JARS v37n1 - Good News for Big Leaf Fanciers

Good News for Big Leaf Fanciers
Halvor Braafladt, Eureka, CA

Twenty years ago, as a beginning rhododendron enthusiast, I purchased my first big leaf rhododendron. It was a R. sinogrande seedling about 18 inches tall. It's impressive leaves kindled an enthusiastic interest for the Grande and Falconeri series which has continuously increased to the extent that I am now hybridizing them.
My enthusiasm for rhododendrons soon led me to communicate with Leonard Frisbie and the Pacific Rhododendron Society and soon I was raising species rhododendrons from seed. I began growing the seedlings in containers with the plan to select the better ones for a place in the garden.
In my readings on the big leaf rhododendrons, I soon learned that I must anticipate a prolonged period of years before blooming would take place. The ARS publication Rhododendrons for Your Garden seemed to indicate 15 to 20 years was to be expected in flowering from seed. Arthur Headlam wrote in the RHS Rhododendron Yearbook 1972 of a 44 year wait for the flowering of R. giganteum in Australia, however my experience in growing Falconeri and Grande species from seed has been much different as the following table will show.
This year there are two flower buds on the R. sinogrande I purchased from Druecker's Nursery twenty years ago and planted in a favored spot a few years later. In the interim I have flowered another Sinogrande in 12 years, grown from seed in a container, a R. giganteum in 10 years, a R. grande from 1972 seed in 7 years and a R. montroseanum , in 11 years. Companion seedlings planted in the ground are, in most cases, yet to bloom; several others, which were in containers 8-10 years before planting in the ground, flowered a year or two later than their container grown siblings.
The Falconeri series has averaged about the same length of time to reach flowering from seed. Below is a table of my results.

Growing Conditions:
Although a number of fertilizers have been tried, - Osmocote 14-14-14 is being used with two applications per year. All my other container plants have been watered by individual "spitters", (spray heads), on a drip system up to 2-3 times per week, since the drought 3 years ago.

In our mild climate the "big leafs" grow best in full morning sun despite the fact that an occasional hot spell, (the 80's in Eureka), will frequently sunburn the leaves of container plants but not those in the ground. Those plants grown in part shade are leggier and tend to have larger leaves. Planting big leafs after flowering can be expected to produce an interval of 2-3 years setback before flowering resumes despite the addition of superphosphate to the planting hole.

Based upon my experiences, the flowering of the Grande and Falconeri series appears to be accelerated by growing them in containers with the usual period being 10-11 years from seed. Growing "big leafs" in containers may produce stresses associated with repeated wetting and drying that accelerates flowering but also causes these plants to be more subject to sunburned leaves if exposed to full morning sun.
Hybridizing "big leafs" is now more practical. Growing big leafs in containers 8-10 years before planting in the ground seems to require a year or two longer to flower than if plants are grown continuously in containers.

Plant Seed Source, (if known) Flowered
R. arizelum ARS 72-11 Brodick 1982
R. arizelum ARS 71-225 KW # 20922 1982
R. basilicum ARS 67-165 1982
R. basilicum ARS 69-588 1982
R. coryphaeum ARS 67-440 Exbury (in ground) 1980
(container) 1981
R. eximium ARS 72-403 1982
R. eximium x ARS 72-467 1980
R. macabeanum ARS 67-70 1979
R. falconeri ARS 72-261 KW# 1982
R. falconeri ARS 67-42 (in ground) 1982
R. giganteum ARS 68-65 Bowman 1978
R. grande ARS 72-385 Sikkim 1979
R. grande ARS 68-69 Bowman 1982
R. macabeanum ARS 67-70 1979
R. montroseanum ARS 66 1977
(in ground) 1978
R. praestans
(prob hybrid)
ARS 66 (in ground) 1976
R. sidereum 1980
R. sinogrande var. Boreals Druecker 1962
R. sinogrande ARS67-20 Brodick 1979