Growing Black Locust in NYS

[Carl Albers]

Black locust is one of the most rot resistant woods native to North America.  Straight black locust posts and poles are in demand by grape and hop growers, and organic farmers who wish to fence in livestock or fence out deer.  The heartwood of locust trees is the most resistant to decay so larger diameter material will be the longest lasting. 

NYS-DEC considers black locust to be invasive and there are restrictions on planting black locust in certain areas of NYS.  Before considering a black locust planting check with your local NYS-DEC forester regarding any planting restrictions in your area. 

Once established black locust is difficult to get rid of because it re-sprouts from root suckers.  Black locust has thorns which can puncture the tires on farm machinery so that should be kept in mind as well.  Because it is a pioneer species black locust is shade intolerant so it requires full sunlight to grow.  

The first task in starting a black locust plantation is proper site selection.  The locust borer (Megacyllene robiniae) is a major pest of black locust.  Avoid sites with older, borer infested (brood) trees or remove them; now older research showed a direct relationship between borer damage on young trees and proximity to existing brood trees.  Vigorously growing black locust is the best defense against borer infestations, and deep, fertile, well drained soils with good moist holding capacity promote vigor in young black locust plantations.  For those interested in growing black locust mostly for firewood soil selection is less important as you can tolerate a greater incidence of borer infestation, however, avoid clayey, poorly drained soils and excessively drained, low organic matter containing gravel, sand or soils that are shallow to bedrock for best results.  Well-drained soils in the NYS lime belt should work well for black locust.

Take a soil test, preferably a year ahead of planting.  Lime to a pH of 6.5 and fertilize with phosphorus and potassium with a goal of achieving at least medium phosphorus and potassium levels.  Plant buckwheat, sorghum-sudangrass or similar cover crop the year prior to planting to weaken any existing grass sod.

Plant only black locust from seed or root cuttings derived from existing locust stands exhibiting straight, vigorous growth.  Root cuttings are taken by following out root flares on existing trees and carefully using a fork to dig up pieces of root that are roughly 1/2-inch in diameter during the dormant season (late March to early May.)  Keep these roots moist, almost wet until you get them home and replant them.  Make a flush cut on the end of the root towards the trunk and a slanted cut on the end towards the root tip.  Replant in pots, a nursery bed, or directly by cutting the roots into roughly 6-inch pieces.  Plant with the flush end up even with the soil level in your planting medium; slant end down.  Collect some soil from near the roots you harvest or near the roots of healthy black locust trees to use as inoculum, for plantings of seeds or roots (the inoculum contains the Rhizobium bacteria that allow black locust to fix nitrogen.)  Add a teaspoonful or more of this to your planting medium; again for either seeds or roots.  For best germination seeds need to be scarified or subjected to a hot water bath.  

Layout rows on a 1 percent slope to encourage infiltration while also allow excess rainfall to move slowly offsite to reduce erosion during downpours.  Space no more widely than 20-feet by 20-feet, however, closer spacing will deter forking and side branches.  Inter-planting with a fast growing high-value, hardwood species may be helpful for promoting strong, single leaders and less side branching.  Red oak, blight resistant, timber-type chestnuts and similar species are probably good choices.  A border of fast growing hardwoods around the outside of the planting is also a good idea to deter the black locusts from growing towards the light.  

Deer and grass control are essential for vigorous growth and borer resistance.  Five foot vented tree tubes are one option for deer protection.  Fencing the entire plantation is another option and may make sense for larger plantings.

Once the plantation is established prune out forked leaders during late winter.  Control grasses.  Practice crop tree management as the canopy closes so superior specimens receive plenty of sunlight; doing so will keep the locust growing vigorously and allow it to outgrow locust borer damage to the greatest extent possible.      

[Kevin Mathers]

Hi Carl,

Thanks for the excellent info. Over the past few years we've seen increasing damage of black locust by locust leaf miner in the eastern southern tier of NY.   Do you have any thoughts on the advisability of starting a plantation in this situation?

[Carl Albers]

Hi Kevin,

Not sure what that means for the future of black locust plantations.  That would be a good question for Brett Chedzoy.  Without a crystal ball I would say don't put all your eggs in one basket.  Soil type, well-drained/moderately well drained with good moisture holding capacity (lots of organic matter) and a north or east facing slope to reduce stress will be important.  I think it will be important to lime the site, preferably before planting to a pH of 6.5...though there isn't much research on this (old research did show good results on soils with limestone parent material.)  Inter-plant with red oak, blight resistant timber type-chestnuts or similarly adapted trees...so avoid a mono culture.  Inoculate the trees with soils from healthy black locust groves so they are inoculated with nitrogen fixing rhizobia bacteria and appropriate mycorrhizal fungi.  Lay out rows on a roughly 1 percent slope to maximize infiltration, yet move excessive water away slowly to reduce the risk of erosion.  Practice crop tree management as the plantation grows so that individual trees are getting the sunlight they need to thrive.  In short, you are trying to do everything you can to increase tree vigor so that the trees can fight off pest infestations to the greatest extent possible.