When we look at the huge range of different trees and shrubs available for our gardens, we take it as a given that something new is always coming along – the latest variety of rose, like the arrival of the Knockout Rose, or the exciting twice-blooming Encore Azaleas. Like the latest models of our phones and computers, we see this as a normal thing, and rarely ask ourselves where these plants come from. Unlike that new phone, almost all were certainly not invented and developed by applying the latest technological thinking – although a few do involve innovative techniques. The vast majority of new plants we have came about in exactly the same way they always have, by the careful and time-consuming process of searching for variations among many individual plants.
What is a Plant Variety?
Even this term can cause confusion. All living things on the planet belong to individual species – natural groups of similar individuals who breed together, or at least could do so. These are the things that have those double-barreled names in Latin, like Quercus rubra, for the red oak. Species can cover large areas of a country, or even of the globe, and of course the individuals closest together are the ones breeding together. This can lead to local variations in size, leaf color, flowers, and other minor changes that may lead botanists to call one of these different local groups a variety. These names have the abbreviation ‘var.’ in them, like Quercus rubra var. ambigua. This is a local, slightly different red oak growing wild in the north-east. Occasional individual plants found with some minor difference are sometimes called forma, abbreviated to ‘f.’, such as Quercus rubra f. juvenilis. Many of these variety and form names are today considered confusing and unnecessary. Often they have been absorbed back into the main species name. All 29 different varieties and forms of red oak that have been named are now generally considered to just be the one, same species – red oak.
What is interesting about these botanical varieties is that they show us how different one individual plant can be from another. Gardeners may not notice this, because when we buy a dozen of the same plant, they are often literally the same plant, just turned into new individuals by growing them from cuttings or grafting. Seedling plants, on the other hand, are always going to be different from their parents, just as our children are different from us. That natural variation is the source of almost all of our ‘garden varieties’ of plants, which we should, to be precise, call a cultivar. This useful term makes it easy for us to distinguish natural, botanical varieties from specially selected garden forms, and is the word used by most professional landscapers and designers. Cultivar names are those names in single quotes after the Latin name, like Quercus rubra ‘Splendens’, a tree with exceptional fall color.
Finding New, Interesting Plants
When we look closely at many plants, all of the same species, grown from seed, we see these individual variations. Some might be interesting enough, a different flower color for instance, that we want to grow them in our gardens. Almost every garden variety is just that – an unusual individual picked out from a large group of seedlings. These might have come to us by several different routes:
- Found growing in the wild – if you spend a lot of time wandering the hills or forests, looking at plants, once in a while you will find on that is interestingly different. Bring it home, grow some new plants from it, and you have a new cultivar you are free to name after your spouse, your dog or yourself. If other gardeners agree with you, it could go on to be widely grown.
- Found in a batch of seedlings – this is probably the most common way cultivars come about. Someone grew some seedlings of a particular plant, and one individual plant stood out as different, and was ‘taken aside’, reproduced, tested and named. This could have been a deliberate attempt to make something new, but often it is just chance – and a sharp eye.
Increasing the Chances of Variation
These natural variations are very rare, and hard to find – you might need to grow thousands and thousands of plants to find just one. So to increase the chances, plant breeders create hybrids. These are plants that come from the transfer of pollen to seed between two plants of two different species, almost always between plants of the same genus. The genus is the first word of the two-word Latin name, for example, Quercus. In animals this is very rare, but in plants it is much more common, so for example there is the Bimundors Oak, a hybrid between White Oak and English Oak, grown for its profuse acorn crop for wildlife. It has an ‘x’ in the name, to show its hybrid origin, so it is Quercus x bimundorum, although it might also have been called Quercus alba x robur.
Once you hybridize two different species, you release a flood of variation, and every seedling from the same cross is often different and interesting enough to end up being a new cultivar. These hybrids could be accidental, such as the cross that gave us the Leyland Cypress, or it could be deliberate, from the hand of an amateur or professional plant breeder.
Sometimes, to increase the chances of getting something specific, breeders use already-existing cultivars, and they can get several worthwhile new plants from the batch of seeds from a single crossing. For example, in the Girl Series of Magnolias, six of the eight cultivars in the series, all with differently colored flowers, came from a single cross between a flower of Magnolia liliiflora ‘Nigra’ and a flower of Magnolia stellata ‘Rosea’. Mind you, the breeders still had to grow hundreds of seedlings to flowering size – a wait that typically takes about 10 years for magnolias. If not happy with the results, its back to the greenhouse. No wonder we value our magnolia cultivars!
Now the Ball is Rolling
Once you have a supply of different cultivars and hybrids to work with, you can really go to town, as for example rose breeders do. By making many different crosses between existing interesting plants, and maybe bringing in some new, rare species as well, breeders get hundreds of different new plants. A good ‘eye’ is important, as a seedling with its first bloom can be unimpressive, but if potential is seen it will be grown for a few years to test it out, and could soon be for sale on a website near you. After a while, showing in the name where it came from gets too complex, so with groups of plants that have many different cultivars involving many species, we keep it simple and just call the new plant Rosa ‘Peace’, or whatever name it has been given. Hopefully somewhere there will be a record of the details.
All this work by dedicated plant breeders over the last decades and centuries has given us thousands of plants to choose from. When we grow them, let’s spare a thought for those breeders and selectors, and the legacy of their work to bring so much beauty and joy into our gardens.