Plant Profile- Chestnut

One major influence on my approach to growing has been Mark Shepard. This pioneer of agroforestry moved to a part of the USA that everyone thought was too cold for chestnuts and proceeded to develop his own highly successful and productive forest system. His strategy was pretty simple- plant as much diversity as he could get his hands on and then let the plants themselves decide if they wanted to grow and produce or not. Every time a tree died Mark said thank you as it was weeding itself out of the gene pool. He now has his own locally adapted strain of chestnuts (among many other species) that produces well far outside the previously accepted range. When I reached out to Mark at the start of developing my farm his excellent advice was to start with the most locally adapted species, including our criminally underappreciated bunya nuts. I decided to at least dabble with chestnuts as well to see if I could develop them in the other direction to adapt to a hot and humid climate.

Chestnuts have some considerable advantages over other trees. The nuts they produce are rich in starch (unlike most other oily nuts), making them a useful staple crop. Ancient societies frequently relied on chestnuts for a substantial part of their diet, especially during years when their grain crops failed. The nuts form in spiny burrs that are quite effective at deterring parrots. The trees are also relatively fast growing and can mature quite quickly as well. Experimental breeding work in the early 20^th century by the incomparable self-taught plant breeder, Luther Burbank, revealed it was possible for trees to start flowering six months from seed. This sounds incredibly exciting, but following up on this work it turns out those ultra-precocious forms put so much energy into nut production they struggle to grow into a reasonable sized tree after many years. Like most things in biology there are trade-offs between different functions so there is no free lunch. Chestnuts can produce 500-1000 kg of nuts per acre, comparable to industrial corn at 3500 kg per acre, but chestnuts do it without the annual ploughing and erosion and can be intercropped with other plants.

My initial experiments with chestnuts started with grafted and seedling trees bought from an interstate specialty tree nursery. This nursery produces excellent quality trees and stock varieties that are otherwise impossible to find, so I am very grateful that they are in business and charging the prices necessary to be sustainable as a business. The trees were planted in a section of orchard that I noticed had especially friable soil since I had read that chestnuts dislike waterlogged soil. They were planted into the weedy former cow paddock, given tree guards and watered a half dozen times with dripper bottles (1.25 L PET drink bottles with two holes drilled in the lid, placed upside down in the tree guards). While the trees seemed to grow reasonably well to begin over time they petered out one by one, often years after planting. Whether the cause was too much water or drought I don’t really care since I wasn’t going to break my back trying to mitigate either. One graft has persisted to this date and luckily it has some precocious and productive traits that are noteworthy.

At the same time I hedged by bets and tried a few different approaches. A bundle of seedlings arrived from an ebay seller in Townsville, with no information on their origins. These sad little plants arrived bare rooted, wrapped in damp paper and with barely any roots. I didn’t hold much hope of them growing but planted them out into tree guards, watered once and forgot them. Around the same time I also tried sowing chestnuts from the shops, both in pots and direct in the ground. Germinating chestnuts in pots is tricky since the large seed seem to need abundant oxygen to sprout without rotting. Barely burying them under a layer of coarse mulch or a sheet of hessian seems to suit them. Those in the ground were also barely covered. Those in pots germinated reasonably well but only gave less than 50% transplant success, another plant that resents root disturbance. Those direct sowed germinated at a bit over 50 % and I was surprised the rats didn’t take them all. Plants derived from all these different methods are now well established about five years later, with the tallest ones reaching 4-5 m in height. This is despite them not being watered, weeded, fertilised, sprayed or pruned and being buried in grasses and weeds most of their lives.

The seed grown trees are now reaching maturity, producing sickly smelling catkins in spring as the leaves burst out of winter dormancy. With a dozen or so mature trees flowering their wind pollinated flowers are more likely to cross with a neighbour. Like a lot of trees chestnuts benefit from growing in colonies with diverse genetics to ensure good pollination. In previous years seed has mostly set on my single grafted clone, presumably from pollen off some of the seedlings since its seed set improved dramatically as they started to flower alongside it. These seed that are produced in autumn are germinated each year and planted out the following spring to fill in gaps in the chestnut grove. Every year, especially during our hot and wet summers, a tree or two drops dead. As long as enough remain to produce seed and start new generations I am not too worried. If they all die then I will probably end my chestnut experiment, satisfied I gave it a decent try. If not they will continue to settle into the farm and spread to any space that suits them.

My tallest seed grown tree at about 5 m tall, astonishingly rapid growth for five years from seed.

Male catkins on a seed grown tree, 2 m tall after 5 years.

One of this years seedlings, freshly transplanted

Female catkins on a seed grown tree