Figs are a great fruit that’s mostly well-adapted to the south-eastern US, but they’ve got a major problem limiting them in our area: root-knot nematodes. Many of our soils are full of these microscopic parasitic worms that burrow into the roots of fig trees, sucking sap and impairing the roots’ ability to pull water and nutrients from the soil. In many cases a fig tree planted out here will just struggle along, making little growth and producing few or no figs, because of the constant damage to its roots from nematodes. This is also a significant problem in many other tropical and subtropical areas around the world.
Fortunately, there are over 800 species in the genus Ficus, and at least some of these fig relatives are resistant to nematodes, and some of those are graft-compatible with Ficus carica, the common edible fig. There has been some work done on this, but I’ve found that both the information and the plant species for root stocks are difficult to find.
I’ve compiled the reports I can find of what other people have done, and I’ve been doing some experimenting of my own. My goal is to find one or more species that grow extremely well in Florida, even in nematode-infested soil, and can be easily grafted to common fig, Ficus carica, with no incompatibility problems over the long term. For scions, I’ll use the fig varieties that are best adapted to growing and fruiting in our hot, humid climate. Since root-knot nematodes are a problem limiting fig cultivation in many tropical and subtropical areas around the world, an effective solution to this issue could have widespread applicability.
This is my first post on what I’ve learned. As I find out more, I’ll post updated information on this website.
Reports In The Literature
Much of what I can find in print and online about this subject seems to be people quoting each other. Of the two primary sources I can find, one is a 1925 report from the Florida State Horticultural Society, reporting on experiments successfully grafting figs onto two Ficus species as root stocks: Ficus glomerata, and an unidentified Ficus species from North Queensland, Australia.
The other is a paper published in 1970 in which researchers grafted figs onto four different Ficus species: Ficus glomerata (which is a synonym for Ficus racemosa), Ficus cocculifolia, Ficus gnaphalocarpa, and Ficus palmata. Both of these studies seem to have primarily investigated graft compatibility, and only secondarily reported some evidence of nematode resistance in the root stocks.
From what I can find online, two of the species tested in the second study, Ficus cocculifolia and Ficus gnaphalocarpa, are now considered synonyms for Ficus sycomorus, which is the “sycamore tree” mentioned numerous times in the Bible. Ficus sycomorus is native to tropical and subtropical semi-arid areas of Africa and in the neighboring Middle East. (Ficus gnaphalocarpa is now classed as Ficus sycomorus, subspecies gnaphalocarpa, native to Madagascar).
So all the root stock species tested in these studies boil down to just three species: Ficus glomerata, Ficus sycamorus, and Ficus palmata. (This doesn’t count the unidentified Ficus from Australia — there are 45 Ficus species native to Australia, and I’d love to figure out which was the one from the 1925 report, but that might be a substantial project.)
First off, Ficus sycomorus: The 1970 study referenced above found two forms of this species that seemed promising as potential fig root stocks, and a 2013 study found that sap from the roots of Ficus sycomorus had a powerful nematocidal effect under laboratory conditions.
I don’t have this species in my collection yet. I’ve heard of people growing it in Florida, and I’d love to get a hold of it to test both nematode resistance, and graft-compatibility with common fig. Do you have Ficus sycomorus (especially subspecies gnaphalocarpa), and would you be willing to donate some cuttings to me? Leave a comment.
***Update: The clone I acquired labelled as Ficus glomerata (described below), turns out to be probably misidentified, and is probably actually Ficus sycomorus.
Next, Ficus palmata. I got a start of this one several years ago, and I was excited to experiment with it, because it seemed the most promising rootstock candidate: it was reportedly nematode-resistant, and being particularly closely related to common fig, I figured it should be fully graft compatible. Also, it can handle temperatures dipping a number of degrees below freezing, so there shouldn’t be the danger of a tropical rootstock freezing out from under a cold-hardy fig tree, killing the top.
Unfortunately, I found that at least for the clone of Ficus palmata that I have, it’s turned out not to be nematode resistant — in fact, it seems perhaps even more susceptible to nematodes than Ficus carica. I planted out a number of ungrafted Ficus palmata plants in the ground in the spring of 2014, and was startled when most of them died over the summer of 2014. When I pulled up the corpses, the roots had the tell-tale swellings of severe nematode damage. I don’t know if there are multiple varieties of Ficus palmata, and perhaps some other types are resistant to this pest, or possibly the one I have is misidentified, but I can say that at least the clone I acquired under the name Ficus palmata is extremely sensitive to the kinds of nematodes in the soil here. I did graft a number of plants of this species with fig scions, and the grafts took well. But I don’t see a use for them in this area. (I gave plants of this type, both grafted with fig scions and un-grafted, to several people. If you got one of these, sorry!)
