Dwarfing Mulberries: An Afternoon with Dr. A.J. Bullard

“Over here are the mulberries. This one is a pure Morus rubra that produces 2 inch fruits.” “Liza. Can you tell me what is different about this tree?”

This is the way of Dr. A.J. Bullard. He playfully taunts you with little snippets from his 70+ years of tree knowledge and then immediately follows it up by asking you seemingly impossible questions. “What is different about this tree?” 

Dr. A.J. Bullard isn’t a former horticultural professor, but a former baseball player and Dentist who is a botanical wiz. He reads botanical textbooks and then writes letters consisting of page upon page of single spaced revisions and fact checking to the authors. The most common complaint he voiced to me in reading these texts was how everyone seems to copy information from book to book rather than doing the research for themselves. Dr. Bullard is that man, the guy who has studied the intricacies of the Southeastern plant world so thoroughly and in real life that he often receives identification questions which have stumped the arboretums and universities (and he figures them out).

I didn’t know this about A.J when I went to visit him. I knew of him as the former president of the North American Fruit Explorers (NAFEX) who probably knows more about mulberries than anyone in the US. His knowledge is integral to the advancement of mulberries as a tree crop in the United States.

This blog post/essay is in relation to a running conversation about mulberries that I’ve had with A.J ever since we met (my boyfriend would tell you that I talk to A.J on the phone more than I talked to him when we first started dating).  The full conversation will be in the form of a presentation at this year’s annual NAFEX/NNGA conference in Tifton, Georgia. Among the multitudes of reasons why you should be there, hearing A.J. talk is one very, very good reason.


“What is different about this tree?” 

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Slowly, we approached the above pictured mulberry tree and he asks us again: “What is different about this mulberry tree?” I think on it for a bit and come up with nothing, so he asks again. “What do you see that is different with this tree?” I got nothing, A.J. No idea. “What about the height? It’s no taller than 12 feet,” he says. Ah, right…mulberries aren’t normally 12 feet tall unless they are a naturally dwarfing cultivar. “Correct!” “What if I told you this wasn’t a dwarf cultivar? What if I told you that I have figured out how to dwarf mulberries?”

Dear readers- Have you ever had your mind blown? It’s a flooding of immense realization and wonder and excitement, all at the same time. What I’m about to tell you not only blew my mind, but in a strange way paralleled my own exploits.

Dwarfing trees is a huge deal these days. Thousands and thousands of orchard acres are getting converted yearly into dwarfing orchards because 1.) more trees per acre=more fruit per acre 2.) smaller trees are easier and cheaper to manage/harvest. If you pick up an fruit industry magazine, there’s usually a very good chance of the magazine featuring one article on the promise of better dwarfing rootstock for pears/cherries/peaches/name fruit tree in the coming years because that’s where the industry is headed. However, there are some downsides to all of this and it’s usually in these three sectors: Costs (because trellis systems or support posts are expensive, Longevity (dwarfing rootstocks are shorter lived, maybe 25 years), and Input (these trees require tending from humans or else they’ll suffer and/or die).

What A.J has done to get dwarfing mulberries would allow an orchardist to fit close to 200 mulberry trees per acre. It costs less than, say, planting the same number of apple trees per acre on an m26 rootstock (semi-dwarfing) because the trees you plant are able to stand up without the need for support posts. They are longer lived (the trees pictured are 40 years old). And there are no chemical or water inputs necessary (other than establishment necessities).

Mulberry trees are naturally tall for fruit trees, usually around 30 feet or more (for M.alba and M.alba x M.rubra hybrids). Given the standard size, if you were to prune heavily every year, you could probably fit 70 trees per acre (more like 40 trees per acre if you didn’t prune heavily). With Dr. Bullard’s dwarfing methods, you could likely plant 3-5 times that amount per acre. Which, just to throw it out there, would be an incredible set up not only for people wanting to sell mulberries, but also for pastured chicken or pastured pork operations (more about that later).

Alright, so what goes into Bullard’s dwarfing methods? Note: What I’m about to discuss is only an hypothesis. We don’t know what is actually going on, but this is our best guess. Well, we think the name of the game is incompatibility. If you study the history of apple rootstocks like I have, it’s only a matter of time until you start to come across accounts of rootstocks (aka, the roots to which you graft your cultivar/scion/variety) imparting various characteristics into the cultivar/variety (here’s a fun essay on the subject I wrote last December). Some characteristics include a change in flavor, tree size, fruit size, disease resistance, yields, and death, among other things. Some of these characteristics (like death) are deemed incompatibilities. Keep this in mind.

Alright, so what did A.J do?

He took Morus alba (white mulberry- brought over from Russia in the 1600’s for silk production) and to it, he grafted Morus rubra (red mulberry-our native mulberry) or a rubra x alba hybrid. He planted the grafted trees in pots and let the rubra send out a vigorous shoot. Then he tightly wrapped a copper wire just above the graft union and buried the whole tree, leaving a small amount above ground. What grew up from there became a dwarf mulberry tree. Across the boards. At one point in time, he had an orchard of around 150 cultivars and he employed this method to fit them all into his yard. If you look at the above picture, you’ll see other dwarfed mulberry trees- all different cultivars.

