After a day in Chicago we headed out to Red Fern Farm in Iowa just west of the Mississippi on July 16th. I stayed for three days and never learned so much in such a short time. Tom and Kathy Wahl have been planting Chestnut trees there about 30 years ago and since planted and interplanted mainly with Pawpaws, Walnuts and relative Juglans ssp., Honeyberries, Cornelian Cherries and Grapes. Next to these main crops they are growing almost every fruit and nut that can grow in hardiness zone 5 and the continental climate they live in. Tom challenged me to name any hardy fruit or nut as he was sure he would have it growing in their polyculture. After many tries I was able to come up with Ginkgo nuts and Rosa rugosa fruit which he hadn't tried yet but was aware of.
All the fruits and nuts at Red Fern Farm are harvested in a pick-yourself system by the customers, who are sometimes willing to drive long distances for them. Chestnuts don't seem to be a good market with anglo-American people, who make only 1 % of the customers. The main customers for Chestnuts are Bosnian and Chinese people. The Pawpaws on the other hand are harvested around 60 % by anglo-Americans, still not as high as the proportion of anglo-Americans in the area as I would guess. The chestnuts are sold for 3 $ per pound (~ 6,6 € per kg) but the price will go up to 3,5 $ soon, as prices are going up everywhere.
Tom got interested in growing Chestnuts by the fact that the American Chestnut once was feeding the American people as a staple crop and is now on the verge of extinction because of the Chestnut Blight. Hearing that the Chinese Chestnut is resistant to the disease and by crossing the American with the Chinese Chestnut this tree could once again feed the people in a perennial and sustainable way he started planting chestnut trees. Then after hearing about Permaculture and reading the Designers Manual by Bill Mollison, Tom and Kathy began creating a diverse polyculture of woody plants and herbaceous perennials.
The walnut and chestnut trees are planted at a spacing of 20x20 feet (6 m) and are thinned out to 40x40 feet (12 m), removing three quarters of the trees, when the crowns start touching each other. As the soil is a fayette loess soil, one of the best soils in the world, the trees will probably grow very tall and Tom plans on thinning out to 80x80 feet (24 m) eventually and will leave a note for someone to thin out to 160x160 feet if the trees will ever grow as big as "il Castagno dei Cento Cavalli" (the Chestnut of a hundred horses) in Sicily, Italy.
To decide which trees to keep and which ones to thin out, he uses a color marking which he sprays on the trees every year to keep track of which trees had no, bad, medium, good or very good yield. Trees with all blue markings are reliably yielding, ones with only red or orange markings are not productive and are thinned out. When good trees stand next to each other he may thin out the neighbouring trees, so the end pattern may not be symmetrical. When only bad ones are standing next to each other he may replant new trees in empty areas.
Tom was experimenting with all kinds of different planting strategies over the years. He tried using cardboard and wood chip mulch but the cardboard has to be renewed every year or weeds would grow through. He also tried landscape fabric which is hard to remove after some years. Nowadays he uses Oust herbicide to suppress the weeds under establishing trees. Next to some trees I could find some very happy looking living mulch comfrey plants. Comfrey has a deep taproot and not much siderooting and thereby doesn't compete much with tree roots and it is good at suppressing grass which can outcompete young tree roots. Tom also tried Rhubarb and Horseradish which weren't very successfull in the long term but can still be found here and there together with Asparagus.
Tom is also very convinced of using tree shelters. The tree shelters are 5 feet (1,5 m) high and have ventilation slits. Without ventilation the trees would die in the summer heat. Tom states the tree shelters reduce the mortability of the trees, set the side branching height to 5 feet, dramatically increase growth rate to the point that fruiting may occur 5 years earlier than without a shelter and protect the trees from browsing of deer and rabbits. Once the trees get too girthy for the shelter it is removed and a short piece of drain pipe is put around the trees to protect them from antler rubbing by deers. The deers only rub their antlers very low. To deal with voles, they keep the grass mowed short so that predators like hawks, owls, coyotes and badgers can catch the voles and they have less housing opportunities.
They are lucky to not have any chestnut weevil present in the region. It is hard to deal with the chestnut weevil in an organic approach, Toms suggestion to keep the population low is to pick all ripe nuts from the ground every day and let pigs roam around after the harvesting season and chickens in spring when the adult weevils emerge from the ground.
The Chestnut trees which got planted years ago got a subsequent ecto-mycorrhiza inoculation using a self made syringe to apply right next to the roots.
