October 4, 2003: Jens Christian Birck spoke on this date at a Joint meeting of the Great lakes Chapter of the American Rhododendron Society and the Niagara and Toronto Chapters, Rhododendron Society of Canada. The following are notes from that meeting taken by Nicholas Yarmoshuk.
1. In nature Rhodos grow in full sun above the tree line. "There are no Chinese maidens standing over the plants with parasols offering shade. The sun is bright and strong as there are no trees to provide shade. But the air temperature is unlikely to exceed 80F. Strong light but low tempeatures result in compact growth.".
2. In nature in the high Mts. of China (and in other high regions where Rhodos grow in nature) air is very dry. Yet there is likely to be a fog in the early morning providing moisture to environment before it dries later in the day.
3. Little rain water falls on slopes in immediate area . . . . but there is still ample water for the rhododendron roots.
4. Water from the large catchment area at higher elevations drains along natural drainage courses to provide copious amount of water for plants growing at lower elevations.
5. Rhododendrons are best grown in Denmark in raw Swedish Peat Moss.
6. Swedish Peat Moss is much more course than chunky peat moss with lots of twigs and decaying plant parts and decaying woody plant parts.
7. NY comment: It, Swedish Peat Moss, which is exported to Japan and throughout Europe, seems to contain materials that would normally be found in our grow bark; i.e. decaying twigs and other very small pieces of wood. This suggests the presence of mycorrhiza in the peat moss that we would get from grow-bark.
8. Birck recommends that Rhodos be grown in full sun with no shade.
9. When growing in Peat, in summer, temperature at top of plant on the leaves may be at 40 deg C, (but the air temp is likely to be much lower) but the soil two inches below the surface will be at 18 deg C. This means that if the peat is moist, as it should be, there will be lot of transpiration fluid available for the plant.
Ed Note: In the mountains, where rhododendrons and azaleas are native plants, air temperatures may rarely exceed 80F and may fall to as low as 50F at night. Even though many varietes of rhododendron will be cold hardy to -20F the plants will succumb to the high heat both during the day and at night in southern Ontario's climate. It is likely that many of the Tigerstedt hybrids, while being cold hardy and which thrive in Finland, are difficult to grow in southern Ontario.
10. In winter, provide enough shade from south so that top of plants do not get heat stimulation. Plant parts below sun-strike level receive no direct sunlight. These parts remain dormant even on the brightest of days. Parts receiving heat stimulaton in the winter will experience die back because they try to grow and receive no water so they dry out. Therefore some protection is required to avoid sun hitting the tops of plants during those very cold days when the sky is clear and the sun is bright.
11. Water profusely in hot dry summer conditions so that peat moss is damp but not soggy. A fistful of Peat Moss, squeezed hard, should provide three or four drops of water, not be water logged so that water runs down one's arm from the fist-full of wet peat.
12. In Denmark, watering is not restricted but the cost of water is very high. Pricing structure of water supply in Danish cities appears to be identical to that in Canada which includes Water + Sewer + Operations + Delivery + Taxes.
13. Select for foliage, you get flowers for three week but greenery is for remaining 49.
14. Plant Lilies, hardy Cyclamen, both of which flourish in peat. He also mentioned a few others but I can't remember them.
15. Mulch with coarse peat moss . . . . roots grow up into the peat.
16. Fertilize in late fall because roots continue to grow even though tops do not.
17. Fertilizer . . . he uses any 1-2-3 ratio mixture of N-P-K with the addition of iron and some Sulfur.
18. He doesn't worry very much about the pH and doesn't have figures for that.