He put the trees on their own roots using a method very similar to the one I made up 2 years ago (which you can read about in this essay). That’s part of the reason why my mind was blown, because I’ve been down this rabbit hole before with apples; only with A.J I got a chance to see a glimpse of what the future could possibly look like for my experiments. And also, there are major agricultural implications for this (a later essay).

Why does it work? We’re not totally sure, but we both think it could be some form of incompatibility transferred from the M. alba into the M.rubra which imbedded itself into the scion/variety/cultivar by the time the rootstock/nurse root girdled off and the tree was on it’s own roots. That incompatibility caused dwarfing. If you look at the ground where tree hits soil, you’ll see a bulge. Perhaps that’s where the vigor went.

Anyways- this is all very exciting and details of all of this, including how exactly to do it (which I’m doing as we speak) will happen this year at the NAFEX annual meeting in Tifton, Georgia.

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Rootstocks: Do they impact flavor?

Earlier this year, as I was doing some research on the effects of grafting apple varieties to Malus angustifolia (southern crabapple), I kept running across interesting accounts of noticeable changes to the apple varieties when grafted to crabapples. One of these changes is in flavor, which is what I’m writing about today.

This is the original snippet that sparked my interest. Why? Because this dude back in the 1800s is telling me that when he took the Bethlehemite apple, a dessert/culinary apple from Ohio, and grafted it to a crabapple rootstock, he got something different from the original variety. The grafted Bethlehemite apple had developed some astringency. Astringency is the key word here.

OMG, DID THIS GUY TURN A DESSERT APPLE INTO A CIDER APPLE BY GRAFTING IT ONTO A CRAB ROOTSTOCK?

This thought has rumbled around in my head for the better part of this year and whenever I had a moment to sit at the computer and not read my emails, I researched this topic a bit more. First, I went back in history (via google books) to find more testimonials of these findings. Here are a few:

1867:

1871:

1873:

1889:

 

I could go on, but there are many, many testimonials in favor of rootstock having a flavorful impact on the grafted variety. There were some naysayers, who basically just said “this can’t be so” and changed the subject. But all in all, my historical research has been in favor of a rootstock’s ability to change flavor in apple varieties.

Eager to pursue this topic, I started looking up scientific papers on the subject and started with this, Cornell’s research on nutrient uptake by different rootstocks.  The thoughts and questions of the horticulturalists back in the 1800s seem to still align with the questions of today, as seen in this conclusion:

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“The ability to match the nutritional requirements of a scion cultivar to a specially tuned rootstock…” COULD, in my opinion, create a cider apple out of a friggin’ dessert fruit.

Positive, I kept up the research and found considerable evidence in citrus fruit that rootstocks can change the flavor of the fruit. Here. Here. And Here.

This study, which looked at an apple rootstock’s impact on triterpene (cancer and immune disease prevention chemical compounds) found this:

“The largest differences in triterpene content were found between rootstocks. The results showed that both at harvest time, and after cold storage except the first harvest time samples, the apples from rootstock MM106 had significantly higher triterpene content compared with those from M9; … Selecting suitable rootstock might increase the triterpene content in apple peel in practice production.”

And this study on different rootstock’s impact on peaches showed that the variety ‘Suncrest’ on Julior (rootstock) and GF677 (rootstock), followed by Ishtara (rootstock), produced fruit with the greatest antioxidant activities and total phenolic contents. The ‘Suncrest’ on Citation (rootstock) and, especially, Barrier1 (rootstock) had reduced nutritional values of the fruit.

WHAT DOES THIS ALL MEAN? 

Right now, everyone I know who is planting a cider orchard is planting on known rootstocks like the MM series or the Geneva $eries. With these rootstocks, we know what size of tree we’ll get and we generally know when it will start cropping apples. This is valuable information because we want order and sense in our orchards. We also know the disease tolerances of each rootstock, which have been known to convey some resistance to the apple scion, and that’s all well and good. There are many knowns of these rootstocks because they’ve been extensively studied…for dessert fruit. But what about cider fruit? How many rootstocks have been thrown out in university trials for imparting astringency to an apple? Probably a lot. But what if this is what we’re after?!

If someone came to my farm peddling their wares and told me that they could take my dessert apple and turn it into a cider apple with one of their amazing magical rootstocks, I would buy it. I’m sure it would be a hit. This is why we have started in on the private research of grafting apple varieties to different rootstocks for the purpose of flavor/nutrient evaluation (as well as growth influences, which is another blog entry).

Currently, my partner and I have Malus angustifolia (southern crab), Malus baccata (Siberian crab), own-root, M7 and M111 trees grafted in our nursery to the same variety. These will soon get planted out at the farm in an area set up for evaluation. This, I believe, is another untouched frontier whose findings could be incredible for the future of growing superfruits, having value-added rootstocks, and growing with lower inputs.

So far, the science and the observations are there. There’s much more to learn, but why not start in on the fun?