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Question of the Week © 2017 Mike McGrath
Note: Hundreds of Mike's informative articles are available (in alphabetical order!) right here at the Gardens Alive website. To find Mike's answers to your specific garden problem, Click here and find your topic (like Weeds, Worms, Rhododendrons...) in our complete alphabetical archive of Questions of the Week.
Propagating a Perfect 'Prune Plum'
Q. I'm currently renting a house with an 'Italian prune tree' in the yard. We love these plums; they are delicious, and no one else seems to have this variety around here. We're thinking about buying a place of our own in the future—no move actually slated yet—but we don't want to lose out on these plums later down the road.
This tree sends up suckers all the time. Do you think it's possible to dig a few of those up, temporarily pot them, and eventually move them to our future new home? Would the suckers produce the same type of plum? Or are plums commonly a tree that is grafted? If so, would we be better off trying to propagate a cutting from the branches? I'm assuming that starting a tree from seed isn't a good idea as there are lots of ornamental plums around the neighborhood that our tree is likely 'breeding' with. Finally, regardless of the best way to 'transport' this tree, what's the best time of year to do the work?
---Sara in the suburbs of Portland, Oregon
A. There are a huge number of different types of plums. The "Italian prune plum" she talks about is almost certainly a specific variety of European plum whose fruits have a distinctive blue oval shape and a great taste whether you eat them fresh or dried into prunes. There are lots of other kinds of European plums as well; and in his classic book "Grow Fruit Naturally", our official man of fruit, Dr. Lee Reich, notes that European plums are among the tastiest types.
There are also Japanese plums, which like the European types, grow on small to medium sized trees; native American plums, which grow on plants that are more like shrubs; hybrids that combine the traits of Japanese and American types; and 'plumcots', which are hybrids of plums and apricots—some of which have been bred deliberately (including by the legendary Luther Burbank) and some of which have occurred naturally in the wild.
So Sara is correct that planting the seed—which is actually called a 'stone'—might not produce seedlings that are the same as her tree, especially since she notes the presence of other kinds of plums in her area. We have to assume that there could be some cross-pollination going on; which as we always like to explain, won't affect the fruits on the already growing plants but can change what the seeds will produce.
Now: What about her suckers?
Well, it turns out that you can grow a new tree from a sucker—a growth that shoots up next to the parent tree. But it's not easy. You have to get down there and remove a lot of soil, then sever the sucker with a lot of its own shoots attached and get it to root successfully somewhere else. But virtually all European plums are grafted trees; and so a sucker would grow the same variety as the rootstock and not the part of the tree that produces her tasty fruits.
That leaves either propagation by grafting—cutting one-year old stems that are called scions from the branches and attaching them to a rootstock—or rooting fresh 'softwood' cuttings from the tree directly in the Spring. Lee says she should try both methods—although scions that are grafted onto a different rootstock are probably going to do better long-term. And plums are one of the easiest trees to graft.
Lee says to collect the scions—sections of the tree that grew the previous season—while the tree is dormant, keep them moist and cold (which should not be a huge problem in Portland) and then graft them onto an appropriate rootstock in late winter or early Spring.
And, as we said, she could also (and/or) directly 'root' some fresh cuttings….
…which is the preferred method if you have a non-grafted plant. If this were a fig, for instance, you'd take a cutting, plant it in a pot of loose light soil-free mix, keep it watered and then plant it in its permanent location after it develops its own roots. In fact, figs root so easily that some people just plant the cuttings where they want the new trees to grow.
And a rooted cutting would produce the same plums they've been enjoying—but the smart money says that grafting will produce a better, healthier tree. Luckily, they have plenty of time to either find someone to do the actual grafting work for them or to research the techniques and choose the right rootstock for their conditions. And their Portland climate is going to be a huge help, as they can keep pots full of their newly-propagated trees outdoors over their mild winters. In the North, they'd have to be protected from winter cold.
And you know, their existing tree sure seems to be growing on the ideal rootstock for their conditions, so they might want to try using a newly emerged pencil-thin sucker as a rootstock; then they'd kind of recreate the exact same plant, top and bottom!