I’m converting sour plum trees into sweet plum trees by grafting

This large, sweet, yummy ‘Bruce’ plum is growing on a tree that used to make small, sour, unpleasant-flavored plums. Now it makes these big, luscious, sweet fruits, because I cut the top off the tree and grafted budwood from the good variety onto it. ‘Bruce’ has a wonderfully rich, complex, nuanced flavor – seriously, this is a plum that’s almost as good as a mango.

My property here in North Florida has lots of wild plum trees that grow like weeds and make huge quantities of fruit, but the fruits on these wild trees are sour and unpleasant-tasting. For the last several years, I’ve been experimenting with a technique to convert them into sweet-fruited plum varieties: each spring, I graft bud wood from good plum trees onto the sour-fruited wild native plum trees. Two potential advantages of this technique are that it lets the sweet varieties grow on a rootstock variety that’s supremely well-adapted to the local climate & soils, and it speeds the growth of the sweet varieties by providing them with a large, well-established root system.

The wild plum trees that pop up all over my property are probably flatwoods plum (Prunus umbellata) although they possibly they could be the closely related Chickasaw plum (Prunus angustifolia). Whatever species these are, they grow into small trees, ultimate reaching 15-20 feet (5-7 meters) if allowed to grow, and they send up lots of root suckers. They flower in January and February, and ripen fruit in May and June, with fruits that are small, extremely sour, and on some trees have some very unpleasant flavor notes.

I started my grafting experiments in 2014, inspired by my friend Oliver Moore who was grafting ‘Bruce’ plum onto the sour-fruited wild plum trees in his yard in Gainesville. ‘Bruce’ is a hybrid of the native Chickasaw plum crossed to Japanese plum species, and it has outstandingly delicious fruits.

The bark graft (aka rind graft) is easy: just cut the top off the existing tree, make a few cuts into the bark, slice the bottoms of your budwood twigs into wedges, and insert them into the bark (and bind them and cover to prevent from drying.) It gave me quick results: these budwood twigs had been fully dormant when I inserted them a week before the photo was taken, and just seven days later they were sprouting new growth. But I found this graft often had problems: the scions would grow for weeks or months, then get snapped off by a heavy wind, or just mysteriously die. I’ve since modified my plum-grafting technique.

Following Oliver’s example and using budwood twigs he supplied, I cut back a number of the wild plum trees on my property and grafted ‘Bruce’ plum onto them. I cut the budwood twigs in late winter, putting them in a plastic bag in the refrigerator for a few weeks to keep them in a dormant state. Once the rootstock trees started pushing out new growth in mid-March, I did the grafting.

Since I was trying to convert mature, large wild plum trees into sweet-fruited types, I first tried a graft that I had heard is especially well-suited to top-working big, mature trees: the bark graft, also called the rind graft. In this technique, you simply cut the top off the root stock tree with a horizontal cut, then insert a knife vertically into the bark, starting from the cut-off end, making a short vertical cut downward. Then you peel the bark back slightly from that cut, and insert a dormant twig from the scion tree that you’ve cut at the base into a long skinny wedge. Then you tie it up with rubber bands to hold everything securely together as it healed, and either paint over the graft with melted beeswax, or cover it with a plastic bag covered by a paper bag (the beeswax layer or plastic bag to prevent drying, the paper bag to prevent heat accumulation.)

Results were remarkably fast: in not much more than a week after grafting, the scions had new green leaves sprouting out, which rapidly grew into new shoots. But over the coming weeks and months, I noticed a pattern: the fatter the trunk I’d cut off and grafted onto, the worse the grafts did. Quite a number of of the twigs I bark-grafted onto large-diameter wild plum trees grew for a few weeks or months, then inexplicably died at random times. Or they would grow for a number of months, and then snap off on a windy day. I concluded that bark grafting, with the scion inserted into the bark right at the point where a large-diameter trunk has been cut off, seems to result in a structurally weak graft union, and it might have other problems causing the mysterious sudden deaths of the scions.

In the modified technique I’ve been using to graft sweet varieties onto sour wild plums, I choose smaller diameter stems to graft onto – one inch (2.5 cm) diameter or smaller. And I’ve been setting the graft a bit back from the cut off stem. Here’s what a successful graft done this way looks like two years later. (The branch coming off to the lower right is from the rootstock, so I need to trim that off.)

So I’ve modified my plum-grafting technique. Now, I graft onto smaller diameter wood one inch (2.5 cm) or smaller, and I’ve been setting the grafts into the bark a little back from the point where the wood was cut off. The graft style I’m using is complete guess on my part – I guess it’d be considered kind of a combination of bark grafting and T-budding. I make two cuts that together form a “T” as in T-budding, but instead of inserting a single bud, I insert a small twig of scion wood with several dormant buds, as in bark-grafting. I’m definitely not an expert grafter, and there are likely better ways to do this graft, but this technique does result in a number of takes for me.

So far, I’ve grafted four different plum cultivars onto the wild plum trees on my property. First one I tried was that excellent ‘Bruce’ plum. Another is ‘Guthrie’, a sweet-fruited cultivar of the native Chickasaw plum that was selected near Tallahassee, FL. Another variety came from friend of mine has a plum variety growing at his place that he says makes a nice tasting plums that are green when ripe. He doesn’t know if it has a cultivar name, so I’ve been grafting it onto my trees and just labeling it ‘Green Plum’. And finally, along a roadside near Newberry, Florida I found a group of wild plum trees with small, red, sweet delicious fruits, which are far superior to any other wild plums I’ve sampled locally. I’ve been grafting that one onto my trees, calling it “Newberry”. (I also dug some root-suckers, which I have in pots so I can plant out some own-root plants of this variety.)

I found a group of wild plum trees along a roadside near Newberry, Florida that make outstandingly delicious sweet, red fruits – much better than any other wild plum fruits I’ve sampled around here. I collected budwood twigs from the trees, and I’ve been grafting it onto my wild plum trees, labeling it variety, Newberry’.

So far, I’ve only gotten a few fruits from the plum scions I’ve grafted, but I expect increasing crops in the coming years, especially as I continue to add new varieties. Plums are notorious for pollinating well in some years and poorly in others. I’m hoping that by accumulating a large number of cultivars on the same property, there will be sufficient diversity in genes and flowering times that each good-fruiting type will have other compatible varieties around to pollinate it.

Plum trees happen to be what I have growing wild on my property, but most areas where trees can grow, a little searching will reveal trees growing wild that are graft-compatible with good food-producing fruit or nut trees. I encourage everyone interested in planting out food trees to first look at what they have growing already in their area – it might be possible that with a little work trimming and grafting, you can create an abundance of food from trees already there.

 


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