***Update: This clone, which I got as Ficus palmata, is likely something else. So my results probably don’t say anything about whether or not the true Ficus palmata is actually nematode resistant.
The next species is the one that’s had the most widespread sucessful use as a fig root stock: Ficus glomerata. I’ve got this species in my collection, and I’ve got experiments well under way with it. Years ago, on a visit to ECHO in Fort Myers, Florida, I got to see a mature fig tree in the ground which was grafted onto Ficus glomerata.
Ficus glomerata apparently worked well at ECHO, and so it seems to be a good fig root stock for southern Florida. Because it’s a tropical, special care must be taken in Central and North Florida to avoid the danger I mentioned above, of this frost-sensitive rootstock freezing out from under the frost-hardy fig tree grafted onto it. The tree would have to be grafted low, and the graft union covered with soil, to avoid this danger.
Several years ago, I tried this here in North Florida on a very small scale, planting out a single fig tree grafted onto Ficus glomerata. It grew well for two years, but had a problem with breaking winter dormancy too early, which killed it entirely in its second winter when a hard freeze hit the plant while it was pushing out new tender growth.
I don’t know how much the early breaking of dormancy was related to the root stock, or the fig variety (‘LSU Scott’s Black’, I think), or maybe the weather those two years was particularly erratic. It does seem reasonable that a tree grafted onto tropical root stock might be more inclined to push growth during winter warm spells than a tree on rootstock from an area that experiences winter freezes. If it turns out that this is a general problem on Ficus glomerata as root stock, one way around it might be to use fig varieties that are naturally late to break dormancy. I have noticed considerable variation on when different fig varieties break dormancy in spring.
A friend in Gainesville, Florida planted out another fig tree (of uncertain variety) grafted onto Ficus glomerata, and it grew and fruited well, but was subsequently removed for reasons unrelated to the tree’s performance.
I can confirm that the Ficus glomerata clone I have does indeed appear nematode-resistant: I’ve planted out non-grafted plants of Ficus glomerata in soil I knew to be nematode-infested, including right next to the Ficus palmata plants that got killed by the microscopic worms. The Ficus glomerata plants have thrived, and the roots I pulled and examined showed no sign of nematode damage.
I am propagating a number of plants of this species to try as a fig root stock on a much larger scale, with several different varieties of figs as scions, to see how the combination performs in this area. And I’ll try passing them to people further south in the state, to see how it does for them.
***Update: This clone, which I got labelled as Ficus glomerata, is probably actually Ficus sycomorus. I’m working to to figure out its true identity. Whatever species it is, it is graft-compatible with Ficus carica, appears to be nematode-resistant, and is very frost-sensitive, getting killed back at temperatures right around the freezing point.
Another species I want to try is kind of a wild-card. Ficus pumila is a type of Ficus with a very different growth habit than the ones mentioned so far: it grows as a vine. It has two distinct growth forms, a juvenile form and a mature form. In its juvenile form, it has tiny creeping viney stems, and numerous small leaves, with a growth habit clinging to walls or tree trunks. People sometimes use it as an ornamental, for this the ivy-like effect it gives to buildings or statues. But if the vines are not carefully trimmed back, they eventually transform into the mature phase of the plant, which has much fatter twigs and larger leaves, and reaches out from the surface it’s growing on, with stems dangling several feet out and down.
In the juvenile form of Ficus pumila, the stems are much too thin to graft onto, but the mature form has much fatter stems, fat enough to take a fig graft. Once a planting of Ficus pumila has started producing mature growth, it’s possible to root cuttings of this wood, which tends to retain this mature growth habit even once rooted. It should then be possible to try grafting fig scions onto the rooted cuttings.
Years ago, I asked a fig expert what he thought of this idea, and he said he knew of two different people who had done it successfully, both using cleft grafts. I don’t know what became of their trees.
Ficus pumila grows rampantly in this area, so I am assuming it is nematode resistant.
As of this writing (December 2015), I’ve got a number of rooted cuttings of mature-phase Ficus pumila. They’re still small, but as they grow large enough I’ll try grafting fig scions onto them, and plant them out in nematode-infested areas.
A major concern is that I don’t know how fat the trunk of a fig grafted onto Ficus pumila rootstock could get. Even on the mature phase of this species, the stems don’t seem to get thicker than maybe a third of an inch in diameter. They’d have to be capable of getting a lot fatter than that to support a fig tree. Maybe this would turn out to be a super-dwarfing root stock? I’ll let you know how it turns out.
Well, that’s the status of my knowledge and experiments so far on the subject of nematode-resistant root stocks for figs. I’ll write more updates as my work progresses, and as I learn more of what others have done. Hopefully I’ll hear from other people who have experimented with this topic and can shed more light on this subject. If have any information to add, please comment.