How to Grow Black Locust Trees from Seed
Black Locust trees can be a great addition to your landscape. Learning how to grow them from seed is easy, rewarding, and cost-effective!
Whether you recognize it or not, chances are you’ve seen a Black Locust tree before. The Black Locust is native to the Appalachian Mountain range, but it has been planted widely and is considered naturalized throughout the United States, as well as parts of Canada, Europe and Asia.
Because of its hardiness, it’s sometimes considered an invasive tree. However, there are several uses and benefits that make it a desirable tree to many.
I’ve recently started Black Locust from seed, so I thought I would share why you might consider planting Black Locust trees and how to start them from seed.
How to Identify a Black Locust Tree
First, let’s identify the Black Locust tree, or Robinia pseudoacacia. They grow in USDA zones 4-9 and are well-adapted to hot, dry regions. The leaves are divided in a feather-like manner with many rounded leaflets. Blooming in midspring to early summer, their white, sweet-pea shaped flowers are held in dense, pendant clusters.
Following flowering, the branches will have bean-like, leathery seed pods about 4 inches long. The Black Locust grows 40-75 feet tall and 30-60 feet wide, with an open branching habit. The bark is dark grayish-brown and deeply furrowed. The branches have rather large thorns.
Why Plant Black Locust Trees
There are several reasons why one might plant a Black Locust tree. However, these are my top three reasons why Black Locust caught my attention initially.
Fast-growing – Black Locusts grow, on average, 2-4 feet per year. Some have been known to reach heights of over 40 feet in 10 years.
Easy to grow – Black Locust can tolerate a wide range of conditions, including poor soil and little to no water.
Attractive shade tree – Although the leaves are on the smaller side compared to traditional shade trees, Black Locust trees do provide some nice filtered shade. Planted in groupings, they can provide dense shade.
Looking for more shade trees? Head on over to our post on The Best Shade Trees for Zone 8
Can be grown from seed – Black Locust seed pods are usually abundant and easy to collect. The seeds can be germinated pretty easily with just a couple simple steps, making it a great choice for beginners.
Benefits & Uses of Black Locust Trees
Fix Nitrogen – Perhaps the most significant benefit of Black Locust trees are their ability to fix nitrogen from the atmosphere. The tree manufactures its own fertilizer by way of nitrogen-fixing root nodule bacteria, which contributes to its fast growth and ability to grow in poor soil.
Their nitrogen-fixing abilities can improve the soil, and in turn, other plants’ growth rates as well. They have been interplanted with other species as “nurse trees” to rapidly enhance growth.
Food source for honeybees – The flowers that bloom midspring to early summer can be an important food source for local honeybee populations.
Makes good firewood – Black Locust can make good firewood as it burns hot and produces relatively little smoke. It’s similar to Oak in terms of energy, and produces almost 28 million BTUs per cord. However, since it is very high density, hard wood, it can be difficult to split by hand.
Relatively rot resistant – the wood of Black Locust is relatively rot resistant, making it a good choice for outdoor furniture, fence posts, and other outdoor projects requiring weatherproof materials.
Growth Rate and Care of Black Locust
As mentioned above, Black Locust trees grow rapidly at 2-4 feet per year, which can be good and bad. It’s great for those who want a fast growing tree for windbreaks, privacy screens, and shade. However, they are quite opportunistic – they can take over an area by way of root suckering and stump sprouting if not kept in check.
Although Black Locusts are easy to care for, don’t expect to just plant them and walk away. They will require some maintenance to make sure they don’t become invasive – particularly in the prairies of the Midwest.
As far as care goes, these trees are pretty easy keepers. They do prefer full sun and well-draining soil, but they can tolerate a variety of conditions. Below is a quick reference guide of basic care tips for Black Locust trees.
How to Care for Black Locust Trees
- Climate: Black Locusts can tolerate a wide range in temperatures. USDA Zones 4-9.
- Soil: While they prefer well-draining soil, they can grow in almost any soil type except for extremely wet soils that never dry out. Avoid creek banks, wetlands and marshes.
- Light: Black Locusts thrive in full sun, although they will tolerate light shade as well.
- Water: Once established, Black Locust trees can tolerate drought. However, they will require regular watering when they’re young and freshly planted.
- Fertilizer: Since Black Locusts are nitrogen-fixers, they almost never require fertilization.
- Pruning: While pruning is not required, you may prune Black Locusts to shape the canopy.
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How to Start Black Locust Trees from Seed
Starting Black Locust Trees from seed is actually pretty simple. Although it is best to collect seeds in the fall and sow them in the spring, I collected the seed pods and started the seeds very late this spring and I’ve been pleasantly surprised with how well they are doing!
Here’s a basic overview of the process:
- Collect the seed pods
- Prepare the seeds
- Sow the seeds
- Keep the soil evenly moist and in a dark location while the seeds germinate
- Once seedlings emerge, move to a cool but sunny location and keep evenly moist until ready to transplant
What You Will Need
Seed starting trays or small pots
Seed starting mix (regular potting soil should work just fine as well)
Boiling water
Heat-proof bowl or cup
Seed-Starting Process
First, collect seeds pods from established trees. Each seed pod contains several seeds, so you probably won’t need more than a handful of seed pods.
Next, remove the seeds from the seed pods and place in the heat-proof bowl or cup. Cover the seeds with boiling water and let them soak for 24 hours.
When you’re ready to sow your seeds, prepare seed trays with soil. Plant the seeds about 1/4 inch deep and cover with soil. I would only advise to sow only one, maybe two, seeds per cell. I planted 2-3 seeds per cell as I didn’t expect the germination rate to be that great, and I have some cells where all the seeds germinated!
Place the tray in a cool, dark location and keep the soil evenly moist while the seeds germinate. Seedlings should emerge in 7-14 days.
Continue to keep the soil evenly moist as the seedlings grow, until you are ready to transplant. Once transplanted, the young seedlings will need protection from deer and other potential pests until established (usually the first 1-3 years).
I hope this post was helpful, and maybe even inspired you to go plant some Black Locust seeds! Let me know how it goes with a comment below, and don’t forget to share!
