread bag tag.
The above method is by far the most reliable but requires a delicacy of touch not possessed by all. However I have used it with a high degree of success over the past 25 years.
The bread bag tags are convenient for writing the date, the female (seed) parent and the male (pollen) parent. Female always first. The polyethylene plastic will not mark with lead pencil and is too smooth for ball-point pens. What is required is a wax or ‘Chinagraph’ pencil in black. This is the sort of grease pencil that comes with a paper outer coat and a piece of thread down it to allow strips of paper to be successively peeled off as the lead is used up. (Those of you with children will know that this bit of thread is a magnet to kids.)
Possible seeds coming this fall include:
- pachysanthum x clementinae;
- pachysanthum x makinoi;
- degronianum ssp. heptamerum x gymnocarpum; and
- superdwarf tsariense x proteoides