It was very interesting for me to hear that they are almost only growing Chinese chestnuts (Castanea mollissima) or hybrids with the American chestnut (Castanea dentata) but just very few species or hybrids of European (Castanea sativa) or Japanese chestnuts (Castanea crenata). The European chestnut is also susceptible to the chestnut blight, but other than in the USA, in Europe hybrids with Japanese chestnuts are very common. European varieties with french and spanish names like 'Bouche de Betizac', 'Marigoule', 'Précoce Migoule', 'Dorée de Lyon' or 'Marsol' are all hybrids between European and Japanese chestnut. In America on the other hand hybrids between the American and Chinese chestnut are more prevalent. There are not many Japanese x American hybrids or European x Chinese hybrids.
Tom prefers the Chinese (x American) varieties because the skin hull is not as bitter and fuzzy as with the European (x Japanese) varieties. Therefore the Chinese chestnuts can be eaten raw, without peeling. But also the skin peels better as the Chinese chestnuts are not as indentated as the European. He also claims that they taste much better. So I am very interested now in trying to source these varieties in Europe or trying to bring them there. Also where are the European x Chinese varieties and how would they taste and peel? By the way, the 'Dunstan' chestnut, often claimed to be a resistant American variety, is almost completely Chinese with maybe a hint of American in it.
Also Tom explained to me why many Chinese x American hybrids are pollen-sterile. The Chinese chestnut seems to have a pollen-fetility related gene on the mitochondrial DNA which is only passed on by the female, so when crossing a male Chinese a female American, half of them will be pollen-sterile. Pollen-sterile hybrids don't make pollen at all and thereby can't fertilize other chestnuts to set fruit. It is like having a pollen-sterile triploid apple variety. If you have one pollen-sterile plant you will need at least three plants (two of them pollen-fertile) to have all three plants fruiting. Many of the European x Japese hybrids are also pollen-sterile, probably because one of them (Tom guesses it might be the Japanese) also has a pollen related gene on the mitochondrial DNA.
Next to most of the Chinese varieties like 'Qing', 'Peach', 'Gideon', 'Auburn Super', 'Sleeping Giant' (Cx(JxA)), 'Nanjing Special', 'Kurakata Sweet' (CxJ), 'Amy', 'Mossbarger', 'Jenny' and 'Luvall's Monster', Tom and Kathy are also breeding their own varieties: 'Shotgun', 'Red Fern Super', 'Hoben #1', 'Hoben #2', 'Gandalf', 'Elrond', 'Treebeard', 'Igor' (named after a person in Russia who doesn't have his own garden but wants to be involved in plants and sends Tom plant material without having ever met him in person or being to the farm), 'Sandy', 'Mark', 'Phil', 'Mike', 'Ken' (CxA), 'Terminus', 'Apex', 'Kaching', 'Arthor Radley', 'Jem', 'Atticus', 'Scout', 'Tucker', 'Giant Badger I' (CxA), 'Giant Badger II' (CxA), 'Large Badger I' (CxA), 'Large Badger II' (CxA), 'Large Badger III' (CxA), 'Badgerqing I' (CxA), 'Badgerqing II' (CxA), 'Badgerqing III' (CxA), 'Qingsu' (the most productive of all their varieties), 'Type AB+' (CxA), 'Arbor Laedi' (formerly called 'Broken Tree' but the latin name sound much nicer, this tree had such a heavy yield that the branches started to break from the weight) and 'Resilient'. Chinese varieties he didn't list but are also common named varieties include: 'Kohr', 'Perry', 'Payne', 'Ace', 'Knitzel', 'Hong Kong', 'Szego' and 'AU Homestead'. To keep track of the varieties they are labeled with a lifestock eartag pen, which is very weather resistant, on a PVC pipe.
The second most important crop next to the ~ 1.200 chestnut trees are the several hundred of pawpaw shrubs between the chestnuts. The pawpaws grow as fast in shade as they do in sun but they fruit much better when not standing in full shade so the yield may decrease once the chestnuts overshadow them completely. Pawpaws (Asimina triloba) are the only hardy member of the Annonaceae family, which include tropical fruits like custard-apple and cherimoya, and pawpaws taste as tropical but are hardy almost down to zone 4, one of Toms breeding goals is to select for even more hardy pawpaws.
Pawpaws make root suckers and form dense patches after some years. Pawpaws are self-sterile so there need to be two plants with different genetics to make fruit. What is strange is that pawpaws surround themselves with their own genetics by making patches of suckers and also they are pollinated by flies and beetles which don't travel as far as bees do, a recommended spacing between fertilizing pawpaws is 8-10 feet (2,5-3 m), max. 30 feet (10 m). So in the wild you will often find many pawpaw shrubs but no fruit at all because all trees are clones of each other. But sometimes when two patches grow together there can be a heavy fruit yield.
