Time for a long-overdue update on my project to explore potentially nematode-resistant fig rootstocks. The project hasn’t progressed as fast as I would have liked, but I do have some potentially promising results with the Ficus species I rated as a “wildcard” in my first post on this topic: creeping fig, Ficus pumila.
To recap, common fig, Ficus carica, is an excellent fruit tree for warm climates, but one major factor restricting its production in many areas is root-knot nematodes. These are tiny microscopic worms in the soil that damage the roots of fig trees, impairing their ability to pull water and nutrients from the soil.
Common fig has many cousins in the genus Ficus. If we can find one of those cousins that’s both resistant to root-knot nematodes and graft-compatible with common fig, it could be a rootstock that would enable growing fig trees in nematode-infested areas.
I had heard reports that people had successfully grafted Ficus carica onto creeping fig, Ficus pumila, and creeping fig appears to be nematode-resistant, so I decided to try it.
This is a bit challenging because of creeping fig’s growth habit: it grows as a vine, with two distinct growth forms. The juvenile form has tiny stems, too small to graft onto. The mature form has larger diameter stems, but they usually only appear above many feet of the juvenile form, climbing a wall or trunk of another tree.
In order to have plants of Ficus pumila with stems with a large enough diameter to graft onto, I first rooted cuttings of the mature phase of creeping fig. Once I had several plants successfully rooted, I grafted common fig, Ficus carica, onto two of them, using a cleft graft. I’m not sure of the variety of common fig – it was from a plant I’d acquired that was supposed to be “LSU Purple”, and that’s what I thought it was at the time I did this grafting, but turned out to be mis-labeled, so the actual fig variety is uncertain.
That was in the spring of 2016, and the grafted plants grew over the course of the rest of the year, still in pots. At first they were very floppy, needing staking, which is what I would have expected from grafting onto vine. But over time, the Ficus carica stem below the graft on each plant has strengthened to the point that they probably don’t need staking any more (I’ll keep them staked for a while just to be sure).
The two grafted plants appear healthy, and both made a crop of figs in 2017. I’ve been checking the graft unions for signs of swelling, which could indicate potential delayed graft incompatibility. One plant shows no swelling, the other has minor swelling, small enough that it’s hard to tell if it’s a sign of incompatibility (sometimes healthy grafts show slight swelling).
I planted one of the two plants in the ground in the late summer of 2017. As of this writing (October 2017) the other plant is still in a pot.
One thing I had wondered about is the size discrepancy between the two species. Ficus carica can have a tree-trunk at least six inches (15 cm) in diameter, while Ficus pumila stems tend to be much smaller. In my first post on this, the fattest stems I’d ever seen on Ficus pumila were about a third of an inch (.7 cm), and I had wondered what happens when you graft a fat-trunk species of tree onto a narrow-trunk species of vine. Since then I’ve encountered Ficus pumila plants with stems about 1.5 inches (3.8 cm) in diameter – large enough to allow a fig tree to grow into at least moderate size.
I had wondered if possibly Ficus pumila might turn out to be a dwarfing root stock for figs. It might take several years to confirm this possibility or not. To really decide if there is a dwarfing effect, I should plant out a number of plants of the same varieties of fig, both on their own roots and grafted onto Ficus pumila. Right now, the two grafted plants are both about 30 inches (76 cm) tall.