QBARS - v26n1 Boothii Series

Boothii Series
G. G. Nearing, Ramsey, New Jersey

Boothii is a series little used in hybridizing. It is mostly dwarf, lacking in hardiness. There are some very fine yellows and a couple of very fine whites. There really should be hybrids available from some of the best plants. Eventually, undoubtedly there will be; but so far there are very few. One is R. 'Bric-a-brac', a hybrid of R. leucaspis and R. moupinense . R. leucaspis is Boothii series and R. moupinense is Moupinense series. They are very similar and I treat them together. They are both dwarf and both have four stars in the British rating and are very little known in this country. I have had 'Bric-a-brac' in my nursery in the pit for many years. It is a very interesting rhododendron. It is not hardy but it has possibilities in it for crossing. It has very pretty flowers with dark stamens which contrast with the white and very interesting leaves which are oddly hairy. I have made crosses of R. 'Bric-a-brac' and have two that I have named. One of these is R. 'Cliff Spangle'. This is R. 'Bric-a-brac' crossed with pink R. mucronulatum . It began blooming in 1958. It is a very dwarf plant-still only six or eight inches high and a foot or so across and is a shapely plant but it has one very peculiar characteristic. The flowers always open about the first of April and, of course, that means the flowers get frozen. Every year it carries all its buds but when they have opened they usually get frozen.
This plant and its side partner, when an obviously frosty night is coming up, I throw a piece of plastic over the entire plant and in that way I have been able to get good flowering most years. Sometimes even under plastic the flowers will freeze. The other plant of this cross has exactly the same characteristics except that it is a totally different plant. It has entirely different leaf structure and is not nearly as dwarf. I thought it was going to be quite dwarf but last year it shot up and is about two feet high so it is just moderately dwarf. The flowers are not nearly as dark a color as R. 'Cliff Spangle' and the leaf and shape of the plant is entirely different. It is interesting to have plants of this Boothii and Moupinense series coming along. The second plant is named R. 'Cliff Garland'. These propagate fairly well from cuttings. There are practically no other hybrids of the Boothii and Moupinense series available in this climate. This shows that it can be done and I am hoping for more.
One of the Boothii series, R. sulfureum , which is a very fine yellow, is not a sulphur yellow as the name would suggest. It has had hybrid crosses in Europe. R. sulfureum has been crossed with R. flavidum to produce R. 'Yellow Hammer'. It has been crossed with R. moupinense to produce one called R. 'Golden Oriole' which I haven't seen. There are only a few possibilities for a good rich yellow in rhododendrons. I am hoping that since this hybridizing has been possible eventually someone will be able to take R. sulfureum with its yellow flowers and get the yellow into plants of this general type.
I have seen R. tephropeplum blooming and it is usually a poor color but there are some plants that run to a good shade of bright rose. I made attempts to cross R. tephropeplum years ago but did not get anything that was worth keeping, however, R. tephropeplum is a possibility in the better forms.
I have never had R. 'Yellow Hammer' but it is very well known in England. It is a good yellow and quite a popular plant. I am quite sure it is not hardy.
Another species, which I have had, is R. megeratum which is a yellow with very large, very rich brown stamens sticking way out from it which makes for a very startling effect. It is a dwarf like the others. I have two or three hybrids of R. megeratum but have lost my original plant. I have a cross of R. keiskei by R. megeratum which has not bloomed. I have a plant of R. pubescens by R. keiskei by R. megeratum which has a bud this year. I am hoping it will be able to carry the bud because, in a case like that, it may not be the cross. Very often with R. keiskei and its hybrids you cannot tell whether you have a cross or not. If I have a hybrid of R. megeratum then possibly I can go on further with it. R. megeratum is a very interesting plant in my opinion. It is not very hardy but many of the rhododendrons we deal with are not very hardy. Then there are R. chrysodoron and R. xanthostephanum of the Boothii series.
R. moupinense is such a fine plant in itself that it has been crossed very many times. It has been crossed with R. bullatum , R. carneum , and R. carolinianum . Hardgrove made a cross with R. carolinianum and I got a plant which blooms practically every year. It loses a few buds. I have been trying to get hybrids from it and maybe I have some somewhere but so far no obvious results. The hybrid is much like R. carolinianum but with much larger flowers, so that is what R. moupinense could contribute. R. carolinianum flowers are fairly small and R. moupinense are considerably larger. The plant itself is a good deal like R. carolinianum but you can tell it is not.
I have a cross of R. carolinianum by R. valentinianum for years and it still has not budded. Another cross is R. 'Seta' which is R. moupinense by R. spinuliferum . R. moupinense is given four stars in England. It is well worthwhile in itself and has great possibilities for hybridizing.