Pawpaws can be grafted but are almost impossible to root cuttings from. Grafted trees fruit after about 3-4 years while ungrafted ones take about 7-8 years. Normally seedlings of pawpaws also make good fruit, so selecting new varieties can be very rewarding. 'Summer Delight' is the earliest of all pawpaws that Tom and Kathy are growing, 'Sundog' is a variety from Red Fern Farm that is tested for self-fertility. There are some varieties like 'Sunflower', 'PA-Golden 1', 'Prima 1216-60', 'Balda' and 'Gorini' which are also speculated to be self-fertile, but Tom could only confirm 'Sundog' so far. 'Canopis' is their most productive pawpaw which ripens late. 'Hypro' is also very productive and the fruit of 'Iowa Golden' all ripen at the same time and have strong yellow color break which makes it easier to tell when they are ripe. Normally the ripening period of one pawpaw variety expands on about 3 weeks. With different varieties this can be extended much more.
To bring pawpaw seeds to sprouting Tom separates them from the fruit pulp as soon as they are ripe, stratifies them (maybe not even necessary) and then keeps them very moist and very warm at 90° F (32 °C) until they sprout (about 2 weeks).
The sheep at Red Fern Farm eat walnut leaves and chestnut leaves and all kinds of green but won't touch pawpaw leaves at all. The only animal that seems to eat the leaves at the farm is the zebra swallowtail, which depends on the pawpaw leaves as it's only food source.
To sustain a harvest of heartnuts and walnuts Tom and Kathy have to set up traps against squirrels as without the traps there will be no heartnut harvest at all. They eat them unripe on the tree and leave none ripening. Also some of walnut trees develop a bunching disease which is caused by zinc-deficiency, so they apply zinc under affected trees. Over the years they have experimented with many plants growing under walnut trees and discovered that mainly plants from the Rosaceae family seem to have a problem with the juglon exudated by walnut roots and through breakdown of leaves and husks. Tom says that black currant doesn't mind growing under walnuts and Vivian Böllersen mentions cherries, nectarines, peaches, plums and black raspberries in her book "the revival of the walnut" (german book). Tom also observed that persimmons, pawpaws or chestnuts don't seem to have a problem growing near or under walnut trees at all. Also it is mainly the black walnut (Juglans nigra), which exudates about 10 times more juglon than other Juglans spp., that is of concern in this matter.
The persimmons they grow are all American persimmon (Diospyros virginiana) as hybrids with the Oriental Persimmon (Diospyros kaki) are not hardy enough in zone 5. The only hybrid that survived a winter so far is 'Chuchupaka'. Other varieties they grow are 'Yates', 'Prok', 'Geneva Long', 'Osage', 'H69A', 'H120', 'A118', 'A120', 'Morris Burton', 'H63A', WS810', 'Sophies Gift', 'Pine', 'Rosy' (male), 'Szukis' (male), 'Wapello' (female), 'Wapello' (male), 'Arboretum' (female), 'Arboretum' (male) and 'Evelyn'.
They don't grow hazelnuts as American hazelnuts are not falling out of their husk and therefore need even one more processing step in addition to the other steps they alteady need. The European hazelnut is susceptible to the filbert blight disease which is present in North America and makes the cultivation of European hazelnuts (which fall out of their husk) impossible there. Maybe a hybrid might be resistant and falling out the husk. Mark Shepard from New Forest Farm on the other hand is convinced that the cultivation of American hazelnuts can be economic. It may only be a matter of time until the filbert blight finds it's way to Europe and wipes out the hazelnut cultivation there.
During my stay at Red Fern Farm I also learned how and when to use a special grafting method called the barn door graft. It can be done during the growing season as the bark must be slippery to do it. It is especially useful for plants that are not easy to graft like for example walnuts. Maybe this graft would also make it easier to graft chestnut onto oak, which I still find interesting to maybe make chestnuts possible on alkaline soil where they wouldn't grow normally. On their website Tom explains how to do the barn door graft: Grafting methods. The method makes it easier for the scion to grow onto the rootstock as it has a lot of attachment area but for the first years it has to be supported by binding it to the rootstock so it doesn't break off.
Some other things I learned:
- Honey locust (Gleditsia triacanthos), Kentucky Coffee Tree (Gymnocladus dioicus) and Redbud (Cercis canadensis) although members from the Fabaceae family are probably not nitrogen fixers.
- Apple variety 'Frost Bite' tastes delicious but not like apple. I am curious how it tastes, some people report strawberry or cherry or other fruit.
- Hickan (Hickory x Pekan), Buardnut (Butternut x Heartnut)
- European plum doesn't graft on American or Japanese plum. Apricots don't graft on many other Prunus spp.
- Viburnum lentago variety 'Nannyberry' is supposed to taste like dates
- Toka plum (Japanese x American) is supposed to be the tastiest plum
Jiaogulan is hardy in zone 5?! (1 of 5 plants survived an average winter here at Red Fern Farm without any further protection)