Black Locust: A Tree with Many Uses

In early October this past year, a devoted group of foresters, farmers, extension educations, students, and others gathered at the USDA Plant Materials Center in Big Flats, NY to discuss a common, yet underappreciated tree that has great potential for farms across the Northeast: Black Locust (Robinia pseudoacacia).

This tree, which has often been given a bad name for it’s opportunistic rapid growth and robust thorns, is said to be native originally to the Appalachian Mountain range, though it has become naturalized throughout the United States, southern Canada, and even parts of Europe and Asia. The species is incredibly adaptive, growing in many elevations, microclimates, and soil types.

While some have named it an “invasive” tree given its rapid growth and willingness to spread by seed and root suckering, others see these characteristics as advantageous, if only populations are properly managed to harness these qualities. Make no mistake, locust is not a tree to plant and walk away from. It is best when incorporated into managed activities on the farm, of which there are a remarkable array of options and benefits, including:

• Because it fixes nitrogen from the atmosphere, the trees grow incredibly fast (3 – 4 feet in a season) and can quickly become windbreaks, shelterbelts, and shade and shelter for animals in silvopasture grazing systems.
• The nutritional value of the leaves is similar to alfalfa, making it a valuable feed for ruminant livestock. Some sources claim excessive consumption can lead to toxicity, but many farmers have found their animals naturally limit their intake. (horses excepted)
• The tree has been used to support nutrition in other crops, from grains to other trees. Research has shown increases in nitrogen in barley grain crops interplanted with locust, and black walnuts interplanted with locust as “nurse” trees were shown to rapidly increase their growth.
• The flowers are important sources of food for honeybees. In Hungary, Black Locust is the basis of commercial honey production.
• The high-density wood is the most rot resistant wood we can grow in our climate, making it an ideal material for fenceposts, hope poles, outdoor furniture, decks, and other projects that require weatherproof materials.
• It’s BTU rating is among the highest, making it an excellent firewood in both heat value and coaling ability. At our last house, we actually ruined a woodstove by burning too much locust, which gets extremely hot.

If anything, Black locust is almost too good at what is does. All theses attributes have resulted in an extraordinarily high demand; both sellers of locust poles and lumber, as well as those in the nursery trade at the meeting reported not even coming close to meeting the demand for their products. There is a lot of room in the market for more farmers to grow, harvest, and sell black locust products in many parts of the region.

The challenge? Some states prohibit importing, selling, or trading Black Locust, including Massachusetts and it is restricted in Minnesota, Michigan, and New York. This is not necessarily a complete list – check with your state regulators before deciding how to proceed. Each state has it’s own specific regulations.

In New York, a regulated plant cannot be knowingly introduced into a location where it isn’t already present. It’s hard to say if there is such a place in New York, and likely not in any location where farming traditionally occurred, since the tree has a long history of value to both Native Americans and colonizer settler farmers around the state. In any case, in New York the trees can be purchased, sold, propagated and transported legally. Nursery’s are required to attached a disclaimed to any material they sell.

Assuming you are clear to work with Black Locust, it’s important to consider the genetic stock you source trees from, especially if your goal is to grow straight poles or trees that can be milled for lumber. Locust is incredibly crooked in its “natural” form, and so seed selection, and sometimes pruning, is a critical factor for success. Ironically, the Hungarians identified the awesomeness of Black locust a long time ago (1700s), deciding to intentionally import seeds and engage in an intensive breeding program. As a result, some of the best stock today comes from Eastern Europe, and nearly 20% of the forests in Hungary are comprised of Black Locust.

Propagation of new trees is best achieved by either seed, or root cuttings. Of course, seed will express variety in the resulting genetic profile, whereas root cuttings will be clones of the parent tree. To grow from seed, the thick coat must first be broken, most often by soaking in a pot of boiling water for 12 – 24 hours. Root cuttings can be taken by finding a good flare in the tree, and digging up roots at least thumb thickness. Roots are cut into 2” sections and planted in a potting mix or prepared seed bed.

While the tree is suitable for a wide range of sites, avoid extremely heavy clay and soils with excessive water moisture (standing water). Soil prep can be minimal, as the trees can often compete and overtake other competitors quite easily. Protection from deer or other potential pests is critical during the establishment period, usually the first one to three years.

Black locust has just a few pests of concern, and a little observation and vigilance goes a long way. The health and vigor of the trees are important defenses against devastation, as research has shown that good growing conditions are more important than genetic resistance.

The most common pest is the Locust borer (Megacyllene robiniae) which most often attacks living, stressed trees, causing extensive damage to the quality of the wood. Identifying and removing infected trees can go a long way. It’s critical get to know the lifecycle of the pest. The other is main pest is the leaf miner (Odontota dorsalis), which attacks the tree in spring, turning the leaves brown by mid-summer or early fall. Overall tree growth can be impacted, but usually not seriously.

One of the most exciting conversations at the meeting was around the good economics for Black Locust, which can be summarized as demand far outstripping the supply. A recent blossoming of interest in natural and sustainable materials for garden and fence posts, coupled with a boom in the hop production industry in the Northeast mean that black locust polewood (which requires only harvesting and cutting to length) can alone be a valuable product from the farm woodlot. Larger, straight trees can also be milled and either sold as lumber or made into a wide range of products include outdoor furniture and offered at a premium price. Prices for these products range from $1 – $3 per linear foot for whole posts, and from $1.50 – $3.50/board foot for milled lumber, which is far above the prices for most conventional hardwood lumber.

Personally, at our farm, Black locust has found a nice in our pastures, where it quickly establishes itself and is able to be integrated with our sheep grazing paddocks in under 5 years. The sheep initially prune the lower limbs for feed, and we prune thicker branches to use for tree stakes, to plant more trees! We plant very close together (3 – 4 feet apart) so that over time, we can leave some trees as the overstory, while coppicing (cutting to the ground) and pollarding (cutting above browse height) the less straight ones to provide longer-term fodder reserves for the sheep. Eventually we can harvest some posts and poles, as well.

With all its functions and uses in the farm landscape, it’s a wonder more people aren’t planting these trees, and managing ones they already have. The key take away is; if you plant it, manage it. This wonderful tree has many benefits to harvest, but left along could become a problem plant on the farm.

Sources for Trees and Seeds:

Twisted Tree Farm, NY: http://twisted-tree.net/

Edible Acres, NY: http://edibleacres.org/

Sheffield’s Seeds, NY: https://sheffields.com

Cold Stream Farm, MI: https://www.coldstreamfarm.net

More information and slides from the workshop can be found at: http://silvopasture.ning.com/forum/topics/growing-black-locust-as-a-timber-cash-crop-in-the-northeast

This article is available for download at Wellspring Forest Farm & School’s website: https://www.wellspringforestfarm.com/